<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Surface Friction & Air Resistance</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      color: #1e2945;
      background: transparent;
      padding: 10px;
      display: flex;
      flex-direction: column;
      gap: 12px;
      min-height: 100%;
    }
    .grid {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 12px;
      width: 100%;
    }
    @media (max-width: 480px) {
      .grid {
        grid-template-columns: 1fr;
      }
    }
    .comparison-card {
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 12px;
      padding: 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      box-shadow: 0 1px 3px rgba(0,0,0,0.06);
    }
    .card-title {
      font-size: 15px;
      font-weight: 700;
      color: #1e2945;
      margin-bottom: 8px;
      text-align: center;
    }
    .scene-container {
      width: 100%;
      height: 180px;
      position: relative;
      display: flex;
      align-items: center;
      justify-content: center;
      background: #f8fafc;
      border-radius: 8px;
      overflow: hidden;
      border: 1px solid #f1f5f9;
    }
    .banner {
      background: #eff6ff;
      border: 1.5px solid #bfdbfe;
      border-radius: 10px;
      padding: 11px 14px;
      text-align: center;
      font-size: 13.5px;
      font-weight: 700;
      color: #1e2945;
      line-height: 1.35;
    }
    svg {
      width: 100%;
      height: 100%;
      display: block;
    }
    .arrow-text {
      font-size: 11px;
      font-weight: 700;
      font-family: inherit;
    }
    .ground-text {
      font-size: 10px;
      font-weight: 600;
      fill: #475569;
    }
  </style>
</head>
<body>

  <div class="grid">
    
    <div class="comparison-card">
      <div class="card-title">Surface Friction</div>
      <div class="scene-container">
        <svg viewBox="0 0 210 170" xmlns="http://www.w3.org/2000/svg">
          
          <rect x="0" y="112" width="210" height="58" fill="#e2e8f0" />
          <line x1="0" y1="112" x2="210" y2="112" stroke="#94a3b8" stroke-width="2" stroke-dasharray="5 3" />
          <text x="105" y="162" text-anchor="middle" class="ground-text">Concrete Ground</text>

          
          <g>
            <rect x="62" y="6" width="76" height="17" rx="4" fill="#dbeafe" stroke="#bfdbfe" stroke-width="1" />
            <text x="100" y="18" text-anchor="middle" fill="#2563eb" class="arrow-text">Motion →</text>
            <path d="M 60 29 L 140 29" stroke="#2563eb" stroke-width="3" stroke-linecap="round" />
            <polygon points="148,29 138,24 138,34" fill="#2563eb" />
          </g>

          
          <g>
            
            <path d="M 46 102 C 45 88 52 62 76 56 C 88 53 96 66 105 76 L 138 78 C 152 79 164 88 162 102 Z" fill="#3b82f6" stroke="#1d4ed8" stroke-width="1.5" />
            
            <ellipse cx="80" cy="59" rx="9" ry="5" fill="#1e40af" />
            
            <path d="M 88 64 L 98 76" stroke="#ffffff" stroke-width="2.5" stroke-linecap="round" />
            <path d="M 96 67 L 106 78" stroke="#ffffff" stroke-width="2.5" stroke-linecap="round" />
            <path d="M 60 100 Q 95 86 145 92" stroke="#60a5fa" stroke-width="3" fill="none" stroke-linecap="round" />
            
            <path d="M 44 102 L 163 102 C 166 102 167 106 165 111 C 164 112 160 112 155 112 L 44 112 C 40 112 40 102 44 102 Z" fill="#ffffff" stroke="#94a3b8" stroke-width="1.2" />
            
            <line x1="60" y1="108" x2="60" y2="112" stroke="#94a3b8" stroke-width="1.5" />
            <line x1="80" y1="108" x2="80" y2="112" stroke="#94a3b8" stroke-width="1.5" />
            <line x1="100" y1="108" x2="100" y2="112" stroke="#94a3b8" stroke-width="1.5" />
            <line x1="120" y1="108" x2="120" y2="112" stroke="#94a3b8" stroke-width="1.5" />
            <line x1="140" y1="108" x2="140" y2="112" stroke="#94a3b8" stroke-width="1.5" />
          </g>

          
          <g>
            
            <path d="M 152 121 L 58 121" stroke="#dc2626" stroke-width="3" stroke-linecap="round" />
            <polygon points="48,121 60,115 60,127" fill="#dc2626" />
            
            <rect x="66" y="131" width="78" height="17" rx="4" fill="#fee2e2" stroke="#fca5a5" stroke-width="1" />
            <text x="105" y="143" text-anchor="middle" fill="#dc2626" class="arrow-text">Friction</text>
          </g>
        </svg>
      </div>
    </div>

    
    <div class="comparison-card">
      <div class="card-title">Air Resistance</div>
      <div class="scene-container">
        <svg viewBox="0 0 210 170" xmlns="http://www.w3.org/2000/svg">
          
          <g fill="#93c5fd">
            <circle cx="68" cy="28" r="2.5" />
            <circle cx="175" cy="30" r="3" />
            <circle cx="185" cy="72" r="2.5" />
            <circle cx="70" cy="138" r="2.5" />
            <circle cx="178" cy="125" r="3" />
            <circle cx="188" cy="148" r="2.5" />
          </g>

          
          <g fill="#3b82f6">
            <circle cx="108" cy="120" r="3" />
            <circle cx="122" cy="124" r="3.5" />
            <circle cx="138" cy="120" r="3" />
            <circle cx="95" cy="108" r="2.5" />
            <circle cx="150" cy="108" r="2.5" />
          </g>

          
          <path d="M 112 128 Q 94 112 88 92" stroke="#93c5fd" stroke-width="1.8" fill="none" stroke-linecap="round" />
          <path d="M 134 128 Q 152 112 158 92" stroke="#93c5fd" stroke-width="1.8" fill="none" stroke-linecap="round" />

          
          <g>
            <circle cx="122" cy="74" r="24" fill="#f97316" stroke="#ea580c" stroke-width="2" />
            
            <ellipse cx="114" cy="65" rx="7" ry="3.5" fill="#fdba74" transform="rotate(-30 114 65)" />
          </g>

          
          <g>
            <rect x="4" y="28" width="64" height="17" rx="4" fill="#dbeafe" stroke="#bfdbfe" stroke-width="1" />
            <text x="36" y="40" text-anchor="middle" fill="#2563eb" class="arrow-text">Motion ↓</text>
            <path d="M 36 51 L 36 106" stroke="#2563eb" stroke-width="3" stroke-linecap="round" />
            <polygon points="36,115 31,103 41,103" fill="#2563eb" />
          </g>

          
          <g>
            <rect x="70" y="6" width="104" height="17" rx="4" fill="#fee2e2" stroke="#fca5a5" stroke-width="1" />
            <text x="122" y="18" text-anchor="middle" fill="#dc2626" class="arrow-text">Air Resistance ↑</text>
            <path d="M 122 108 L 122 36" stroke="#dc2626" stroke-width="3.5" stroke-linecap="round" />
            <polygon points="122,27 116,39 128,39" fill="#dc2626" />
          </g>
        </svg>
      </div>
    </div>
  </div>

  
  <div class="banner">
    Both are friction forces that push against motion!
  </div>

</body>
</html>

Air Resistance: Pushing Against Moving Objects

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="1:1">
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    }
    body {
      width: 100%;
      background: #ffffff;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      padding: 12px 8px;
      user-select: none;
    }

    /* Tab Switcher */
    .tabs {
      display: flex;
      gap: 8px;
      width: 100%;
      max-width: 350px;
      margin-bottom: 12px;
    }
    .tab-btn {
      flex: 1;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      padding: 10px 8px;
      font-size: 14px;
      font-weight: 700;
      border-radius: 10px;
      border: 2px solid #e6e6e6;
      background: #f8fafc;
      color: #64748b;
      cursor: pointer;
      transition: all 0.25s ease;
    }
    .tab-btn.active {
      background: #eff6ff;
      border-color: #22b7ff;
      color: #0369a1;
      box-shadow: 0 2px 8px rgba(34, 183, 255, 0.15);
    }

    /* Stage Area */
    .stage {
      position: relative;
      width: 100%;
      max-width: 350px;
      height: 290px;
      background: #f8fafc;
      border-radius: 16px;
      border: 1px solid #e6e6e6;
      overflow: hidden;
    }

    .scene {
      position: absolute;
      inset: 0;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      opacity: 0;
      pointer-events: none;
      transition: opacity 0.3s ease, transform 0.3s ease;
      transform: scale(0.96);
    }
    .scene.active {
      opacity: 1;
      pointer-events: auto;
      transform: scale(1);
    }

    /* Force Arrow Badges */
    .arrow-badge {
      display: inline-flex;
      align-items: center;
      gap: 6px;
      padding: 6px 12px;
      border-radius: 20px;
      font-size: 14px;
      font-weight: 800;
      letter-spacing: 0.2px;
      box-shadow: 0 2px 6px rgba(0, 0, 0, 0.06);
    }
    .badge-resist {
      background: #fee2e2;
      color: #dc2626;
      border: 1.5px solid #fca5a5;
    }
    .badge-move {
      background: #dcfce7;
      color: #15803d;
      border: 1.5px solid #86efac;
    }

    /* Scene Layouts */
    .skydiver-layout {
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      height: 100%;
      padding: 18px 0;
    }
    .cyclist-layout {
      display: flex;
      align-items: center;
      justify-content: space-between;
      width: 100%;
      padding: 0 12px;
    }

    .actor-box {
      position: relative;
      font-size: 62px;
      line-height: 1;
      display: flex;
      align-items: center;
      justify-content: center;
    }

    /* Vector Arrows */
    .arrow-svg {
      overflow: visible;
    }
  </style>
</head>
<body>

  
  <div class="tabs" role="tablist">
    <button class="tab-btn active" id="tab-sky" onclick="showScene('sky')" role="tab" aria-selected="true">
      <span>🪂</span> Falling Skydiver
    </button>
    <button class="tab-btn" id="tab-cyc" onclick="showScene('cyc')" role="tab" aria-selected="false">
      <span>🚴</span> Speeding Cyclist
    </button>
  </div>

  
  <div class="stage">
    
    
    <div class="scene active" id="scene-sky">
      <div class="skydiver-layout">
        
        
        <div style="display: flex; flex-direction: column; align-items: center; gap: 4px;">
          <div class="arrow-badge badge-resist">
            <span>▲</span> Air Resistance
          </div>
          <svg class="arrow-svg" width="24" height="28" viewBox="0 0 24 28">
            <path d="M12 28 L12 8 M5 12 L12 3 L19 12" fill="none" stroke="#dc2626" stroke-width="4.5" stroke-linecap="round" stroke-linejoin="round"/>
          </svg>
        </div>

        
        <div class="actor-box">
          🪂
        </div>

        
        <div style="display: flex; flex-direction: column; align-items: center; gap: 4px;">
          <svg class="arrow-svg" width="24" height="28" viewBox="0 0 24 28">
            <path d="M12 0 L12 20 M5 16 L12 25 L19 16" fill="none" stroke="#16a34a" stroke-width="4.5" stroke-linecap="round" stroke-linejoin="round"/>
          </svg>
          <div class="arrow-badge badge-move">
            <span>▼</span> Movement
          </div>
        </div>

      </div>
    </div>

    
    <div class="scene" id="scene-cyc">
      <div class="cyclist-layout">
        
        
        <div style="display: flex; flex-direction: column; align-items: center; gap: 6px; min-width: 105px;">
          <div class="arrow-badge badge-resist" style="padding: 6px 8px; font-size: 13px;">
            <span>◀</span> Air Resistance
          </div>
          <svg class="arrow-svg" width="46" height="20" viewBox="0 0 46 20">
            <path d="M46 10 L10 10 M16 4 L4 10 L16 16" fill="none" stroke="#dc2626" stroke-width="4.5" stroke-linecap="round" stroke-linejoin="round"/>
          </svg>
        </div>

        
        <div class="actor-box" style="margin: 0 4px;">
          🚴
        </div>

        
        <div style="display: flex; flex-direction: column; align-items: center; gap: 6px; min-width: 105px;">
          <div class="arrow-badge badge-move" style="padding: 6px 10px; font-size: 13px;">
            Movement <span>▶</span>
          </div>
          <svg class="arrow-svg" width="46" height="20" viewBox="0 0 46 20">
            <path d="M0 10 L36 10 M30 4 L42 10 L30 16" fill="none" stroke="#16a34a" stroke-width="4.5" stroke-linecap="round" stroke-linejoin="round"/>
          </svg>
        </div>

      </div>
    </div>

  </div>

  <script>
    function showScene(type) {
      const isSky = type === 'sky';
      document.getElementById('scene-sky').classList.toggle('active', isSky);
      document.getElementById('scene-cyc').classList.toggle('active', !isSky);
      
      const tabSky = document.getElementById('tab-sky');
      const tabCyc = document.getElementById('tab-cyc');
      
      tabSky.classList.toggle('active', isSky);
      tabCyc.classList.toggle('active', !isSky);
      
      tabSky.setAttribute('aria-selected', isSky);
      tabCyc.setAttribute('aria-selected', !isSky);
    }
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Air Resistance on a Runner</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      user-select: none;
      -webkit-user-select: none;
    }

    body {
      width: 100%;
      background: transparent;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      padding: 6px 4px;
    }

    .canvas-container {
      position: relative;
      width: 100%;
      max-width: 460px;
      aspect-ratio: 480 / 330;
      background: #f8f9fa;
      border: 1px solid #e6e6e6;
      border-radius: 12px;
      overflow: hidden;
    }

    canvas {
      display: block;
      width: 100%;
      height: 100%;
    }

    .ui-overlay {
      position: absolute;
      top: 8px;
      right: 8px;
      display: flex;
      justify-content: flex-end;
      align-items: center;
      pointer-events: none;
      z-index: 10;
    }

    .legend {
      display: flex;
      flex-direction: column;
      gap: 5px;
      background: rgba(255, 255, 255, 0.95);
      border: 1px solid #e2e8f0;
      padding: 6px 10px;
      border-radius: 8px;
      font-size: 11px;
      font-weight: 600;
      box-shadow: 0 1px 4px rgba(0, 0, 0, 0.05);
    }

    .legend-item {
      display: flex;
      align-items: center;
      gap: 6px;
      white-space: nowrap;
    }

    .dot-air {
      width: 8px;
      height: 8px;
      background: #2563eb;
      border-radius: 50%;
      display: inline-block;
    }

    .arrow-force {
      color: #dc2626;
      font-weight: 800;
      font-size: 13px;
      line-height: 1;
    }

    .controls {
      display: flex;
      gap: 8px;
      margin-top: 8px;
      margin-bottom: 2px;
      width: 100%;
      max-width: 460px;
      justify-content: center;
    }

    .btn {
      flex: 1;
      max-width: 140px;
      padding: 8px 10px;
      background: #ffffff;
      border: 1px solid #d1d5db;
      border-radius: 10px;
      font-size: 12px;
      font-weight: 600;
      color: #1e2945;
      cursor: pointer;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 5px;
      transition: background-color 0.35s ease, border-color 0.35s ease, color 0.35s ease;
    }

    .btn:active {
      background: #f1f5f9;
    }

    .btn.active {
      background: #1e2945;
      color: #ffffff;
      border-color: #1e2945;
    }

    @media (min-width: 400px) {
      .btn {
        font-size: 13px;
        padding: 8px 14px;
      }
      .legend {
        font-size: 12px;
        padding: 6px 12px;
      }
    }
  </style>
</head>
<body>

  <div class="canvas-container">
    <canvas id="simCanvas" width="480" height="330"></canvas>
    <div class="ui-overlay">
      <div class="legend">
        <div class="legend-item">
          <span class="dot-air"></span>
          <span>Air particles</span>
        </div>
        <div class="legend-item">
          <span class="arrow-force">←</span>
          <span>Push-back force</span>
        </div>
      </div>
    </div>
  </div>

  <div class="controls">
    <button id="btnNormal" class="btn active">▶ Normal</button>
    <button id="btnSlow" class="btn">⏳ Slow Motion</button>
    <button id="btnPause" class="btn">⏸ Pause</button>
  </div>

  <script>
    const canvas = document.getElementById('simCanvas');
    const ctx = canvas.getContext('2d');

    let speedMode = 'normal';
    let lastTime = performance.now();
    let animTime = 0;

    const btnNormal = document.getElementById('btnNormal');
    const btnSlow = document.getElementById('btnSlow');
    const btnPause = document.getElementById('btnPause');

    function setSpeed(mode) {
      speedMode = mode;
      btnNormal.classList.toggle('active', mode === 'normal');
      btnSlow.classList.toggle('active', mode === 'slow');
      btnPause.classList.toggle('active', mode === 'paused');
    }

    btnNormal.addEventListener('click', () => setSpeed('normal'));
    btnSlow.addEventListener('click', () => setSpeed('slow'));
    btnPause.addEventListener('click', () => setSpeed('paused'));

    const runnerX = 135;
    const groundY = 260;

    const PARTICLE_COUNT = 50;
    const particles = [];
    const impactArrows = [];

    function initParticles() {
      for (let i = 0; i < PARTICLE_COUNT; i++) {
        particles.push({
          x: 100 + Math.random() * 370,
          y: 40 + Math.random() * 215,
          vx: -(1.4 + Math.random() * 0.8),
          vy: (Math.random() - 0.5) * 0.2,
          radius: 3.5,
          collided: false,
          colorT: 0
        });
      }
    }
    initParticles();

    function resetParticle(p) {
      p.x = 480 + Math.random() * 30;
      p.y = 45 + Math.random() * 210;
      p.vx = -(1.4 + Math.random() * 0.8);
      p.vy = (Math.random() - 0.5) * 0.2;
      p.collided = false;
      p.colorT = 0;
    }

    function checkCollision(p) {
      if (p.collided) return;

      const headCenterX = runnerX + 22;
      const headCenterY = 96;
      const headDist = Math.hypot(p.x - headCenterX, p.y - headCenterY);

      let hit = false;
      let impactOriginX = p.x;
      let impactOriginY = p.y;

      // Head collision
      if (headDist < 16 && p.x >= headCenterX) {
        hit = true;
        impactOriginX = headCenterX + 12;
        impactOriginY = p.y;
        p.vx = Math.abs(p.vx) * 0.5 + 0.4;
        p.vy = (p.y - headCenterY) * 0.12 + (Math.random() - 0.5) * 0.5;
      }
      // Chest / Upper Torso collision
      else if (p.x >= runnerX + 16 && p.x <= runnerX + 34 && p.y >= 115 && p.y <= 170) {
        hit = true;
        impactOriginX = runnerX + 26;
        impactOriginY = p.y;
        p.vx = Math.abs(p.vx) * 0.6 + 0.5;
        p.vy = (p.y - 142) * 0.04 + (Math.random() - 0.5) * 0.6;
      }
      // Lower Torso / Thigh collision
      else if (p.x >= runnerX + 8 && p.x <= runnerX + 30 && p.y > 170 && p.y <= 225) {
        hit = true;
        impactOriginX = runnerX + 22;
        impactOriginY = p.y;
        p.vx = Math.abs(p.vx) * 0.55 + 0.4;
        p.vy = 0.35 + (Math.random() - 0.5) * 0.4;
      }

      if (hit) {
        p.collided = true;
        p.colorT = 1.0;

        impactArrows.push({
          x: impactOriginX,
          y: impactOriginY,
          maxLife: 0.45,
          life: 0.45,
          len: 16
        });
      }
    }

    // Draws a left-pointing pushback arrow
    function drawPointingLeftArrow(startX, startY, length, color, lineWidth = 2) {
      const endX = startX - length;
      const headSize = 5;

      ctx.save();
      ctx.strokeStyle = color;
      ctx.fillStyle = color;
      ctx.lineWidth = lineWidth;
      ctx.lineCap = 'round';
      ctx.lineJoin = 'round';

      // Stem
      ctx.beginPath();
      ctx.moveTo(startX, startY);
      ctx.lineTo(endX, startY);
      ctx.stroke();

      // Arrowhead pointing LEFT
      ctx.beginPath();
      ctx.moveTo(endX, startY);
      ctx.lineTo(endX + headSize, startY - headSize * 0.7);
      ctx.lineTo(endX + headSize, startY + headSize * 0.7);
      ctx.closePath();
      ctx.fill();
      ctx.restore();
    }

    function drawRunner(t) {
      ctx.save();

      // Ground line
      ctx.strokeStyle = '#e2e8f0';
      ctx.lineWidth = 3;
      ctx.beginPath();
      ctx.moveTo(0, groundY);
      ctx.lineTo(480, groundY);
      ctx.stroke();

      // Running cycle phase (smooth stride)
      const legPhase = Math.sin(t * 3.2);
      const armPhase = Math.cos(t * 3.2);

      // Back Arm
      ctx.strokeStyle = '#94a3b8';
      ctx.lineWidth = 4.5;
      ctx.lineCap = 'round';
      ctx.beginPath();
      ctx.moveTo(runnerX + 5, 132);
      ctx.lineTo(runnerX - 14 - armPhase * 10, 155);
      ctx.stroke();

      // Back Leg
      ctx.strokeStyle = '#64748b';
      ctx.lineWidth = 5.5;
      ctx.lineCap = 'round';
      ctx.beginPath();
      ctx.moveTo(runnerX, 180);
      ctx.lineTo(runnerX - 22 - legPhase * 14, 220);
      ctx.lineTo(runnerX - 30 - legPhase * 16, 258);
      ctx.stroke();

      // Torso
      ctx.strokeStyle = '#1e2945';
      ctx.lineWidth = 13;
      ctx.lineCap = 'round';
      ctx.beginPath();
      ctx.moveTo(runnerX - 2, 180);
      ctx.lineTo(runnerX + 16, 122);
      ctx.stroke();

      // Head
      ctx.fillStyle = '#1e2945';
      ctx.beginPath();
      ctx.arc(runnerX + 22, 96, 13.5, 0, Math.PI * 2);
      ctx.fill();

      // Front Leg
      ctx.strokeStyle = '#1e2945';
      ctx.lineWidth = 6.5;
      ctx.lineCap = 'round';
      ctx.beginPath();
      ctx.moveTo(runnerX + 4, 180);
      ctx.lineTo(runnerX + 18 + legPhase * 13, 220);
      ctx.lineTo(runnerX + 14 + legPhase * 16, 258);
      ctx.stroke();

      // Front Arm
      ctx.strokeStyle = '#1e2945';
      ctx.lineWidth = 5.5;
      ctx.lineCap = 'round';
      ctx.beginPath();
      ctx.moveTo(runnerX + 14, 128);
      ctx.lineTo(runnerX + 25 + armPhase * 10, 150);
      ctx.lineTo(runnerX + 32 + armPhase * 8, 142);
      ctx.stroke();

      // Motion Pill Badge (above runner)
      const mBadgeX = runnerX - 55;
      const mBadgeY = 38;
      ctx.save();
      ctx.fillStyle = 'rgba(238, 246, 255, 0.95)';
      ctx.strokeStyle = '#0284c7';
      ctx.lineWidth = 1.5;
      ctx.beginPath();
      ctx.roundRect(mBadgeX, mBadgeY, 80, 22, 6);
      ctx.fill();
      ctx.stroke();

      ctx.fillStyle = '#0369a1';
      ctx.font = 'bold 11px system-ui, sans-serif';
      ctx.textAlign = 'center';
      ctx.textBaseline = 'middle';
      ctx.fillText('Motion ➔', mBadgeX + 40, mBadgeY + 11);
      ctx.restore();

      // Air Resistance Badge and Resultant Force Arrow
      // Badge is placed ABOVE the arrow so arrow never passes through text
      const rBadgeX = runnerX + 48;
      const rBadgeY = 112;
      const badgeWidth = 100;
      const badgeHeight = 22;

      ctx.save();
      ctx.fillStyle = 'rgba(254, 242, 242, 0.95)';
      ctx.strokeStyle = '#ef4444';
      ctx.lineWidth = 1.5;
      ctx.beginPath();
      ctx.roundRect(rBadgeX, rBadgeY, badgeWidth, badgeHeight, 6);
      ctx.fill();
      ctx.stroke();

      ctx.fillStyle = '#b91c1c';
      ctx.font = 'bold 11px system-ui, sans-serif';
      ctx.textAlign = 'center';
      ctx.textBaseline = 'middle';
      ctx.fillText('Air Resistance', rBadgeX + badgeWidth / 2, rBadgeY + badgeHeight / 2);
      ctx.restore();

      // Large Main Backward Force Arrow below the badge (originating at chest boundary)
      const arrowStartX = rBadgeX + badgeWidth - 8;
      const arrowStartY = rBadgeY + badgeHeight + 12;
      const arrowLen = badgeWidth + 8;
      drawPointingLeftArrow(arrowStartX, arrowStartY, arrowLen, '#dc2626', 3);

      ctx.restore();
    }

    function animate(currentTime) {
      const dt = Math.min((currentTime - lastTime) / 1000, 0.05);
      lastTime = currentTime;

      let speedMultiplier = 1.0;
      if (speedMode === 'slow') speedMultiplier = 0.3;
      else if (speedMode === 'paused') speedMultiplier = 0;

      animTime += dt * speedMultiplier;

      // Update particles
      for (const p of particles) {
        if (speedMultiplier > 0) {
          p.x += p.vx * speedMultiplier;
          p.y += p.vy * speedMultiplier;

          if (p.collided) {
            p.colorT = Math.max(0, p.colorT - dt * 2.0);
          }

          checkCollision(p);

          if (p.x < -10 || p.x > 500 || p.y < 20 || p.y > 300) {
            resetParticle(p);
          }
        }
      }

      // Update impact red force arrows
      for (let i = impactArrows.length - 1; i >= 0; i--) {
        const arrow = impactArrows[i];
        if (speedMultiplier > 0) {
          arrow.life -= dt * (speedMode === 'slow' ? 0.8 : 2.2);
          arrow.x -= 0.25 * speedMultiplier;
        }
        if (arrow.life <= 0) {
          impactArrows.splice(i, 1);
        }
      }

      // Clear canvas
      ctx.clearRect(0, 0, canvas.width, canvas.height);
      ctx.fillStyle = '#f8f9fa';
      ctx.fillRect(0, 0, canvas.width, canvas.height);

      // Draw Runner and UI annotations
      drawRunner(animTime);

      // Draw particle impact push-back force arrows (pointing backward from collision points)
      for (const arrow of impactArrows) {
        const alpha = Math.max(0, arrow.life / arrow.maxLife);
        ctx.save();
        ctx.globalAlpha = alpha;
        drawPointingLeftArrow(arrow.x, arrow.y, arrow.len, '#ef4444', 2.2);
        ctx.restore();
      }

      // Draw Air Particles with smooth transitions
      for (const p of particles) {
        ctx.save();
        // Smooth color transition on collision
        if (p.collided) {
          ctx.fillStyle = p.colorT > 0.4 ? '#93c5fd' : '#3b82f6';
        } else {
          ctx.fillStyle = '#2563eb';
        }

        ctx.beginPath();
        ctx.arc(p.x, p.y, p.radius, 0, Math.PI * 2);
        ctx.fill();

        // Subtle motion trail
        if (!p.collided && speedMode !== 'paused') {
          ctx.strokeStyle = 'rgba(37, 99, 235, 0.25)';
          ctx.lineWidth = 1.5;
          ctx.lineCap = 'round';
          ctx.beginPath();
          ctx.moveTo(p.x, p.y);
          ctx.lineTo(p.x + 5, p.y);
          ctx.stroke();
        }
        ctx.restore();
      }

      requestAnimationFrame(animate);
    }

    requestAnimationFrame(animate);
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Microscopic Friction Diagram</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      -webkit-tap-highlight-color: transparent;
    }

    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      color: #1e2945;
      background: #ffffff;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: flex-start;
      padding: 10px 12px;
      user-select: none;
    }

    .diagram-container {
      width: 100%;
      max-width: 420px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 8px;
    }

    /* Top Section: Macro View without heavy card borders */
    .macro-section {
      width: 100%;
      display: flex;
      flex-direction: column;
      align-items: center;
      position: relative;
    }

    .section-label {
      font-size: 11px;
      font-weight: 700;
      text-transform: uppercase;
      letter-spacing: 0.6px;
      color: #64748b;
      margin-bottom: 4px;
      text-align: center;
    }

    .macro-stage {
      position: relative;
      width: 100%;
      max-width: 320px;
      height: 72px;
    }

    /* Force Arrows in Macro View */
    .macro-arrow {
      position: absolute;
      font-size: 11px;
      font-weight: 800;
      opacity: 0;
      transition: opacity 0.5s ease;
      pointer-events: none;
      z-index: 5;
    }

    .arrow-push {
      top: 4px;
      left: 185px;
      color: #2563eb;
    }

    .arrow-friction {
      top: 46px;
      left: 18px;
      color: #dc2626;
    }

    /* Movable Block */
    .block-macro {
      position: absolute;
      left: 80px;
      top: 6px;
      width: 130px;
      height: 32px;
      background: #d97706;
      border: 1.5px solid #b45309;
      border-radius: 4px;
      display: flex;
      align-items: center;
      justify-content: flex-start;
      padding-left: 14px;
      color: #ffffff;
      font-size: 12px;
      font-weight: 700;
      transition: transform 0.5s cubic-bezier(0.25, 1, 0.5, 1);
      box-shadow: 0 2px 4px rgba(0, 0, 0, 0.08);
      z-index: 2;
    }

    /* Table Base */
    .table-macro {
      position: absolute;
      left: 10px;
      top: 38px;
      width: 300px;
      height: 22px;
      background: #64748b;
      border-top: 1.5px solid #475569;
      border-radius: 3px;
      display: flex;
      align-items: center;
      justify-content: flex-start;
      padding-left: 14px;
      color: #f1f5f9;
      font-size: 11px;
      font-weight: 600;
      z-index: 1;
    }

    /* Focal Zoom Indicator Ring (positioned to avoid overlapping text) */
    .focus-ring {
      position: absolute;
      left: 172px;
      top: 26px;
      width: 26px;
      height: 26px;
      border: 2px dashed #0284c7;
      background: rgba(2, 132, 199, 0.12);
      border-radius: 50%;
      pointer-events: none;
      z-index: 4;
      animation: pulse-ring 2.2s infinite ease-in-out;
    }

    @keyframes pulse-ring {
      0%, 100% { transform: scale(1); opacity: 0.9; }
      50% { transform: scale(1.12); opacity: 0.55; }
    }

    /* Zoom Connector Rays */
    .connector-lines {
      width: 100%;
      max-width: 320px;
      height: 18px;
      position: relative;
    }

    /* Microscopic Zoom View */
    .micro-container {
      width: 100%;
      display: flex;
      flex-direction: column;
      align-items: center;
      position: relative;
    }

    .lens-wrapper {
      position: relative;
      width: 190px;
      height: 190px;
      border-radius: 50%;
      border: 4px solid #0284c7;
      box-shadow: 0 4px 12px rgba(2, 132, 199, 0.15), inset 0 0 10px rgba(0, 0, 0, 0.08);
      background: #ffffff;
      overflow: hidden;
    }

    .lens-glass {
      width: 100%;
      height: 100%;
      display: block;
    }

    .surface-peaks {
      transition: transform 0.5s cubic-bezier(0.25, 1, 0.5, 1);
    }

    /* Collision Markers */
    .spark {
      font-size: 13px;
      fill: #eab308;
      filter: drop-shadow(0 0 3px #facc15);
      animation: twinkle 1.2s infinite alternate ease-in-out;
      transform-origin: center;
    }

    .spark-2 {
      animation-delay: 0.4s;
    }
    .spark-3 {
      animation-delay: 0.8s;
    }

    @keyframes twinkle {
      0% { transform: scale(0.85); opacity: 0.75; }
      100% { transform: scale(1.25); opacity: 1; }
    }

    /* Pedagogical Callout Badge */
    .alert-badge {
      margin-top: 8px;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 20px;
      padding: 5px 12px;
      font-size: 12px;
      font-weight: 700;
      color: #1e2945;
      display: flex;
      align-items: center;
      gap: 6px;
      box-shadow: 0 1px 3px rgba(0, 0, 0, 0.04);
      text-align: center;
    }

    .alert-badge span.star {
      color: #eab308;
      font-size: 14px;
      line-height: 1;
    }

    /* Interactive Controls */
    .controls {
      display: flex;
      gap: 10px;
      margin-top: 6px;
    }

    .btn {
      appearance: none;
      border: 1.5px solid #cbd5e1;
      background: #ffffff;
      color: #1e2945;
      font-size: 12px;
      font-weight: 700;
      padding: 6px 14px;
      border-radius: 6px;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 5px;
      box-shadow: 0 1px 2px rgba(0, 0, 0, 0.04);
      transition: background-color 0.2s, border-color 0.2s, color 0.2s;
    }

    .btn:hover {
      border-color: #94a3b8;
      background: #f8fafc;
    }

    .btn.active {
      background: #0284c7;
      border-color: #0284c7;
      color: #ffffff;
    }

    /* Responsive adjustments */
    @media (max-width: 360px) {
      .lens-wrapper {
        width: 175px;
        height: 175px;
      }
      .macro-stage {
        max-width: 290px;
      }
      .table-macro {
        width: 270px;
      }
      .block-macro {
        width: 115px;
      }
    }
  </style>
</head>
<body>

  <div class="diagram-container">
    
    <div class="macro-section">
      <div class="section-label">Macroscopic View (Appears Smooth & Flat)</div>
      
      <div class="macro-stage">
        
        <div id="pushArrow" class="macro-arrow arrow-push">Push ➔</div>
        <div id="frictArrow" class="macro-arrow arrow-friction">⬅ Friction</div>

        
        <div id="macroBlock" class="block-macro">Wooden Block</div>
        
        <div class="table-macro">Flat Table Surface</div>
        
        
        <div class="focus-ring" title="Zoom region"></div>
      </div>
    </div>

    
    <svg class="connector-lines" viewBox="0 0 320 18" fill="none">
      <line x1="185" y1="0" x2="160" y2="18" stroke="#0284c7" stroke-width="1.5" stroke-dasharray="3 3" opacity="0.6"/>
      <line x1="185" y1="0" x2="160" y2="18" stroke="#0284c7" stroke-width="1.5" stroke-dasharray="3 3" opacity="0.6"/>
    </svg>

    
    <div class="micro-container">
      <div class="section-label">Microscopic Zoom (Interlocking Jagged Peaks)</div>

      <div class="lens-wrapper">
        <svg class="lens-glass" viewBox="0 0 200 200">
          <defs>
            <clipPath id="lensClip">
              <circle cx="100" cy="100" r="95" />
            </clipPath>
          </defs>

          <g clip-path="url(#lensClip)">
            
            <rect width="200" height="200" fill="#f8fafc" />

            
            <path d="M -10,210 L -10,105 
                     L 15,78 L 35,118 L 58,82 L 80,122 L 105,75 L 128,115 L 152,80 L 175,120 L 198,78 L 220,110 
                     L 220,210 Z" 
                  fill="#64748b" stroke="#334155" stroke-width="2" />
            
            <text x="100" y="162" fill="#f1f5f9" font-size="11" font-weight="700" text-anchor="middle">Table Peaks</text>

            
            <g id="microBlockPeaks" class="surface-peaks">
              <path d="M -15,-10 L 225,-10 L 225,90 
                       L 192,118 L 170,82 L 145,120 L 122,80 L 98,122 L 75,78 L 52,116 L 30,76 L 10,118 L -15,85 Z" 
                    fill="#d97706" stroke="#92400e" stroke-width="2" />
              <text x="100" y="44" fill="#ffffff" font-size="11" font-weight="700" text-anchor="middle">Block Peaks</text>
            </g>

            
            <g id="sparkGroup">
              <text x="50" y="106" class="spark spark-1">✦</text>
              <text x="96" y="107" class="spark spark-2">✦</text>
              <text x="143" y="106" class="spark spark-3">✦</text>
            </g>

            
            <circle cx="100" cy="100" r="94" fill="none" stroke="rgba(2,132,199,0.35)" stroke-width="2.5" />
          </g>
        </svg>
      </div>

      
      <div class="alert-badge">
        <span class="star">✦</span>
        <span>Bumps catch and resist movement</span>
      </div>
    </div>

    
    <div class="controls">
      <button id="btnRest" class="btn active" type="button">Resting State</button>
      <button id="btnPush" class="btn" type="button">Push Block ➔</button>
    </div>
  </div>

  <script>
    const btnRest = document.getElementById('btnRest');
    const btnPush = document.getElementById('btnPush');
    const macroBlock = document.getElementById('macroBlock');
    const microBlockPeaks = document.getElementById('microBlockPeaks');
    const pushArrow = document.getElementById('pushArrow');
    const frictArrow = document.getElementById('frictArrow');
    const sparkGroup = document.getElementById('sparkGroup');

    function setPushing(isPushing) {
      if (isPushing) {
        btnPush.classList.add('active');
        btnRest.classList.remove('active');
        
        // Macro movement
        macroBlock.style.transform = 'translateX(18px)';
        pushArrow.style.opacity = '1';
        frictArrow.style.opacity = '1';
        
        // Microscopic interlocking resistance shift
        microBlockPeaks.style.transform = 'translateX(9px)';
        sparkGroup.style.transform = 'scale(1.25)';
        sparkGroup.style.transformOrigin = '100px 100px';
      } else {
        btnRest.classList.add('active');
        btnPush.classList.remove('active');
        
        // Reset positions
        macroBlock.style.transform = 'translateX(0)';
        pushArrow.style.opacity = '0';
        frictArrow.style.opacity = '0';
        
        microBlockPeaks.style.transform = 'translateX(0)';
        sparkGroup.style.transform = 'scale(1)';
      }
    }

    btnRest.addEventListener('click', () => setPushing(false));
    btnPush.addEventListener('click', () => setPushing(true));
  </script>
</body>
</html>

Friction: The Force That Slows Things Down

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    }

    body {
      background: #f8f9fa;
      color: #1e2945;
      padding: 16px;
      display: flex;
      flex-direction: column;
      justify-content: center;
      min-height: 100%;
    }

    .toolbar {
      display: flex;
      justify-content: center;
      margin-bottom: 16px;
    }

    .btn {
      background: #0284c7;
      color: #ffffff;
      border: none;
      padding: 10px 20px;
      font-size: 15px;
      font-weight: 600;
      border-radius: 8px;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 8px;
      box-shadow: 0 2px 4px rgba(0, 0, 0, 0.08);
      transition: background 0.2s, transform 0.1s;
    }

    .btn:active {
      transform: translateY(1px);
    }

    .btn:focus {
      outline: 2px solid #0284c7;
      outline-offset: 2px;
    }

    .tracks {
      display: flex;
      flex-direction: column;
      gap: 16px;
      width: 100%;
    }

    .track-card {
      background: #ffffff;
      border: 1px solid #e6e6e6;
      border-radius: 12px;
      padding: 12px 14px;
      display: flex;
      flex-direction: column;
      gap: 10px;
    }

    .track-header {
      display: flex;
      justify-content: space-between;
      align-items: center;
      font-size: 14px;
      font-weight: 700;
    }

    .meter-box {
      display: flex;
      align-items: center;
      gap: 8px;
      font-size: 13px;
      font-weight: 600;
      color: #4b5563;
    }

    .meter-track {
      width: 70px;
      height: 10px;
      background: #e5e7eb;
      border-radius: 5px;
      overflow: hidden;
      display: flex;
    }

    .meter-fill-ice {
      width: 18%;
      height: 100%;
      background: #0284c7;
      border-radius: 5px;
    }

    .meter-fill-sand {
      width: 90%;
      height: 100%;
      background: #ea580c;
      border-radius: 5px;
    }

    .lane-container {
      position: relative;
      height: 48px;
      border-radius: 8px;
      overflow: hidden;
      border: 1px solid #e6e6e6;
      display: flex;
      align-items: center;
    }

    .lane-ice {
      background: linear-gradient(90deg, #e0f2fe 0%, #bae6fd 100%);
    }

    .lane-sandpaper {
      background: #fef3c7;
      background-image: radial-gradient(#d97706 0.75px, transparent 0.75px), radial-gradient(#d97706 0.75px, #fef3c7 0.75px);
      background-size: 6px 6px;
      background-position: 0 0, 3px 3px;
    }

    .start-line {
      position: absolute;
      left: 12px;
      top: 0;
      bottom: 0;
      width: 3px;
      background: rgba(30, 41, 69, 0.2);
    }

    .finish-line {
      position: absolute;
      right: 12px;
      top: 0;
      bottom: 0;
      width: 6px;
      background: repeating-linear-gradient(
        0deg,
        #1e2945 0px,
        #1e2945 6px,
        #ffffff 6px,
        #ffffff 12px
      );
      opacity: 0.5;
    }

    .car {
      position: absolute;
      top: 50%;
      transform: translateY(-50%);
      left: 6px;
      width: 44px;
      height: 24px;
      z-index: 2;
      transition: left 0.05s linear;
    }

    .car svg {
      width: 100%;
      height: 100%;
      display: block;
      filter: drop-shadow(0 2px 3px rgba(0,0,0,0.18));
    }

    .launched .car-ice {
      left: calc(100% - 50px);
      transition: left 2.6s cubic-bezier(0.12, 0.45, 0.28, 1);
    }

    .launched .car-sand {
      left: 28%;
      transition: left 0.75s cubic-bezier(0.1, 0.85, 0.35, 1);
    }

    .stop-marker {
      position: absolute;
      left: calc(28% + 44px);
      top: 50%;
      transform: translateY(-50%);
      font-size: 11px;
      font-weight: 700;
      color: #ea580c;
      background: #fff;
      padding: 2px 6px;
      border-radius: 4px;
      border: 1px solid #fed7aa;
      opacity: 0;
      transition: opacity 0.3s ease 0.75s;
    }

    .launched .stop-marker {
      opacity: 1;
    }
  </style>
</head>
<body>

  <div class="toolbar">
    <button id="launchBtn" class="btn" onclick="toggleRace()">
      <span id="btnIcon">▶</span>
      <span id="btnText">Launch Cars</span>
    </button>
  </div>

  <div class="tracks" id="trackBox">
    
    
    <div class="track-card">
      <div class="track-header">
        <span>Smooth Ice</span>
        <div class="meter-box">
          <span>Low Friction</span>
          <div class="meter-track">
            <div class="meter-fill-ice"></div>
          </div>
        </div>
      </div>
      <div class="lane-container lane-ice">
        <div class="start-line"></div>
        <div class="finish-line"></div>
        <div class="car car-ice">
          <svg viewBox="0 0 44 24" fill="none" xmlns="http://www.w3.org/2000/svg">
            <rect x="2" y="7" width="38" height="11" rx="4" fill="#ef4444"/>
            <path d="M11 7L16 2H28L33 7H11Z" fill="#dc2626"/>
            <path d="M16 3H22V6H13L16 3Z" fill="#bae6fd"/>
            <path d="M24 3H27L30 6H24V3Z" fill="#bae6fd"/>
            <circle cx="10" cy="18" r="4.5" fill="#1e2945"/>
            <circle cx="10" cy="18" r="2" fill="#9ca3af"/>
            <circle cx="32" cy="18" r="4.5" fill="#1e2945"/>
            <circle cx="32" cy="18" r="2" fill="#9ca3af"/>
            <circle cx="39" cy="11" r="1.5" fill="#fef08a"/>
          </svg>
        </div>
      </div>
    </div>

    
    <div class="track-card">
      <div class="track-header">
        <span>Rough Sandpaper</span>
        <div class="meter-box">
          <span>High Friction</span>
          <div class="meter-track">
            <div class="meter-fill-sand"></div>
          </div>
        </div>
      </div>
      <div class="lane-container lane-sandpaper">
        <div class="start-line"></div>
        <div class="finish-line"></div>
        <div class="stop-marker">Stops!</div>
        <div class="car car-sand">
          <svg viewBox="0 0 44 24" fill="none" xmlns="http://www.w3.org/2000/svg">
            <rect x="2" y="7" width="38" height="11" rx="4" fill="#ef4444"/>
            <path d="M11 7L16 2H28L33 7H11Z" fill="#dc2626"/>
            <path d="M16 3H22V6H13L16 3Z" fill="#bae6fd"/>
            <path d="M24 3H27L30 6H24V3Z" fill="#bae6fd"/>
            <circle cx="10" cy="18" r="4.5" fill="#1e2945"/>
            <circle cx="10" cy="18" r="2" fill="#9ca3af"/>
            <circle cx="32" cy="18" r="4.5" fill="#1e2945"/>
            <circle cx="32" cy="18" r="2" fill="#9ca3af"/>
            <circle cx="39" cy="11" r="1.5" fill="#fef08a"/>
          </svg>
        </div>
      </div>
    </div>

  </div>

  <script>
    let isLaunched = false;

    function toggleRace() {
      const box = document.getElementById('trackBox');
      const btnText = document.getElementById('btnText');
      const btnIcon = document.getElementById('btnIcon');

      if (!isLaunched) {
        box.classList.add('launched');
        btnText.textContent = 'Reset Cars';
        btnIcon.textContent = '↺';
        isLaunched = true;
      } else {
        box.classList.remove('launched');
        btnText.textContent = 'Launch Cars';
        btnIcon.textContent = '▶';
        isLaunched = false;
      }
    }
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Friction on a Sliding Shoe</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }

    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      font-size: 14px;
      color: #1e2945;
      background-color: #f8f9fa;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100vh;
      padding: 12px;
      user-select: none;
    }

    .diagram-container {
      width: 100%;
      max-width: 580px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 16px;
    }

    /* Visual stage with no outer card border */
    .stage {
      position: relative;
      width: 100%;
      height: 280px;
      overflow: hidden;
      background: #ffffff;
      border-radius: 4px;
    }

    /* Wooden Floor */
    .floor {
      position: absolute;
      bottom: 0;
      left: 0;
      width: 100%;
      height: 85px;
      z-index: 1;
      background: #d8a876;
      border-top: 3px solid #8c5828;
      background-image: 
        repeating-linear-gradient(90deg, transparent, transparent 95px, rgba(140, 88, 40, 0.3) 95px, rgba(140, 88, 40, 0.3) 97px),
        linear-gradient(to bottom, #deb07e, #b8814a);
    }

    .floor-label {
      position: absolute;
      bottom: 10px;
      right: 16px;
      font-size: 13px;
      font-weight: 700;
      color: #4a2d14;
      text-transform: uppercase;
      letter-spacing: 0.8px;
    }

    /* Sliding Assembly (Shoe + Arrows) */
    .sliding-group {
      position: absolute;
      bottom: 85px;
      left: 24px;
      width: 175px;
      height: 170px;
      z-index: 10;
      will-change: transform;
    }

    /* Direction of Motion Indicator */
    .motion-indicator {
      position: absolute;
      top: 6px;
      left: 0;
      display: inline-flex;
      align-items: center;
      gap: 8px;
      background: #f0fdf4;
      padding: 5px 10px;
      border-radius: 6px;
      border: 1.5px solid #86efac;
      box-shadow: 0 1px 3px rgba(0, 0, 0, 0.06);
      white-space: nowrap;
    }

    .motion-label {
      font-size: 14px;
      font-weight: 700;
      color: #15803d;
    }

    .motion-arrow-svg {
      width: 36px;
      height: 16px;
      flex-shrink: 0;
    }

    /* Sneaker */
    .sneaker-svg {
      position: absolute;
      bottom: 0;
      left: 0;
      width: 170px;
      height: 96px;
      filter: drop-shadow(0 4px 5px rgba(0, 0, 0, 0.18));
    }

    /* Opposing Friction Arrow at Contact Boundary */
    .friction-indicator {
      position: absolute;
      bottom: -18px;
      left: 8px;
      display: inline-flex;
      align-items: center;
      gap: 8px;
      background: #ffffff;
      padding: 5px 12px;
      border-radius: 6px;
      border: 2px solid #dc2626;
      box-shadow: 0 3px 8px rgba(220, 38, 38, 0.25);
      z-index: 20;
      white-space: nowrap;
    }

    .friction-arrow-svg {
      width: 36px;
      height: 16px;
      flex-shrink: 0;
    }

    .friction-label {
      font-size: 14px;
      font-weight: 800;
      color: #b91c1c;
      text-transform: uppercase;
      letter-spacing: 0.5px;
    }

    /* Pulsing friction animation during movement */
    .pulsing .friction-indicator {
      animation: frictionActive 0.3s ease-in-out infinite alternate;
    }

    @keyframes frictionActive {
      0% {
        background: #fee2e2;
        border-color: #ef4444;
        box-shadow: 0 0 6px rgba(220, 38, 38, 0.5);
      }
      100% {
        background: #fca5a5;
        border-color: #991b1b;
        box-shadow: 0 0 14px rgba(220, 38, 38, 0.85);
      }
    }

    /* Controls Bar */
    .controls {
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 10px;
      width: 100%;
    }

    .btn {
      appearance: none;
      border: none;
      background: #1e2945;
      color: #ffffff;
      font-family: inherit;
      font-size: 14px;
      font-weight: 600;
      padding: 10px 24px;
      border-radius: 6px;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 8px;
      transition: background-color 0.2s, opacity 0.2s;
    }

    .btn:hover {
      background: #2d3d66;
    }

    .btn:active {
      background: #161e33;
    }

    .caption {
      font-size: 14px;
      color: #1e2945;
      text-align: center;
      line-height: 1.4;
    }

    @media (max-width: 440px) {
      .sliding-group {
        left: 12px;
      }
      .motion-label, .friction-label {
        font-size: 13px;
      }
      .stage {
        height: 270px;
      }
    }
  </style>
</head>
<body>

  <div class="diagram-container">
    <div class="stage">
      
      
      <div id="slidingGroup" class="sliding-group">
        
        
        <div class="motion-indicator">
          <span class="motion-label">Direction of Motion</span>
          <svg class="motion-arrow-svg" viewBox="0 0 36 16" fill="none">
            <line x1="2" y1="8" x2="26" y2="8" stroke="#16a34a" stroke-width="3.5" stroke-linecap="round"/>
            <polygon points="24,3 34,8 24,13" fill="#16a34a"/>
          </svg>
        </div>

        
        <svg class="sneaker-svg" viewBox="0 0 170 96">
          
          <path d="M 28 68 Q 22 42 48 37 Q 75 34 85 50 Q 100 40 128 50 Q 155 60 162 73 L 16 73 Q 20 70 28 68 Z" fill="#2563eb"/>
          
          <path d="M 16 73 Q 20 48 38 40 L 44 58 Q 27 63 16 73 Z" fill="#1d4ed8"/>
          
          <path d="M 48 37 Q 58 19 72 21 Q 80 32 83 42 Z" fill="#3b82f6"/>
          <path d="M 72 21 Q 88 23 94 40 L 83 45 Z" fill="#60a5fa"/>
          
          <path d="M 77 36 L 94 44 M 82 44 L 101 52 M 90 52 L 112 58" stroke="#ffffff" stroke-width="3" stroke-linecap="round"/>
          
          <path d="M 40 60 Q 80 65 128 52 Q 90 71 40 60 Z" fill="#ffffff" opacity="0.95"/>
          
          <path d="M 138 56 Q 158 63 162 73 L 130 73 Q 128 62 138 56 Z" fill="#1d4ed8"/>
          
          <path d="M 10 73 L 165 73 Q 168 78 164 86 L 12 86 Q 8 78 10 73 Z" fill="#ffffff"/>
          <path d="M 10 80 L 165 80" stroke="#e2e8f0" stroke-width="1.5"/>
          
          <path d="M 12 86 L 164 86 L 162 92 L 14 92 Z" fill="#1e293b"/>
          
          <line x1="28" y1="89" x2="40" y2="89" stroke="#94a3b8" stroke-width="2.5" stroke-linecap="round"/>
          <line x1="55" y1="89" x2="72" y2="89" stroke="#94a3b8" stroke-width="2.5" stroke-linecap="round"/>
          <line x1="88" y1="89" x2="105" y2="89" stroke="#94a3b8" stroke-width="2.5" stroke-linecap="round"/>
          <line x1="120" y1="89" x2="136" y2="89" stroke="#94a3b8" stroke-width="2.5" stroke-linecap="round"/>
          <line x1="146" y1="89" x2="156" y2="89" stroke="#94a3b8" stroke-width="2.5" stroke-linecap="round"/>
        </svg>

        
        <div class="friction-indicator">
          <svg class="friction-arrow-svg" viewBox="0 0 36 16" fill="none">
            <polygon points="12,3 2,8 12,13" fill="#dc2626"/>
            <line x1="10" y1="8" x2="34" y2="8" stroke="#dc2626" stroke-width="3.5" stroke-linecap="round"/>
          </svg>
          <span class="friction-label">Friction</span>
        </div>

      </div>

      
      <div class="floor">
        <span class="floor-label">Wood Floor</span>
      </div>

    </div>

    
    <div class="controls">
      <button id="pushBtn" class="btn" onclick="triggerPush()">
        <span>Push Shoe</span>
        <span>▶</span>
      </button>
      <div class="caption">Friction acts at the contact boundary between the sole and the floor, opposing forward motion.</div>
    </div>
  </div>

  <script>
    let isMoving = false;
    const slidingGroup = document.getElementById('slidingGroup');
    const pushBtn = document.getElementById('pushBtn');

    function triggerPush() {
      if (isMoving) return;
      isMoving = true;

      const stage = document.querySelector('.stage');
      const maxSlide = Math.min(190, stage.clientWidth - 220);

      // Reset instantly to beginning
      slidingGroup.style.transition = 'none';
      slidingGroup.style.transform = 'translateX(0px)';
      slidingGroup.classList.remove('pulsing');
      pushBtn.disabled = true;
      pushBtn.style.opacity = '0.5';
      pushBtn.style.cursor = 'default';

      // Animate sliding and decelerating
      requestAnimationFrame(() => {
        requestAnimationFrame(() => {
          slidingGroup.style.transition = 'transform 1.6s cubic-bezier(0.12, 0.8, 0.3, 1)';
          slidingGroup.style.transform = `translateX(${Math.max(90, maxSlide)}px)`;
          slidingGroup.classList.add('pulsing');

          setTimeout(() => {
            slidingGroup.classList.remove('pulsing');
            setTimeout(() => {
              isMoving = false;
              pushBtn.disabled = false;
              pushBtn.style.opacity = '1';
              pushBtn.style.cursor = 'pointer';
            }, 250);
          }, 1600);
        });
      });
    }
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <title>Air vs Water Resistance</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      user-select: none;
      -webkit-user-select: none;
    }
    body {
      width: 100%;
      height: 100%;
      background: #f8fafc;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      padding: 12px;
      overflow: hidden;
    }
    .header-row {
      width: 100%;
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 12px;
      margin-bottom: 8px;
    }
    .chamber-header {
      display: flex;
      align-items: center;
      justify-content: space-between;
      padding: 6px 14px;
      border-radius: 8px;
      font-weight: 700;
      font-size: 15px;
    }
    .header-air {
      background: #e0f2fe;
      color: #0369a1;
      border: 1px solid #bae6fd;
    }
    .header-water {
      background: #dbeafe;
      color: #1d4ed8;
      border: 1px solid #bfdbfe;
    }
    .tag {
      font-size: 12px;
      font-weight: 600;
      padding: 2px 8px;
      border-radius: 12px;
    }
    .tag-air {
      background: rgba(3, 105, 161, 0.1);
      color: #0284c7;
    }
    .tag-water {
      background: rgba(29, 78, 216, 0.15);
      color: #1e40af;
    }
    .canvas-container {
      width: 100%;
      flex: 1;
      min-height: 220px;
      position: relative;
      border-radius: 12px;
      overflow: hidden;
      box-shadow: 0 2px 8px rgba(0, 0, 0, 0.04);
      background: #fff;
    }
    canvas {
      width: 100%;
      height: 100%;
      display: block;
    }
    .controls {
      width: 100%;
      display: flex;
      justify-content: center;
      gap: 12px;
      margin-top: 10px;
    }
    .btn {
      appearance: none;
      border: none;
      background: #2563eb;
      color: #ffffff;
      font-weight: 600;
      font-size: 14px;
      padding: 10px 24px;
      border-radius: 20px;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 6px;
      box-shadow: 0 2px 6px rgba(37, 99, 235, 0.3);
      transition: background 0.2s, opacity 0.2s;
    }
    .btn:active {
      background: #1d4ed8;
    }
    .btn.reset {
      background: #64748b;
      box-shadow: 0 2px 6px rgba(100, 116, 139, 0.25);
    }
    .btn.reset:active {
      background: #475569;
    }
  </style>
</head>
<body>

  <div class="header-row">
    <div class="chamber-header header-air">
      <span>💨 Air</span>
      <span class="tag tag-air">Low Density</span>
    </div>
    <div class="chamber-header header-water">
      <span>💧 Water</span>
      <span class="tag tag-water">High Density</span>
    </div>
  </div>

  <div class="canvas-container" id="container">
    <canvas id="simCanvas"></canvas>
  </div>

  <div class="controls">
    <button class="btn" id="actionBtn">
      <span id="btnIcon">▶</span>
      <span id="btnLabel">Push Hand</span>
    </button>
  </div>

  <script>
    const canvas = document.getElementById('simCanvas');
    const ctx = canvas.getContext('2d');
    const container = document.getElementById('container');
    const actionBtn = document.getElementById('actionBtn');
    const btnIcon = document.getElementById('btnIcon');
    const btnLabel = document.getElementById('btnLabel');

    let width, height;
    let animProgress = 0; // 0 = start, 1 = fully pushed
    let state = 'idle'; // 'idle', 'moving', 'done'
    
    const airParticles = [];
    const waterParticles = [];
    const NUM_AIR = 18;
    const NUM_WATER = 260;

    function resize() {
      const dpr = window.devicePixelRatio || 1;
      const rect = container.getBoundingClientRect();
      width = rect.width;
      height = rect.height;
      canvas.width = width * dpr;
      canvas.height = height * dpr;
      ctx.resetTransform();
      ctx.scale(dpr, dpr);
      initParticles();
    }

    function initParticles() {
      airParticles.length = 0;
      waterParticles.length = 0;
      const halfW = width / 2;

      // Air particles (widely spaced)
      for (let i = 0; i < NUM_AIR; i++) {
        airParticles.push({
          x: 20 + Math.random() * (halfW - 50),
          y: 20 + Math.random() * (height - 40),
          vx: (Math.random() - 0.5) * 0.4,
          vy: (Math.random() - 0.5) * 0.4,
          r: 5
        });
      }

      // Water particles (closely packed grid with small jitter)
      const cols = 15;
      const rows = Math.round(NUM_WATER / cols);
      const spacingX = (halfW - 40) / cols;
      const spacingY = (height - 30) / rows;

      for (let r = 0; r < rows; r++) {
        for (let c = 0; c < cols; c++) {
          const originX = halfW + 20 + c * spacingX + (Math.random() - 0.5) * 4;
          const originY = 15 + r * spacingY + (Math.random() - 0.5) * 4;
          waterParticles.push({
            x: originX,
            y: originY,
            origX: originX,
            origY: originY,
            vx: (Math.random() - 0.5) * 0.2,
            vy: (Math.random() - 0.5) * 0.2,
            r: 4.5
          });
        }
      }
    }

    function drawHand(x, y, isWater) {
      ctx.save();
      ctx.translate(x, y);

      // Hand palm & fingers
      ctx.fillStyle = '#fbcfe8';
      ctx.strokeStyle = '#f472b6';
      ctx.lineWidth = 2;

      // Draw stylized pushing hand palm facing right
      ctx.beginPath();
      ctx.roundRect(-24, -22, 26, 44, 8);
      ctx.fill();
      ctx.stroke();

      // Fingers
      for (let i = -16; i <= 16; i += 10) {
        ctx.beginPath();
        ctx.roundRect(2, i - 4, 14, 8, 4);
        ctx.fill();
        ctx.stroke();
      }

      // Thumb
      ctx.beginPath();
      ctx.roundRect(-10, -32, 10, 14, 5);
      ctx.fill();
      ctx.stroke();

      // Force arrows
      if (animProgress > 0.05) {
        if (!isWater) {
          // Minimal drag arrow in air
          ctx.fillStyle = '#94a3b8';
          ctx.strokeStyle = '#94a3b8';
          ctx.lineWidth = 1.5;
          ctx.beginPath();
          ctx.moveTo(-32, 0);
          ctx.lineTo(-44, 0);
          ctx.stroke();
          // Arrowhead
          ctx.beginPath();
          ctx.moveTo(-44, 0);
          ctx.lineTo(-39, -4);
          ctx.lineTo(-39, 4);
          ctx.closePath();
          ctx.fill();

          ctx.font = '600 11px system-ui';
          ctx.fillStyle = '#64748b';
          ctx.textAlign = 'right';
          ctx.fillText('Low Drag', -48, 4);
        } else {
          // Large Drag Force in water
          const arrowLen = Math.min(65, animProgress * 80);
          ctx.strokeStyle = '#dc2626';
          ctx.fillStyle = '#dc2626';
          ctx.lineWidth = 3.5;
          ctx.beginPath();
          ctx.moveTo(-32, 0);
          ctx.lineTo(-32 - arrowLen, 0);
          ctx.stroke();

          // Arrowhead
          ctx.beginPath();
          ctx.moveTo(-32 - arrowLen - 4, 0);
          ctx.lineTo(-32 - arrowLen + 6, -6);
          ctx.lineTo(-32 - arrowLen + 6, 6);
          ctx.closePath();
          ctx.fill();

          ctx.font = '700 12px system-ui';
          ctx.fillStyle = '#b91c1c';
          ctx.textAlign = 'right';
          ctx.fillText('Drag Force', -40 - arrowLen, 4);
        }
      }

      ctx.restore();
    }

    function render() {
      ctx.clearRect(0, 0, width, height);
      const halfW = width / 2;

      // Divider line
      ctx.strokeStyle = '#e2e8f0';
      ctx.lineWidth = 2;
      ctx.setLineDash([6, 6]);
      ctx.beginPath();
      ctx.moveTo(halfW, 0);
      ctx.lineTo(halfW, height);
      ctx.stroke();
      ctx.setLineDash([]);

      // Water background tint
      ctx.fillStyle = 'rgba(239, 246, 255, 0.6)';
      ctx.fillRect(halfW, 0, halfW, height);

      // Hand X positions based on progress
      const handStartX = 45;
      const handEndX = halfW - 40;
      const airHandX = handStartX + animProgress * (handEndX - handStartX);
      const waterHandX = halfW + handStartX + animProgress * (handEndX - handStartX);
      const handY = height / 2;

      // --- AIR PARTICLES ---
      ctx.fillStyle = '#38bdf8';
      ctx.strokeStyle = '#0284c7';
      ctx.lineWidth = 1;

      for (const p of airParticles) {
        // Slow float
        p.x += p.vx;
        p.y += p.vy;
        if (p.x < 10 || p.x > halfW - 10) p.vx *= -1;
        if (p.y < 10 || p.y > height - 10) p.vy *= -1;

        // Push away slightly if hand moves near
        const dx = p.x - airHandX;
        const dy = p.y - handY;
        const dist = Math.hypot(dx, dy);
        if (dist < 32 && animProgress > 0) {
          p.x += (dx / (dist || 1)) * 3;
          p.y += (dy / (dist || 1)) * 3;
        }

        ctx.beginPath();
        ctx.arc(p.x, p.y, p.r, 0, Math.PI * 2);
        ctx.fill();
        ctx.stroke();
      }

      // --- WATER PARTICLES ---
      ctx.fillStyle = '#2563eb';
      ctx.strokeStyle = '#1d4ed8';
      ctx.lineWidth = 1;

      for (const p of waterParticles) {
        // Gentle liquid jitter
        p.x += p.vx;
        p.y += p.vy;
        if (Math.abs(p.x - p.origX) > 4) p.vx *= -1;
        if (Math.abs(p.y - p.origY) > 4) p.vy *= -1;

        // Severe compression & collision wall in front of pushing hand
        if (animProgress > 0) {
          const dx = p.x - (waterHandX + 12);
          const dy = p.y - handY;
          const dist = Math.hypot(dx, dy);

          if (dx > -20 && dx < 50 && Math.abs(dy) < 42) {
            // Compress into tight wall directly in front
            const pushDist = 48 - dx;
            p.x += pushDist * 0.4;
            p.y += (dy > 0 ? 1 : -1) * 0.8;
          }
        }

        ctx.beginPath();
        ctx.arc(p.x, p.y, p.r, 0, Math.PI * 2);
        ctx.fill();
        ctx.stroke();
      }

      // Draw hands
      drawHand(airHandX, handY, false);
      drawHand(waterHandX, handY, true);

      // Animate progress
      if (state === 'moving') {
        animProgress += 0.008;
        if (animProgress >= 1) {
          animProgress = 1;
          state = 'done';
          btnIcon.textContent = '↺';
          btnLabel.textContent = 'Reset';
          actionBtn.classList.add('reset');
        }
      }

      requestAnimationFrame(render);
    }

    actionBtn.addEventListener('click', () => {
      if (state === 'idle') {
        state = 'moving';
        btnIcon.textContent = '⏳';
        btnLabel.textContent = 'Pushing...';
      } else if (state === 'done') {
        animProgress = 0;
        state = 'idle';
        initParticles();
        btnIcon.textContent = '▶';
        btnLabel.textContent = 'Push Hand';
        actionBtn.classList.remove('reset');
      }
    });

    window.addEventListener('resize', resize);
    resize();
    render();
  </script>
</body>
</html>

Water Resistance: Pushing Against Movement

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      color: #1e2945;
      background: transparent;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      padding: 12px;
      gap: 12px;
      min-height: 100%;
    }

    .panels {
      display: flex;
      gap: 12px;
      width: 100%;
      max-width: 600px;
    }

    .tank {
      flex: 1;
      height: 240px;
      background: linear-gradient(180deg, #e0f2fe 0%, #bae6fd 100%);
      border-radius: 12px;
      border: 1px solid #7dd3fc;
      position: relative;
      overflow: hidden;
      display: flex;
      align-items: center;
      justify-content: center;
    }

    .water-line {
      position: absolute;
      top: 0;
      left: 0;
      right: 0;
      height: 6px;
      background: rgba(255, 255, 255, 0.6);
    }

    /* Submarine styles */
    .sub-wrap {
      position: absolute;
      transition: transform 0.4s ease;
    }
    .sub-hull {
      width: 80px;
      height: 38px;
      background: #facc15;
      border: 2px solid #ca8a04;
      border-radius: 20px;
      position: relative;
    }
    .sub-window {
      position: absolute;
      width: 12px;
      height: 12px;
      background: #38bdf8;
      border: 2px solid #0284c7;
      border-radius: 50%;
      top: 11px;
      left: 48px;
    }
    .sub-tower {
      position: absolute;
      width: 16px;
      height: 14px;
      background: #eab308;
      border: 2px solid #ca8a04;
      border-bottom: none;
      top: -12px;
      left: 32px;
      border-radius: 4px 4px 0 0;
    }
    .sub-prop {
      position: absolute;
      width: 6px;
      height: 18px;
      background: #94a3b8;
      top: 10px;
      left: -6px;
      border-radius: 2px;
    }

    /* Coin styles */
    .coin {
      width: 46px;
      height: 46px;
      background: radial-gradient(circle at 35% 35%, #fde047, #ca8a04);
      border: 2px solid #a16207;
      border-radius: 50%;
      display: flex;
      align-items: center;
      justify-content: center;
      font-weight: 800;
      font-size: 18px;
      color: #78350f;
      box-shadow: inset 0 0 0 2px #fef08a, 0 2px 4px rgba(0,0,0,0.1);
    }

    /* Force Arrows */
    .arrow-container {
      position: absolute;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      transition: transform 0.4s ease;
      pointer-events: none;
    }

    .arrow-badge {
      font-size: 11px;
      font-weight: 700;
      padding: 3px 8px;
      border-radius: 12px;
      white-space: nowrap;
    }

    /* Horizontal Tank Arrow Positions */
    .tank-h .arrow-motion {
      top: 32px;
      left: 50%;
      transform: translateX(-50%);
    }
    .tank-h .arrow-drag {
      bottom: 32px;
      left: 50%;
      transform: translateX(-50%);
    }

    /* Vertical Tank Arrow Positions */
    .tank-v .arrow-motion {
      right: 12px;
      top: 50%;
      transform: translateY(-50%);
      flex-direction: column;
    }
    .tank-v .arrow-drag {
      left: 12px;
      top: 50%;
      transform: translateY(-50%);
      flex-direction: column;
    }

    .badge-green {
      background: #dcfce7;
      color: #15803d;
      border: 1px solid #86efac;
    }
    .badge-red {
      background: #fee2e2;
      color: #b91c1c;
      border: 1px solid #fca5a5;
    }

    .arrow-svg {
      transition: transform 0.4s ease;
    }

    /* Button */
    .swap-btn {
      background: #0284c7;
      color: #ffffff;
      border: none;
      border-radius: 20px;
      padding: 8px 18px;
      font-size: 14px;
      font-weight: 600;
      cursor: pointer;
      display: flex;
      align-items: center;
      gap: 6px;
      box-shadow: 0 2px 4px rgba(2, 132, 199, 0.25);
      transition: background-color 0.2s, box-shadow 0.2s;
    }
    .swap-btn:active {
      background: #0369a1;
      box-shadow: none;
    }
  </style>
</head>
<body>

  <div class="panels">
    
    <div class="tank tank-h">
      <div class="water-line"></div>
      
      
      <div class="arrow-container arrow-motion">
        <span class="arrow-badge badge-green">Motion</span>
        <svg id="arrow-sub-motion" class="arrow-svg" width="36" height="18" viewBox="0 0 36 18">
          <path d="M2 9 L28 9 M22 3 L28 9 L22 15" fill="none" stroke="#16a34a" stroke-width="3.5" stroke-linecap="round" stroke-linejoin="round"/>
        </svg>
      </div>

      
      <div id="sub" class="sub-wrap">
        <div class="sub-hull">
          <div class="sub-tower"></div>
          <div class="sub-window"></div>
          <div class="sub-prop"></div>
        </div>
      </div>

      
      <div class="arrow-container arrow-drag">
        <svg id="arrow-sub-drag" class="arrow-svg" width="36" height="18" viewBox="0 0 36 18">
          <path d="M34 9 L8 9 M14 3 L8 9 L14 15" fill="none" stroke="#dc2626" stroke-width="3.5" stroke-linecap="round" stroke-linejoin="round"/>
        </svg>
        <span class="arrow-badge badge-red">Water Resistance</span>
      </div>
    </div>

    
    <div class="tank tank-v">
      <div class="water-line"></div>

      
      <div class="arrow-container arrow-drag">
        <span class="arrow-badge badge-red">Water Resistance</span>
        <svg id="arrow-coin-drag" class="arrow-svg" width="18" height="36" viewBox="0 0 18 36">
          <path d="M9 34 L9 8 M3 14 L9 8 L15 14" fill="none" stroke="#dc2626" stroke-width="3.5" stroke-linecap="round" stroke-linejoin="round"/>
        </svg>
      </div>

      
      <div class="coin">1p</div>

      
      <div class="arrow-container arrow-motion">
        <svg id="arrow-coin-motion" class="arrow-svg" width="18" height="36" viewBox="0 0 18 36">
          <path d="M9 2 L9 28 M3 22 L9 28 L15 22" fill="none" stroke="#16a34a" stroke-width="3.5" stroke-linecap="round" stroke-linejoin="round"/>
        </svg>
        <span class="arrow-badge badge-green">Motion</span>
      </div>
    </div>
  </div>

  <button class="swap-btn" id="swapBtn">
    <span>Swap Direction</span>
    <span style="font-size: 16px;">⇄</span>
  </button>

  <script>
    let reversed = false;

    const sub = document.getElementById('sub');
    const arrowSubMotion = document.getElementById('arrow-sub-motion');
    const arrowSubDrag = document.getElementById('arrow-sub-drag');
    const arrowCoinMotion = document.getElementById('arrow-coin-motion');
    const arrowCoinDrag = document.getElementById('arrow-coin-drag');
    const swapBtn = document.getElementById('swapBtn');

    swapBtn.addEventListener('click', () => {
      reversed = !reversed;

      if (reversed) {
        // Submarine flips left, motion left, drag right
        sub.style.transform = 'scaleX(-1)';
        arrowSubMotion.style.transform = 'scaleX(-1)';
        arrowSubDrag.style.transform = 'scaleX(-1)';

        // Coin motion up, drag down
        arrowCoinMotion.style.transform = 'scaleY(-1)';
        arrowCoinDrag.style.transform = 'scaleY(-1)';
      } else {
        // Normal states
        sub.style.transform = 'scaleX(1)';
        arrowSubMotion.style.transform = 'scaleX(1)';
        arrowSubDrag.style.transform = 'scaleX(1)';

        arrowCoinMotion.style.transform = 'scaleY(1)';
        arrowCoinDrag.style.transform = 'scaleY(1)';
      }
    });
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }

    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: transparent;
      color: #0f172a;
      padding: 10px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: flex-start;
      min-height: 100vh;
      box-sizing: border-box;
    }

    .container {
      width: 100%;
      max-width: 680px;
      display: flex;
      flex-direction: column;
      gap: 10px;
    }

    /* Panels Layout */
    .panels {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 10px;
      width: 100%;
    }

    @media (max-width: 480px) {
      .panels {
        grid-template-columns: 1fr;
        gap: 8px;
      }
    }

    .panel {
      background: #ffffff;
      border: 1px solid #cbd5e1;
      border-radius: 10px;
      display: flex;
      flex-direction: column;
      align-items: center;
      padding: 8px 6px 6px;
      position: relative;
      overflow: hidden;
    }

    .panel-header {
      display: flex;
      align-items: center;
      justify-content: space-between;
      width: 100%;
      padding: 0 4px 4px;
      border-bottom: 1px solid #f1f5f9;
    }

    .panel-title {
      font-size: 13px;
      font-weight: 700;
      color: #1e293b;
    }

    .panel-tag {
      font-size: 11px;
      font-weight: 600;
      padding: 2px 6px;
      border-radius: 4px;
    }

    .tag-air {
      background: #f1f5f9;
      color: #475569;
    }

    .tag-water {
      background: #e0f2fe;
      color: #0369a1;
    }

    .scene {
      width: 100%;
      height: 185px;
      position: relative;
    }

    @media (max-width: 480px) {
      .scene {
        height: 165px;
      }
    }

    svg {
      width: 100%;
      height: 100%;
      display: block;
    }

    /* Force Arrows & Badges */
    .force-group {
      transition: opacity 0.5s ease, filter 0.5s ease;
    }

    .highlight-force .drag-highlight {
      filter: drop-shadow(0 0 5px rgba(220, 38, 38, 0.7));
    }

    .highlight-force .badge-drag {
      stroke-width: 2px;
      stroke: #dc2626;
    }

    /* Controls */
    .controls {
      display: flex;
      gap: 8px;
      width: 100%;
      justify-content: center;
    }

    .btn {
      flex: 1;
      max-width: 240px;
      padding: 8px 12px;
      border-radius: 6px;
      border: 1px solid #cbd5e1;
      background: #ffffff;
      color: #334155;
      font-size: 12px;
      font-weight: 600;
      cursor: pointer;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      transition: background-color 0.5s ease, border-color 0.5s ease, color 0.5s ease;
    }

    .btn:hover {
      background: #f8fafc;
      border-color: #94a3b8;
    }

    .btn.active {
      background: #eff6ff;
      border-color: #2563eb;
      color: #1d4ed8;
    }

    /* Animation Styles - smooth and safe intervals */
    .running-body {
      animation: runnerBob 1.2s infinite ease-in-out alternate;
      transform-origin: center bottom;
    }

    @keyframes runnerBob {
      0% { transform: translateY(0px); }
      100% { transform: translateY(-3px); }
    }

    .ripple-circle {
      animation: rippleSpread 2.4s infinite ease-out;
      transform-origin: 130px 118px;
      opacity: 0;
    }

    .ripple-delayed {
      animation-delay: 1.2s;
    }

    @keyframes rippleSpread {
      0% {
        r: 4px;
        opacity: 0.85;
        stroke-width: 2px;
      }
      70% {
        opacity: 0.35;
      }
      100% {
        r: 32px;
        opacity: 0;
        stroke-width: 0.5px;
      }
    }

    #ripplesLayer {
      transition: opacity 0.5s ease;
    }

    .submerged-leg {
      opacity: 0.75;
    }
  </style>
</head>
<body>

  <div class="container" id="mainContainer">
    <div class="panels highlight-force" id="panelsWrapper">
      
      
      <div class="panel">
        <div class="panel-header">
          <span class="panel-title">Running in Air</span>
          <span class="panel-tag tag-air">Low Drag</span>
        </div>
        <div class="scene">
          <svg viewBox="0 0 240 190" preserveAspectRatio="xMidYMid meet">
            
            <line x1="10" y1="168" x2="230" y2="168" stroke="#94a3b8" stroke-width="3" stroke-linecap="round" />
            <line x1="15" y1="176" x2="225" y2="176" stroke="#cbd5e1" stroke-width="2" stroke-dasharray="8 6" />

            
            <path d="M 40 70 Q 25 70 15 75" stroke="#cbd5e1" stroke-width="1.5" fill="none" stroke-linecap="round" />
            <path d="M 48 92 Q 30 92 20 98" stroke="#cbd5e1" stroke-width="1.5" fill="none" stroke-linecap="round" />
            <path d="M 38 115 Q 22 115 15 120" stroke="#cbd5e1" stroke-width="1.5" fill="none" stroke-linecap="round" />

            
            <g class="running-body">
              
              <path d="M 130 75 L 110 88 L 102 78" fill="none" stroke="#64748b" stroke-width="4.5" stroke-linecap="round" stroke-linejoin="round" />
              
              <path d="M 134 110 L 108 138 L 92 162" fill="none" stroke="#475569" stroke-width="5.5" stroke-linecap="round" stroke-linejoin="round" />
              
              <path d="M 134 110 L 154 136 L 168 168" fill="none" stroke="#1e293b" stroke-width="5.5" stroke-linecap="round" stroke-linejoin="round" />
              
              <line x1="130" y1="68" x2="134" y2="110" stroke="#1e293b" stroke-width="7" stroke-linecap="round" />
              
              <circle cx="130" cy="54" r="12" fill="#2563eb" />
              
              <path d="M 130 75 L 148 88 L 160 76" fill="none" stroke="#1e293b" stroke-width="4.5" stroke-linecap="round" stroke-linejoin="round" />
            </g>

            
            <g class="force-group">
              <rect x="135" y="10" width="85" height="18" rx="4" fill="#f0fdf4" stroke="#86efac" stroke-width="1" />
              <text x="177" y="23" text-anchor="middle" font-size="10" font-weight="700" fill="#15803d">Motion (Forward)</text>
              <line x1="135" y1="34" x2="200" y2="34" stroke="#16a34a" stroke-width="3" stroke-linecap="round" />
              <polygon points="208,34 198,29 198,39" fill="#16a34a" />
            </g>

            
            <g class="force-group drag-highlight" id="airDragGroup">
              <rect x="12" y="38" width="90" height="18" rx="4" fill="#fff" stroke="#fca5a5" stroke-width="1" class="badge-drag" />
              <text x="57" y="51" text-anchor="middle" font-size="9.5" font-weight="700" fill="#b91c1c">Air Resistance</text>
              <line x1="112" y1="60" x2="72" y2="60" stroke="#dc2626" stroke-width="2" stroke-linecap="round" />
              <polygon points="64,60 74,56 74,64" fill="#dc2626" />
              <text x="57" y="74" text-anchor="middle" font-size="8.5" font-weight="600" fill="#dc2626">(Tiny Force)</text>
            </g>
          </svg>
        </div>
      </div>

      
      <div class="panel">
        <div class="panel-header">
          <span class="panel-title">Running in Water</span>
          <span class="panel-tag tag-water">Huge Drag</span>
        </div>
        <div class="scene">
          <svg viewBox="0 0 240 190" preserveAspectRatio="xMidYMid meet">
            
            <line x1="10" y1="168" x2="230" y2="168" stroke="#0284c7" stroke-width="3" stroke-linecap="round" />
            <line x1="15" y1="176" x2="225" y2="176" stroke="#7dd3fc" stroke-width="2" stroke-dasharray="8 6" />

            
            <g id="ripplesLayer" opacity="0">
              <ellipse cx="130" cy="118" rx="14" ry="4" fill="none" stroke="#38bdf8" class="ripple-circle" />
              <ellipse cx="130" cy="118" rx="22" ry="6" fill="none" stroke="#0284c7" class="ripple-circle ripple-delayed" />
            </g>

            
            <g class="running-body">
              
              <path d="M 130 75 L 110 88 L 102 78" fill="none" stroke="#64748b" stroke-width="4.5" stroke-linecap="round" stroke-linejoin="round" />
              
              <path d="M 134 110 L 108 138 L 92 162" fill="none" stroke="#334155" stroke-width="5.5" stroke-linecap="round" stroke-linejoin="round" class="submerged-leg" />
              
              <path d="M 134 110 L 154 136 L 168 168" fill="none" stroke="#0f172a" stroke-width="5.5" stroke-linecap="round" stroke-linejoin="round" class="submerged-leg" />
              
              <line x1="130" y1="68" x2="134" y2="110" stroke="#1e293b" stroke-width="7" stroke-linecap="round" />
              
              <circle cx="130" cy="54" r="12" fill="#2563eb" />
              
              <path d="M 130 75 L 148 88 L 160 76" fill="none" stroke="#1e293b" stroke-width="4.5" stroke-linecap="round" stroke-linejoin="round" />
            </g>

            
            <rect x="0" y="118" width="240" height="50" fill="#0284c7" fill-opacity="0.22" />
            
            <path d="M 0 118 Q 30 115, 60 118 T 120 118 T 180 118 T 240 118" fill="none" stroke="#0284c7" stroke-width="2.5" />

            
            <circle cx="118" cy="112" r="2.5" fill="#38bdf8" />
            <circle cx="146" cy="110" r="3" fill="#38bdf8" />
            <circle cx="156" cy="115" r="2" fill="#0284c7" />

            
            <g class="force-group">
              <rect x="135" y="10" width="85" height="18" rx="4" fill="#f0fdf4" stroke="#86efac" stroke-width="1" />
              <text x="177" y="23" text-anchor="middle" font-size="10" font-weight="700" fill="#15803d">Motion (Forward)</text>
              <line x1="135" y1="34" x2="200" y2="34" stroke="#16a34a" stroke-width="3" stroke-linecap="round" />
              <polygon points="208,34 198,29 198,39" fill="#16a34a" />
            </g>

            
            <g class="force-group drag-highlight" id="waterDragGroup">
              
              <rect x="8" y="94" width="108" height="19" rx="4" fill="#ffffff" stroke="#ef4444" stroke-width="1.5" class="badge-drag" />
              <text x="62" y="108" text-anchor="middle" font-size="9.5" font-weight="700" fill="#b91c1c">Water Drag (Huge!)</text>
              
              
              <line x1="124" y1="142" x2="42" y2="142" stroke="#dc2626" stroke-width="8" stroke-linecap="round" />
              <polygon points="24,142 46,131 46,153" fill="#dc2626" />
            </g>
          </svg>
        </div>
      </div>

    </div>

    
    <div class="controls">
      <button class="btn active" id="btnHighlight" aria-pressed="true">
        <span>✦</span>
        <span>Highlight Drag Forces</span>
      </button>
      <button class="btn" id="btnRipples" aria-pressed="false">
        <span>〰</span>
        <span>Toggle Water Ripples</span>
      </button>
    </div>
  </div>

  <script>
    const btnHighlight = document.getElementById('btnHighlight');
    const btnRipples = document.getElementById('btnRipples');
    const panelsWrapper = document.getElementById('panelsWrapper');
    const ripplesLayer = document.getElementById('ripplesLayer');

    let highlightActive = true;
    let ripplesActive = false;

    btnHighlight.addEventListener('click', () => {
      highlightActive = !highlightActive;
      btnHighlight.classList.toggle('active', highlightActive);
      btnHighlight.setAttribute('aria-pressed', highlightActive);
      panelsWrapper.classList.toggle('highlight-force', highlightActive);
    });

    btnRipples.addEventListener('click', () => {
      ripplesActive = !ripplesActive;
      btnRipples.classList.toggle('active', ripplesActive);
      btnRipples.setAttribute('aria-pressed', ripplesActive);
      ripplesLayer.style.opacity = ripplesActive ? '1' : '0';
    });
  </script>
</body>
</html>

science.ks3.y1.t5.s2

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