<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Uniform Circular Motion - Velocity & Speed</title>
  <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;
      width: 100%;
      min-height: 100%;
      padding: 10px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
    }

    .container {
      width: 100%;
      max-width: 620px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 10px;
    }

    .header-text {
      text-align: center;
      font-size: 13px;
      color: #475569;
      font-weight: 500;
    }

    .main-view {
      width: 100%;
      display: flex;
      flex-direction: row;
      align-items: center;
      justify-content: center;
      gap: 12px;
    }

    .track-container {
      width: 100%;
      max-width: 260px;
      aspect-ratio: 1 / 1;
      display: flex;
      align-items: center;
      justify-content: center;
      flex-shrink: 0;
    }

    svg.track-svg {
      width: 100%;
      height: 100%;
      display: block;
      overflow: visible;
      user-select: none;
    }

    .panel {
      flex: 1;
      min-width: 200px;
      display: flex;
      flex-direction: column;
      gap: 8px;
    }

    .stat-card {
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 8px;
      padding: 7px 10px;
      display: flex;
      justify-content: space-between;
      align-items: center;
      gap: 8px;
    }

    .stat-label {
      font-size: 12px;
      font-weight: 600;
      color: #64748b;
      white-space: nowrap;
    }

    .stat-val {
      font-size: 12px;
      font-weight: 700;
      text-align: right;
    }

    .val-const {
      color: #0284c7;
    }

    .val-dir {
      color: #0f172a;
      font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
    }

    .val-changing {
      color: #d97706;
    }

    .info-tip {
      font-size: 11px;
      line-height: 1.35;
      color: #475569;
      background: #f0f9ff;
      border-left: 3px solid #0284c7;
      padding: 6px 8px;
      border-radius: 0 6px 6px 0;
    }

    .controls {
      display: flex;
      flex-wrap: wrap;
      gap: 6px;
      width: 100%;
      justify-content: center;
      align-items: center;
    }

    .btn {
      background: #ffffff;
      border: 1px solid #cbd5e1;
      color: #334155;
      padding: 5px 10px;
      border-radius: 6px;
      font-size: 11px;
      font-weight: 600;
      cursor: pointer;
      user-select: none;
      transition: background 0.15s ease, border-color 0.15s ease, color 0.15s ease;
    }

    .btn:hover {
      background: #f1f5f9;
      border-color: #94a3b8;
    }

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

    .btn.primary:hover {
      background: #0369a1;
      border-color: #0369a1;
    }

    @media (max-width: 500px) {
      .main-view {
        flex-direction: column;
        gap: 8px;
      }
      .track-container {
        max-width: 220px;
      }
      .panel {
        width: 100%;
        min-width: unset;
      }
      .stat-card {
        padding: 6px 8px;
      }
      .btn {
        padding: 4px 8px;
        font-size: 10.5px;
      }
    }
  </style>
</head>
<body>

<div class="container">
  <div class="header-text">
    <strong>Uniform Circular Motion</strong>: Tangent Velocity Vector &amp; Speed
  </div>

  <div class="main-view">
    
    <div class="track-container">
      <svg class="track-svg" viewBox="0 0 300 300" aria-label="Circular track with moving car and tangent velocity vector">
        <defs>
          
          <marker id="arrow-active" viewBox="0 0 10 10" refX="7" refY="5" markerWidth="6" markerHeight="6" orient="auto">
            <path d="M 0 1.5 L 8 5 L 0 8.5 z" fill="#0284c7" />
          </marker>
          
          <marker id="arrow-ghost" viewBox="0 0 10 10" refX="7" refY="5" markerWidth="5" markerHeight="5" orient="auto">
            <path d="M 0 1.5 L 8 5 L 0 8.5 z" fill="#94a3b8" />
          </marker>
        </defs>

        
        <circle cx="150" cy="150" r="90" fill="none" stroke="#e2e8f0" stroke-width="32" />
        <circle cx="150" cy="150" r="106" fill="none" stroke="#cbd5e1" stroke-width="1.5" />
        <circle cx="150" cy="150" r="74" fill="none" stroke="#cbd5e1" stroke-width="1.5" />
        
        <circle cx="150" cy="150" r="90" fill="none" stroke="#cbd5e1" stroke-width="1.5" stroke-dasharray="5,5" />

        
        <circle cx="150" cy="150" r="3" fill="#64748b" />
        <text x="150" y="164" font-size="9" fill="#94a3b8" text-anchor="middle" font-weight="600">r = const</text>

        
        
        <g opacity="0.8">
          <line x1="150" y1="60" x2="198" y2="60" stroke="#94a3b8" stroke-width="1.5" stroke-dasharray="3,3" marker-end="url(#arrow-ghost)" />
          <circle cx="150" cy="60" r="2.5" fill="#94a3b8" />
          <text x="150" y="48" font-size="9.5" font-weight="700" fill="#64748b" text-anchor="middle">12:00 (East)</text>
        </g>

        
        <g opacity="0.8">
          <line x1="240" y1="150" x2="240" y2="198" stroke="#94a3b8" stroke-width="1.5" stroke-dasharray="3,3" marker-end="url(#arrow-ghost)" />
          <circle cx="240" cy="150" r="2.5" fill="#94a3b8" />
          <text x="248" y="153" font-size="9.5" font-weight="700" fill="#64748b" text-anchor="start">3:00 (South)</text>
        </g>

        
        <g opacity="0.8">
          <line x1="150" y1="240" x2="102" y2="240" stroke="#94a3b8" stroke-width="1.5" stroke-dasharray="3,3" marker-end="url(#arrow-ghost)" />
          <circle cx="150" cy="240" r="2.5" fill="#94a3b8" />
          <text x="150" y="258" font-size="9.5" font-weight="700" fill="#64748b" text-anchor="middle">6:00 (West)</text>
        </g>

        
        <g opacity="0.8">
          <line x1="60" y1="150" x2="60" y2="102" stroke="#94a3b8" stroke-width="1.5" stroke-dasharray="3,3" marker-end="url(#arrow-ghost)" />
          <circle cx="60" cy="150" r="2.5" fill="#94a3b8" />
          <text x="52" y="153" font-size="9.5" font-weight="700" fill="#64748b" text-anchor="end">9:00 (North)</text>
        </g>

        
        <g id="rotGroup" transform="rotate(0, 150, 150)">
          
          <line x1="150" y1="60" x2="204" y2="60" stroke="#0284c7" stroke-width="3" marker-end="url(#arrow-active)" />
          <text x="208" y="56" font-size="11" font-weight="800" fill="#0284c7">v</text>

          
          <line x1="150" y1="150" x2="150" y2="60" stroke="#0284c7" stroke-width="1" stroke-dasharray="2,2" opacity="0.4" />

          
          
          <rect x="139" y="49" width="6" height="3" rx="1" fill="#334155" />
          <rect x="155" y="49" width="6" height="3" rx="1" fill="#334155" />
          <rect x="139" y="68" width="6" height="3" rx="1" fill="#334155" />
          <rect x="155" y="68" width="6" height="3" rx="1" fill="#334155" />
          
          <rect x="136" y="52" width="28" height="16" rx="4" fill="#0f172a" stroke="#334155" stroke-width="1" />
          
          <rect x="142" y="55" width="13" height="10" rx="2" fill="#38bdf8" />
          
          <circle cx="163" cy="54.5" r="1.2" fill="#fef08a" />
          <circle cx="163" cy="65.5" r="1.2" fill="#fef08a" />
        </g>
      </svg>
    </div>

    
    <div class="panel">
      <div class="stat-card">
        <span class="stat-label">Speed (|v|)</span>
        <span class="stat-val val-const">10 m/s (Constant)</span>
      </div>
      <div class="stat-card">
        <span class="stat-label">Direction</span>
        <span class="stat-val val-dir" id="dirText">East &rarr;</span>
      </div>
      <div class="stat-card">
        <span class="stat-label">Velocity (v)</span>
        <span class="stat-val val-changing">Continuously Changing</span>
      </div>
      <div class="info-tip">
        Because direction turns continuously along the circle, <strong>velocity changes</strong> even while <strong>speed remains constant</strong>.
      </div>
    </div>
  </div>

  
  <div class="controls">
    <button class="btn primary" id="playBtn" onclick="togglePlay()">&#10074;&#10074; Pause</button>
    <button class="btn" onclick="jumpTo(0)">12 o'clock (East)</button>
    <button class="btn" onclick="jumpTo(90)">3 o'clock (South)</button>
    <button class="btn" onclick="jumpTo(180)">6 o'clock (West)</button>
    <button class="btn" onclick="jumpTo(270)">9 o'clock (North)</button>
  </div>
</div>

<script>
  let angle = 0;
  let isPlaying = true;
  let lastTime = null;
  const speedDegPerSec = 45; // 8 seconds per full revolution

  const rotGroup = document.getElementById('rotGroup');
  const dirText = document.getElementById('dirText');
  const playBtn = document.getElementById('playBtn');

  function getDirectionName(deg) {
    const d = (deg % 360 + 360) % 360;
    if (d >= 337.5 || d < 22.5) return 'East \u2192';
    if (d >= 22.5 && d < 67.5) return 'South-East \u2198';
    if (d >= 67.5 && d < 112.5) return 'South \u2193';
    if (d >= 112.5 && d < 157.5) return 'South-West \u2199';
    if (d >= 157.5 && d < 202.5) return 'West \u2190';
    if (d >= 202.5 && d < 247.5) return 'North-West \u2196';
    if (d >= 247.5 && d < 292.5) return 'North \u2191';
    return 'North-East \u2197';
  }

  function updateView() {
    rotGroup.setAttribute('transform', `rotate(${angle}, 150, 150)`);
    dirText.textContent = getDirectionName(angle);
  }

  function loop(time) {
    if (!lastTime) lastTime = time;
    const dt = (time - lastTime) / 1000;
    lastTime = time;

    if (isPlaying) {
      angle = (angle + speedDegPerSec * dt) % 360;
      updateView();
    }
    requestAnimationFrame(loop);
  }

  function togglePlay() {
    isPlaying = !isPlaying;
    playBtn.innerHTML = isPlaying ? '&#10074;&#10074; Pause' : '&#9654; Play';
  }

  function jumpTo(deg) {
    angle = deg;
    updateView();
  }

  updateView();
  requestAnimationFrame(loop);
</script>

</body>
</html>

Uniform Circular Motion: Moving in a Circle at Constant Speed

<!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;
      padding: 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
      gap: 12px;
    }

    .cards-row {
      display: flex;
      flex-direction: row;
      gap: 12px;
      width: 100%;
      max-width: 640px;
      flex: 1;
    }

    .concept-card {
      flex: 1;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      border-radius: 12px;
      padding: 14px 10px;
      background: #ffffff;
      transition: border-color 0.2s ease;
    }

    .scalar-card {
      border: 2px solid #f59e0b;
      background: #fffdfa;
    }

    .vector-card {
      border: 2px solid #0284c7;
      background: #f8fcff;
    }

    .card-header {
      text-align: center;
      margin-bottom: 6px;
    }

    .card-title {
      font-size: 17px;
      font-weight: 800;
      letter-spacing: -0.01em;
    }

    .scalar-title { color: #b45309; }
    .vector-title { color: #0369a1; }

    .card-type {
      font-size: 12px;
      font-weight: 600;
      text-transform: uppercase;
      letter-spacing: 0.05em;
      opacity: 0.8;
    }

    .vis-box {
      width: 100%;
      height: 130px;
      display: flex;
      align-items: center;
      justify-content: center;
      position: relative;
    }

    .speedo-svg {
      width: 130px;
      height: 105px;
    }

    .car-stage {
      width: 130px;
      height: 130px;
      position: relative;
      display: flex;
      align-items: center;
      justify-content: center;
      transition: transform 0.35s cubic-bezier(0.4, 0, 0.2, 1);
    }

    .labels-box {
      width: 100%;
      display: flex;
      flex-direction: column;
      gap: 6px;
      margin-top: 6px;
    }

    .badge {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      padding: 6px 10px;
      border-radius: 8px;
      font-size: 13px;
      font-weight: 700;
      text-align: center;
    }

    .badge-scalar {
      background: #fef3c7;
      color: #92400e;
      border: 1px solid #fde68a;
    }

    .badge-vector-mag {
      background: #e0f2fe;
      color: #0369a1;
      border: 1px solid #bae6fd;
    }

    .badge-vector-dir {
      background: #0284c7;
      color: #ffffff;
      border: 1px solid #0284c7;
      transition: background-color 0.2s;
    }

    .controls-bar {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      width: 100%;
      max-width: 640px;
      background: #f1f5f9;
      padding: 6px 10px;
      border-radius: 10px;
    }

    .ctrl-label {
      font-size: 12px;
      font-weight: 700;
      color: #475569;
      text-transform: uppercase;
    }

    .dir-btn {
      flex: 1;
      max-width: 70px;
      padding: 6px 0;
      border: 1px solid #cbd5e1;
      border-radius: 6px;
      background: #ffffff;
      font-size: 13px;
      font-weight: 700;
      color: #334155;
      cursor: pointer;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 4px;
      transition: all 0.15s ease;
      user-select: none;
    }

    .dir-btn.active {
      background: #0284c7;
      color: #ffffff;
      border-color: #0284c7;
      box-shadow: 0 1px 3px rgba(2, 132, 199, 0.3);
    }

    @media (max-width: 480px) {
      body { padding: 8px; gap: 8px; }
      .cards-row { gap: 8px; }
      .concept-card { padding: 10px 6px; }
      .card-title { font-size: 15px; }
      .card-type { font-size: 11px; }
      .vis-box { height: 110px; }
      .speedo-svg { width: 110px; height: 90px; }
      .car-stage { width: 110px; height: 110px; }
      .badge { font-size: 11.5px; padding: 5px 6px; }
      .dir-btn { font-size: 12px; padding: 5px 0; }
    }
  </style>
</head>
<body>

  <div class="cards-row">
    
    <div class="concept-card scalar-card">
      <div class="card-header">
        <div class="card-title scalar-title">Speed</div>
        <div class="card-type">Scalar</div>
      </div>

      <div class="vis-box">
        <svg class="speedo-svg" viewBox="0 0 120 95">
          
          <path d="M 20 80 A 42 42 0 1 1 100 80" fill="none" stroke="#fed7aa" stroke-width="10" stroke-linecap="round" />
          
          <path d="M 20 80 A 42 42 0 0 1 60 18" fill="none" stroke="#f59e0b" stroke-width="10" stroke-linecap="round" />
          
          <line x1="20" y1="80" x2="27" y2="75" stroke="#b45309" stroke-width="2" />
          <line x1="60" y1="18" x2="60" y2="26" stroke="#b45309" stroke-width="2.5" />
          <line x1="100" y1="80" x2="93" y2="75" stroke="#b45309" stroke-width="2" />
          
          <text x="60" y="58" text-anchor="middle" font-size="16" font-weight="800" fill="#78350f">20</text>
          <text x="60" y="72" text-anchor="middle" font-size="10" font-weight="700" fill="#b45309">m/s</text>
          
          <circle cx="60" cy="80" r="5" fill="#78350f" />
          <line x1="60" y1="80" x2="60" y2="28" stroke="#78350f" stroke-width="3" stroke-linecap="round" />
        </svg>
      </div>

      <div class="labels-box">
        <div class="badge badge-scalar">Magnitude only</div>
      </div>
    </div>

    
    <div class="concept-card vector-card">
      <div class="card-header">
        <div class="card-title vector-title">Velocity</div>
        <div class="card-type">Vector</div>
      </div>

      <div class="vis-box">
        <div class="car-stage" id="carStage">
          <svg viewBox="0 0 100 100" width="100" height="100">
            
            <defs>
              <marker id="arrowhead" markerWidth="6" markerHeight="6" refX="4" refY="3" orient="auto">
                <polygon points="0 0, 6 3, 0 6" fill="#0284c7" />
              </marker>
            </defs>
            <line x1="50" y1="46" x2="50" y2="10" stroke="#0284c7" stroke-width="4" stroke-linecap="round" marker-end="url(#arrowhead)" />
            
            
            <rect x="36" y="46" width="28" height="42" rx="6" fill="#0284c7" />
            
            <path d="M 39 58 L 61 58 L 58 50 L 42 50 Z" fill="#bae6fd" />
            
            <rect x="40" y="76" width="20" height="4" rx="1.5" fill="#bae6fd" />
            
            <rect x="32" y="50" width="4" height="9" rx="2" fill="#1e2945" />
            <rect x="64" y="50" width="4" height="9" rx="2" fill="#1e2945" />
            <rect x="32" y="74" width="4" height="9" rx="2" fill="#1e2945" />
            <rect x="64" y="74" width="4" height="9" rx="2" fill="#1e2945" />
            
            <circle cx="40" cy="47" r="2" fill="#fef08a" />
            <circle cx="60" cy="47" r="2" fill="#fef08a" />
          </svg>
        </div>
      </div>

      <div class="labels-box">
        <div class="badge badge-vector-mag">Magnitude: 20 m/s</div>
        <div class="badge badge-vector-dir" id="dirBadge">Direction: North</div>
      </div>
    </div>
  </div>

  
  <div class="controls-bar">
    <span class="ctrl-label">Turn Car:</span>
    <button class="dir-btn active" data-dir="North" data-rot="0">↑ N</button>
    <button class="dir-btn" data-dir="East" data-rot="90">→ E</button>
    <button class="dir-btn" data-dir="South" data-rot="180">↓ S</button>
    <button class="dir-btn" data-dir="West" data-rot="270">← W</button>
  </div>

  <script>
    const carStage = document.getElementById('carStage');
    const dirBadge = document.getElementById('dirBadge');
    const buttons = document.querySelectorAll('.dir-btn');

    buttons.forEach(btn => {
      btn.addEventListener('click', () => {
        buttons.forEach(b => b.classList.remove('active'));
        btn.classList.add('active');

        const deg = btn.getAttribute('data-rot');
        const dir = btn.getAttribute('data-dir');

        carStage.style.transform = `rotate(${deg}deg)`;
        dirBadge.textContent = `Direction: ${dir}`;
      });
    });
  </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="1:1">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      background: #0f172a;
      color: #f8fafc;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      min-height: 100%;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      padding: 12px;
      user-select: none;
    }

    .diagram-root {
      width: 100%;
      max-width: 520px;
      display: flex;
      flex-direction: column;
      gap: 14px;
    }

    /* Header */
    .header {
      text-align: center;
    }
    .badge-title {
      display: inline-block;
      font-size: 11px;
      font-weight: 700;
      letter-spacing: 0.08em;
      text-transform: uppercase;
      color: #94a3b8;
      background: rgba(148, 163, 184, 0.12);
      padding: 3px 10px;
      border-radius: 999px;
      margin-bottom: 4px;
    }
    .main-title {
      font-size: 16px;
      font-weight: 600;
      color: #e2e8f0;
    }

    /* Equation Section */
    .formula-stage {
      position: relative;
      background: #1e293b;
      border-radius: 16px;
      padding: 24px 16px 20px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      box-shadow: 0 4px 20px rgba(0,0,0,0.25);
    }

    .delta-badge {
      display: flex;
      align-items: center;
      gap: 6px;
      font-size: 12px;
      font-weight: 600;
      color: #38bdf8;
      background: rgba(56, 189, 248, 0.12);
      border: 1px solid rgba(56, 189, 248, 0.3);
      padding: 4px 12px;
      border-radius: 20px;
      margin-bottom: 12px;
      transition: all 0.25s ease;
    }

    .bracket-svg {
      width: 130px;
      height: 10px;
      margin-bottom: 6px;
    }

    .equation-row {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 10px;
      font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
      font-size: 32px;
      font-weight: 700;
      line-height: 1;
    }

    .var-btn {
      background: none;
      border: none;
      font-family: inherit;
      font-size: inherit;
      font-weight: inherit;
      cursor: pointer;
      padding: 4px 8px;
      border-radius: 8px;
      transition: background 0.2s ease, transform 0.15s ease, box-shadow 0.2s ease;
      color: inherit;
      position: relative;
    }
    .var-btn:active {
      transform: scale(0.95);
    }

    .fraction-wrap {
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 6px;
    }

    .frac-top {
      display: flex;
      align-items: center;
      gap: 4px;
    }

    .frac-bar {
      width: 100%;
      min-width: 140px;
      height: 3px;
      background: #64748b;
      border-radius: 2px;
      transition: background 0.2s ease;
    }

    .operator {
      color: #94a3b8;
      font-size: 26px;
      font-weight: 400;
    }

    /* Color classes */
    .c-a { color: #c084fc; }
    .c-v { color: #34d399; }
    .c-u { color: #38bdf8; }
    .c-t { color: #fbbf24; }

    .bg-a-active { background: rgba(192, 132, 252, 0.2); box-shadow: 0 0 0 2px #a855f7; }
    .bg-v-active { background: rgba(52, 211, 153, 0.2); box-shadow: 0 0 0 2px #10b981; }
    .bg-u-active { background: rgba(56, 189, 248, 0.2); box-shadow: 0 0 0 2px #0ea5e9; }
    .bg-t-active { background: rgba(251, 191, 36, 0.2); box-shadow: 0 0 0 2px #f59e0b; }

    /* Variable Grid */
    .vars-grid {
      display: grid;
      grid-template-columns: repeat(2, 1fr);
      gap: 8px;
    }

    .var-card {
      background: #1e293b;
      border-radius: 12px;
      padding: 10px 12px;
      border: 1.5px solid transparent;
      cursor: pointer;
      display: flex;
      flex-direction: column;
      gap: 3px;
      transition: border-color 0.2s ease, background 0.2s ease;
    }

    .card-a { border-color: rgba(168, 85, 247, 0.25); }
    .card-v { border-color: rgba(16, 185, 129, 0.25); }
    .card-u { border-color: rgba(14, 165, 233, 0.25); }
    .card-t { border-color: rgba(245, 158, 11, 0.25); }

    .card-a.active { border-color: #a855f7; background: rgba(168, 85, 247, 0.12); }
    .card-v.active { border-color: #10b981; background: rgba(16, 185, 129, 0.12); }
    .card-u.active { border-color: #0ea5e9; background: rgba(14, 165, 233, 0.12); }
    .card-t.active { border-color: #f59e0b; background: rgba(245, 158, 11, 0.12); }

    .card-header {
      display: flex;
      align-items: center;
      justify-content: space-between;
    }

    .card-sym {
      font-family: ui-monospace, monospace;
      font-weight: 700;
      font-size: 16px;
    }

    .card-unit {
      font-size: 11px;
      font-weight: 600;
      padding: 2px 7px;
      border-radius: 6px;
      background: rgba(255, 255, 255, 0.07);
      color: #cbd5e1;
      font-family: ui-monospace, monospace;
    }

    .card-name {
      font-size: 12px;
      font-weight: 600;
      color: #f1f5f9;
    }

    .card-desc {
      font-size: 11px;
      color: #94a3b8;
      line-height: 1.25;
    }

    /* Unit Derivation Flow */
    .unit-flow {
      background: #1e293b;
      border-radius: 12px;
      padding: 10px 14px;
      display: flex;
      align-items: center;
      justify-content: space-between;
      gap: 6px;
      font-family: ui-monospace, monospace;
      font-size: 12px;
      color: #94a3b8;
    }

    .flow-tag {
      display: flex;
      align-items: center;
      gap: 5px;
      font-weight: 600;
    }

    .tag-val {
      padding: 3px 8px;
      border-radius: 6px;
      font-weight: 700;
    }

    .u-vel { background: rgba(16, 185, 129, 0.15); color: #34d399; }
    .u-tim { background: rgba(245, 158, 11, 0.15); color: #fbbf24; }
    .u-acc { background: rgba(168, 85, 247, 0.2); color: #c084fc; border: 1px solid rgba(168, 85, 247, 0.4); }

    .arrow-sym {
      color: #64748b;
      font-size: 13px;
    }
  </style>
</head>
<body>

  <div class="diagram-root">
    
    
    <div class="header">
      <div class="badge-title">Formula Breakdown</div>
      <div class="main-title">Acceleration: Rate of Change of Velocity</div>
    </div>

    
    <div class="formula-stage">
      
      
      <div class="delta-badge" id="deltaBadge">
        <span>Change in Velocity</span>
        <span style="opacity:0.75;">(Δv = v − u)</span>
      </div>

      <svg class="bracket-svg" viewBox="0 0 130 10" fill="none">
        <path d="M 2 8 Q 2 2 12 2 L 55 2 Q 65 2 65 0 Q 65 2 75 2 L 118 2 Q 128 2 128 8" stroke="#38bdf8" stroke-width="1.75" stroke-linecap="round" fill="none" />
      </svg>

      
      <div class="equation-row">
        <button class="var-btn c-a" id="btn-a" onclick="selectVar('a')">a</button>
        <span class="operator">=</span>
        <div class="fraction-wrap">
          <div class="frac-top">
            <span class="operator">(</span>
            <button class="var-btn c-v" id="btn-v" onclick="selectVar('v')">v</button>
            <span class="operator">−</span>
            <button class="var-btn c-u" id="btn-u" onclick="selectVar('u')">u</button>
            <span class="operator">)</span>
          </div>
          <div class="frac-bar"></div>
          <button class="var-btn c-t" id="btn-t" onclick="selectVar('t')">t</button>
        </div>
      </div>

    </div>

    
    <div class="vars-grid">
      
      
      <div class="var-card card-a active" id="card-a" onclick="selectVar('a')">
        <div class="card-header">
          <span class="card-sym c-a">a</span>
          <span class="card-unit">m/s²</span>
        </div>
        <div class="card-name">Acceleration</div>
        <div class="card-desc">Rate of velocity change</div>
      </div>

      
      <div class="var-card card-v" id="card-v" onclick="selectVar('v')">
        <div class="card-header">
          <span class="card-sym c-v">v</span>
          <span class="card-unit">m/s</span>
        </div>
        <div class="card-name">Final Velocity</div>
        <div class="card-desc">Velocity at the end</div>
      </div>

      
      <div class="var-card card-u" id="card-u" onclick="selectVar('u')">
        <div class="card-header">
          <span class="card-sym c-u">u</span>
          <span class="card-unit">m/s</span>
        </div>
        <div class="card-name">Initial Velocity</div>
        <div class="card-desc">Velocity at the start</div>
      </div>

      
      <div class="var-card card-t" id="card-t" onclick="selectVar('t')">
        <div class="card-header">
          <span class="card-sym c-t">t</span>
          <span class="card-unit">s</span>
        </div>
        <div class="card-name">Time Taken</div>
        <div class="card-desc">Duration of change</div>
      </div>

    </div>

    
    <div class="unit-flow">
      <span class="tag-val u-vel">m/s</span>
      <span class="arrow-sym">÷</span>
      <span class="tag-val u-tim">s</span>
      <span class="arrow-sym">=</span>
      <span style="font-size:11px; color:#cbd5e1;">(m/s)/s</span>
      <span class="arrow-sym">→</span>
      <span class="tag-val u-acc">m/s²</span>
    </div>

  </div>

  <script>
    const vars = ['a', 'v', 'u', 't'];

    function selectVar(activeKey) {
      vars.forEach(k => {
        const btn = document.getElementById(`btn-${k}`);
        const card = document.getElementById(`card-${k}`);
        
        if (k === activeKey) {
          btn.classList.add(`bg-${k}-active`);
          card.classList.add('active');
        } else {
          btn.classList.remove(`bg-${k}-active`);
          card.classList.remove('active');
        }
      });

      const deltaBadge = document.getElementById('deltaBadge');
      if (activeKey === 'v' || activeKey === 'u') {
        deltaBadge.style.background = 'rgba(56, 189, 248, 0.25)';
        deltaBadge.style.borderColor = '#38bdf8';
      } else {
        deltaBadge.style.background = 'rgba(56, 189, 248, 0.12)';
        deltaBadge.style.borderColor = 'rgba(56, 189, 248, 0.3)';
      }
    }

    // Initialize with 'a' selected
    selectVar('a');
  </script>
</body>
</html>

Defining Acceleration as the Rate of Change of Velocity

<!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">
  <link rel="stylesheet" href="{{VENDOR_CDN}}/katex.min.css">
  <script src="{{VENDOR_CDN}}/katex.min.js"></script>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }
    body {
      width: 100%;
      min-height: 100%;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #ffffff;
      color: #0f172a;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      padding: 14px 12px;
      user-select: none;
      gap: 12px;
    }

    /* Stepper Navigation */
    .controls {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      width: 100%;
      max-width: 480px;
    }
    .step-btn {
      flex: 1;
      padding: 8px 4px;
      font-size: 12px;
      font-weight: 600;
      border: 1.5px solid #cbd5e1;
      background: #f8fafc;
      color: #334155;
      border-radius: 8px;
      cursor: pointer;
      display: flex;
      align-items: center;
      justify-content: center;
      text-align: center;
      transition: background-color 0.4s ease, border-color 0.4s ease, color 0.4s ease, box-shadow 0.4s ease;
      white-space: nowrap;
    }
    .step-btn:hover {
      background: #f1f5f9;
      border-color: #94a3b8;
    }
    .step-btn.active {
      background: #0284c7;
      color: #ffffff;
      border-color: #0284c7;
      box-shadow: 0 2px 6px rgba(2, 132, 199, 0.25);
    }
    .play-btn {
      width: 36px;
      height: 34px;
      padding: 0;
      flex: 0 0 36px;
      border: 1.5px solid #cbd5e1;
      background: #f8fafc;
      color: #1e293b;
      border-radius: 8px;
      cursor: pointer;
      font-size: 14px;
      display: flex;
      align-items: center;
      justify-content: center;
      transition: background-color 0.3s ease, border-color 0.3s ease;
    }
    .play-btn:hover {
      background: #e2e8f0;
    }

    /* Calculation Board */
    .calc-board {
      width: 100%;
      max-width: 480px;
      display: flex;
      flex-direction: column;
      gap: 10px;
      margin: 2px 0;
    }

    .calc-row {
      display: flex;
      align-items: center;
      justify-content: space-between;
      flex-wrap: wrap;
      gap: 8px;
      padding: 10px 14px;
      border-radius: 10px;
      border: 1.5px solid #cbd5e1;
      background: #f8fafc;
      opacity: 0.85;
      transition: opacity 0.5s ease, border-color 0.5s ease, background-color 0.5s ease, box-shadow 0.5s ease;
    }

    .calc-row.active {
      opacity: 1;
      border-color: #0284c7;
      background: #f0f9ff;
      box-shadow: 0 2px 8px rgba(2, 132, 199, 0.15);
    }

    .calc-row.past {
      opacity: 0.95;
      border-color: #94a3b8;
      background: #ffffff;
    }

    .row-label {
      display: flex;
      align-items: center;
      gap: 8px;
      font-size: 13px;
      font-weight: 700;
      color: #334155;
      min-width: 85px;
      flex-shrink: 0;
    }
    .calc-row.active .row-label {
      color: #0369a1;
    }
    .step-num {
      width: 22px;
      height: 22px;
      border-radius: 50%;
      background: #e2e8f0;
      color: #1e293b;
      font-size: 12px;
      display: flex;
      align-items: center;
      justify-content: center;
      font-weight: 700;
      transition: background-color 0.5s ease, color 0.5s ease;
    }
    .calc-row.active .step-num {
      background: #0284c7;
      color: #ffffff;
    }
    .calc-row.past .step-num {
      background: #cbd5e1;
      color: #0f172a;
    }

    .row-math {
      font-size: 15px;
      font-weight: 600;
      color: #0f172a;
      display: flex;
      align-items: center;
      flex-wrap: wrap;
      gap: 8px;
    }

    /* Badges & Tags */
    .chip {
      font-size: 11px;
      font-weight: 700;
      padding: 2px 7px;
      border-radius: 4px;
      background: #e0f2fe;
      color: #0369a1;
      flex-shrink: 0;
    }

    .unit-badge {
      display: inline-flex;
      align-items: center;
      background: #0284c7;
      color: #ffffff;
      padding: 3px 8px;
      border-radius: 6px;
      font-weight: 700;
      font-size: 13px;
      letter-spacing: 0.5px;
      box-shadow: 0 2px 6px rgba(2, 132, 199, 0.35);
    }

    /* Subtext Info Footer */
    .info-bar {
      font-size: 12px;
      color: #334155;
      font-weight: 500;
      display: flex;
      align-items: center;
      justify-content: center;
      flex-wrap: wrap;
      gap: 6px;
      text-align: center;
      max-width: 480px;
      width: 100%;
    }

    /* Responsive Mobile Layout Adjustments */
    @media (max-width: 420px) {
      .controls {
        gap: 4px;
      }
      .step-btn {
        font-size: 11px;
        padding: 6px 2px;
      }
      .calc-row {
        flex-direction: column;
        align-items: flex-start;
        padding: 8px 12px;
        gap: 4px;
      }
      .row-math {
        width: 100%;
        font-size: 14px;
      }
      .info-bar {
        font-size: 11px;
      }
    }
  </style>
</head>
<body>

  
  <div class="controls">
    <button class="step-btn active" data-step="0">1. Values</button>
    <button class="step-btn" data-step="1">2. Formula</button>
    <button class="step-btn" data-step="2">3. Substitute</button>
    <button class="step-btn" data-step="3">4. Solve</button>
    <button class="play-btn" id="playBtn" title="Play/Pause" aria-label="Play/Pause">⏸</button>
  </div>

  
  <div class="calc-board">
    
    <div class="calc-row active" id="row-0">
      <div class="row-label">
        <span class="step-num">1</span>
        <span>Identify</span>
      </div>
      <div class="row-math" id="math-1"></div>
    </div>

    
    <div class="calc-row" id="row-1">
      <div class="row-label">
        <span class="step-num">2</span>
        <span>Formula</span>
      </div>
      <div class="row-math" id="math-2"></div>
    </div>

    
    <div class="calc-row" id="row-2">
      <div class="row-label">
        <span class="step-num">3</span>
        <span>Substitute</span>
      </div>
      <div class="row-math" id="math-3"></div>
    </div>

    
    <div class="calc-row" id="row-3">
      <div class="row-label">
        <span class="step-num">4</span>
        <span>Answer</span>
      </div>
      <div class="row-math" id="math-4"></div>
    </div>
  </div>

  <div class="info-bar">
    <span class="chip">Tip</span>
    <span>"From rest" means initial velocity <span id="math-tip"></span></span>
  </div>

  <script>
    // KaTeX Expressions
    function renderFormulas() {
      if (typeof katex !== 'undefined') {
        katex.render("u = 0\\,\\text{m/s},\\; v = 12\\,\\text{m/s},\\; t = 4.0\\,\\text{s}", document.getElementById('math-1'));
        katex.render("a = \\frac{v - u}{t}", document.getElementById('math-2'));
        katex.render("a = \\frac{12 - 0}{4.0}", document.getElementById('math-3'));
        katex.render("a = 3.0", document.getElementById('math-4'));
        
        // Append unit badge with blue highlight
        const badge = document.createElement('span');
        badge.className = 'unit-badge';
        badge.textContent = 'm/s²';
        document.getElementById('math-4').appendChild(badge);

        katex.render("u = 0\\,\\text{m/s}", document.getElementById('math-tip'));
      } else {
        // Fallback if KaTeX fails to load
        document.getElementById('math-1').textContent = "u = 0 m/s, v = 12 m/s, t = 4.0 s";
        document.getElementById('math-2').textContent = "a = (v - u) / t";
        document.getElementById('math-3').textContent = "a = (12 - 0) / 4.0";
        document.getElementById('math-4').innerHTML = 'a = 3.0 <span class="unit-badge">m/s²</span>';
        document.getElementById('math-tip').textContent = "u = 0 m/s";
      }
    }
    renderFormulas();

    // Stepper State
    let currentStep = 0;
    const totalSteps = 4;
    let isPlaying = true;
    let timer = null;

    const stepBtns = document.querySelectorAll('.step-btn');
    const playBtn = document.getElementById('playBtn');

    function updateView() {
      stepBtns.forEach((btn, idx) => {
        btn.classList.toggle('active', idx === currentStep);
      });

      for (let i = 0; i < totalSteps; i++) {
        const row = document.getElementById(`row-${i}`);
        row.classList.remove('active', 'past');
        if (i === currentStep) {
          row.classList.add('active');
        } else if (i < currentStep) {
          row.classList.add('past');
        }
      }
    }

    function setStep(idx) {
      currentStep = idx;
      updateView();
    }

    function nextStep() {
      currentStep = (currentStep + 1) % totalSteps;
      updateView();
    }

    function startAutoPlay() {
      if (timer) clearInterval(timer);
      timer = setInterval(nextStep, 4500);
      isPlaying = true;
      playBtn.textContent = '⏸';
    }

    function pauseAutoPlay() {
      if (timer) clearInterval(timer);
      timer = null;
      isPlaying = false;
      playBtn.textContent = '▶';
    }

    stepBtns.forEach((btn) => {
      btn.addEventListener('click', () => {
        pauseAutoPlay();
        setStep(parseInt(btn.getAttribute('data-step'), 10));
      });
    });

    playBtn.addEventListener('click', () => {
      if (isPlaying) {
        pauseAutoPlay();
      } else {
        nextStep();
        startAutoPlay();
      }
    });

    // Start paced loop
    startAutoPlay();
  </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">
  <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: #1e2945;
      padding: 8px 12px 12px 12px;
      display: flex;
      flex-direction: column;
      gap: 10px;
      user-select: none;
    }

    .controls {
      display: flex;
      justify-content: space-between;
      align-items: center;
      gap: 8px;
    }

    .btn {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      color: #1e2945;
      padding: 6px 14px;
      border-radius: 8px;
      font-size: 13px;
      font-weight: 600;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 6px;
      transition: background 0.2s, border-color 0.2s;
    }
    .btn:active { background: #e2e8f0; }

    .grid-panels {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 12px;
    }
    @media (max-width: 520px) {
      .grid-panels {
        grid-template-columns: 1fr;
      }
    }

    .panel-box {
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 10px;
      padding: 10px 12px;
      display: flex;
      flex-direction: column;
      gap: 8px;
    }

    .panel-header {
      display: flex;
      justify-content: space-between;
      align-items: baseline;
      font-size: 14px;
      font-weight: 700;
    }
    .text-pos { color: #0284c7; }
    .text-neg { color: #e11d48; }

    .badge {
      font-size: 11px;
      font-weight: 600;
      padding: 2px 8px;
      border-radius: 999px;
      letter-spacing: 0.2px;
    }
    .badge-pos { background: #e0f2fe; color: #0369a1; }
    .badge-neg { background: #ffe4e6; color: #be123c; }

    .track-svg {
      width: 100%;
      height: 110px;
      overflow: visible;
    }

    .summary-bar {
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 8px;
      padding: 8px 12px;
      font-size: 13px;
      font-weight: 600;
      text-align: center;
      color: #334155;
    }
    .math-hl {
      color: #e11d48;
      font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
    }
  </style>
</head>
<body>

  <div class="controls">
    <div style="font-size: 14px; font-weight: 700; color: #0f172a;">Direction of Vectors</div>
    <button class="btn" id="playBtn">▶ Replay Motion</button>
  </div>

  <div class="grid-panels">
    
    <div class="panel-box">
      <div class="panel-header">
        <span class="text-pos">Speeding Up (+a)</span>
        <span class="badge badge-pos">Same Direction</span>
      </div>

      <svg class="track-svg" viewBox="0 0 300 110">
        
        <line x1="10" y1="92" x2="290" y2="92" stroke="#94a3b8" stroke-width="2" stroke-dasharray="6,6" />
        <line x1="10" y1="96" x2="290" y2="96" stroke="#64748b" stroke-width="2" />

        
        <g transform="translate(10, 18)">
          <line x1="0" y1="0" x2="160" y2="0" stroke="#10b981" stroke-width="4" stroke-linecap="round" />
          <polygon points="160,-5 172,0 160,5" fill="#10b981" />
          <text x="5" y="-6" fill="#047857" font-size="11" font-weight="700">Velocity (v) →</text>
        </g>

        
        <g transform="translate(10, 42)">
          <line x1="0" y1="0" x2="110" y2="0" stroke="#0284c7" stroke-width="4" stroke-linecap="round" />
          <polygon points="110,-5 122,0 110,5" fill="#0284c7" />
          <text x="5" y="-6" fill="#0369a1" font-size="11" font-weight="700">Acceleration (+a) →</text>
        </g>

        
        <text x="15" y="106" fill="#64748b" font-size="10" font-weight="600">u = 5 m/s</text>
        <text x="235" y="106" fill="#64748b" font-size="10" font-weight="600">v = 15 m/s</text>

        
        <g id="carPos" transform="translate(15, 68)">
          
          <rect x="0" y="8" width="46" height="14" rx="4" fill="#38bdf8" />
          <path d="M 8 8 L 16 0 L 32 0 L 38 8 Z" fill="#0284c7" />
          <rect x="18" y="2" width="12" height="6" fill="#e0f2fe" opacity="0.9" />
          
          <circle cx="11" cy="22" r="4.5" fill="#1e293b" />
          <circle cx="11" cy="22" r="2" fill="#94a3b8" />
          <circle cx="35" cy="22" r="4.5" fill="#1e293b" />
          <circle cx="35" cy="22" r="2" fill="#94a3b8" />
        </g>
      </svg>
    </div>

    
    <div class="panel-box">
      <div class="panel-header">
        <span class="text-neg">Slowing Down (-a)</span>
        <span class="badge badge-neg">Opposite Direction</span>
      </div>

      <svg class="track-svg" viewBox="0 0 300 110">
        
        <line x1="10" y1="92" x2="290" y2="92" stroke="#94a3b8" stroke-width="2" stroke-dasharray="6,6" />
        <line x1="10" y1="96" x2="290" y2="96" stroke="#64748b" stroke-width="2" />

        
        <g transform="translate(10, 18)">
          <line x1="0" y1="0" x2="160" y2="0" stroke="#10b981" stroke-width="4" stroke-linecap="round" />
          <polygon points="160,-5 172,0 160,5" fill="#10b981" />
          <text x="5" y="-6" fill="#047857" font-size="11" font-weight="700">Velocity (v) →</text>
        </g>

        
        <g transform="translate(180, 42)">
          <line x1="0" y1="0" x2="-110" y2="0" stroke="#e11d48" stroke-width="4" stroke-linecap="round" />
          <polygon points="-110,-5 -122,0 -110,5" fill="#e11d48" />
          <text x="-115" y="-6" fill="#be123c" font-size="11" font-weight="700">← Acceleration (-a)</text>
        </g>

        
        <text x="15" y="106" fill="#64748b" font-size="10" font-weight="600">u = 20 m/s</text>
        <text x="240" y="106" fill="#64748b" font-size="10" font-weight="600">v = 0 m/s</text>

        
        <g id="carNeg" transform="translate(15, 68)">
          
          <rect x="0" y="8" width="46" height="14" rx="4" fill="#fb7185" />
          <path d="M 8 8 L 16 0 L 32 0 L 38 8 Z" fill="#e11d48" />
          <rect x="18" y="2" width="12" height="6" fill="#ffe4e6" opacity="0.9" />
          
          <circle cx="11" cy="22" r="4.5" fill="#1e293b" />
          <circle cx="11" cy="22" r="2" fill="#94a3b8" />
          <circle cx="35" cy="22" r="4.5" fill="#1e293b" />
          <circle cx="35" cy="22" r="2" fill="#94a3b8" />
        </g>
      </svg>
    </div>
  </div>

  <div class="summary-bar">
    Negative acceleration <span class="math-hl">(-4 m/s²)</span> = Deceleration of <span class="math-hl">4 m/s²</span>
  </div>

  <script>
    const carPos = document.getElementById('carPos');
    const carNeg = document.getElementById('carNeg');
    const playBtn = document.getElementById('playBtn');

    let animStartTime = null;
    const duration = 2400; // 2.4s

    function animate(timestamp) {
      if (!animStartTime) animStartTime = timestamp;
      const elapsed = timestamp - animStartTime;
      const progress = Math.min(elapsed / duration, 1);

      // Positive acceleration: x = u*t + 0.5*a*t^2 (starts slow, speeds up -> easeInQuad)
      const distPos = 15 + (225 * Math.pow(progress, 1.8));

      // Negative acceleration: deceleration (starts fast, slows down to stop -> easeOutQuad)
      const distNeg = 15 + (225 * (1 - Math.pow(1 - progress, 1.8)));

      carPos.setAttribute('transform', `translate(${distPos}, 68)`);
      carNeg.setAttribute('transform', `translate(${distNeg}, 68)`);

      if (progress < 1) {
        requestAnimationFrame(animate);
      } else {
        setTimeout(() => {
          resetCars();
        }, 1200);
      }
    }

    function resetCars() {
      carPos.setAttribute('transform', 'translate(15, 68)');
      carNeg.setAttribute('transform', 'translate(15, 68)');
      animStartTime = null;
    }

    function triggerAnimation() {
      resetCars();
      requestAnimationFrame((t) => {
        animStartTime = t;
        requestAnimationFrame(animate);
      });
    }

    playBtn.addEventListener('click', triggerAnimation);

    // Initial play after slight load delay
    setTimeout(() => {
      triggerAnimation();
    }, 600);
  </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">
  <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: #ffffff;
      padding: 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
    }
    .stepper-nav {
      display: flex;
      gap: 6px;
      width: 100%;
      max-width: 480px;
      justify-content: center;
      margin-bottom: 8px;
    }
    .step-btn {
      flex: 1;
      padding: 6px 4px;
      background: #f1f5f9;
      border: 1px solid #e2e8f0;
      border-radius: 6px;
      font-size: 13px;
      font-weight: 600;
      color: #64748b;
      cursor: pointer;
      text-align: center;
      transition: all 0.2s ease;
    }
    .step-btn.active {
      background: #1e2945;
      color: #ffffff;
      border-color: #1e2945;
    }
    .track-card {
      width: 100%;
      max-width: 480px;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 12px;
      padding: 16px 12px;
      display: flex;
      flex-direction: column;
      gap: 12px;
    }
    .stages-grid {
      display: grid;
      grid-template-columns: repeat(4, 1fr);
      gap: 6px;
      position: relative;
    }
    .stage-col {
      display: flex;
      flex-direction: column;
      align-items: center;
      padding: 8px 4px;
      border-radius: 8px;
      background: #ffffff;
      border: 1px solid #e2e8f0;
      transition: all 0.25s ease;
      position: relative;
    }
    .stage-col.highlight {
      border-color: #22b7ff;
      box-shadow: 0 0 0 2px rgba(34, 183, 255, 0.25);
    }
    .time-label {
      font-size: 13px;
      font-weight: 700;
      color: #1e2945;
      margin-bottom: 8px;
    }
    .arrow-area {
      height: 28px;
      display: flex;
      align-items: center;
      justify-content: flex-start;
      width: 100%;
      padding-left: 6px;
    }
    .vel-arrow {
      height: 8px;
      background: #22b7ff;
      border-radius: 4px;
      position: relative;
      transition: width 0.3s ease;
    }
    .vel-arrow::after {
      content: '';
      position: absolute;
      right: -3px;
      top: 50%;
      transform: translateY(-50%);
      width: 0;
      height: 0;
      border-top: 5px solid transparent;
      border-bottom: 5px solid transparent;
      border-left: 6px solid #22b7ff;
    }
    .car-symbol {
      font-size: 26px;
      line-height: 1;
      margin: 4px 0 8px;
      filter: drop-shadow(0 2px 3px rgba(0,0,0,0.08));
    }
    .vel-badge {
      font-size: 12px;
      font-weight: 700;
      color: #0284c7;
      background: #e0f2fe;
      padding: 3px 6px;
      border-radius: 4px;
      white-space: nowrap;
    }
    .road-strip {
      width: 100%;
      height: 8px;
      background: #334155;
      border-radius: 4px;
      position: relative;
      overflow: hidden;
    }
    .road-strip::after {
      content: '';
      position: absolute;
      left: 0;
      top: 3px;
      width: 100%;
      height: 2px;
      background-image: repeating-linear-gradient(90deg, #ffffff 0, #ffffff 12px, transparent 12px, transparent 24px);
    }
    .delta-row {
      display: grid;
      grid-template-columns: repeat(3, 1fr);
      gap: 6px;
      margin-top: 2px;
    }
    .delta-badge {
      text-align: center;
      font-size: 11px;
      font-weight: 700;
      color: #0369a1;
      background: #f0f9ff;
      border: 1px dashed #7dd3fc;
      border-radius: 6px;
      padding: 4px 2px;
    }
    .summary-bar {
      margin-top: 10px;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      background: #1e2945;
      color: #ffffff;
      padding: 8px 16px;
      border-radius: 8px;
      font-size: 13px;
      font-weight: 600;
    }
    .rate-pill {
      background: #22b7ff;
      color: #0f172a;
      padding: 2px 8px;
      border-radius: 4px;
      font-weight: 700;
    }
    .controls {
      display: flex;
      gap: 8px;
      margin-top: 8px;
    }
    .play-btn {
      padding: 6px 16px;
      border-radius: 6px;
      border: 1px solid #cbd5e1;
      background: #ffffff;
      font-size: 13px;
      font-weight: 600;
      color: #1e2945;
      cursor: pointer;
      display: flex;
      align-items: center;
      gap: 6px;
    }
  </style>
</head>
<body>

  <div class="stepper-nav">
    <button class="step-btn active" onclick="setStep(0)">t = 0s</button>
    <button class="step-btn" onclick="setStep(1)">t = 1s</button>
    <button class="step-btn" onclick="setStep(2)">t = 2s</button>
    <button class="step-btn" onclick="setStep(3)">t = 3s</button>
  </div>

  <div class="track-card">
    <div class="stages-grid">
      
      <div class="stage-col highlight" id="stage-0">
        <div class="time-label">0s</div>
        <div class="arrow-area">
          <div style="font-size: 11px; color: #94a3b8; font-weight: 600;">rest</div>
        </div>
        <div class="car-symbol">🏎️</div>
        <div class="vel-badge">0 m/s</div>
      </div>

      
      <div class="stage-col" id="stage-1">
        <div class="time-label">1s</div>
        <div class="arrow-area">
          <div class="vel-arrow" style="width: 30%;"></div>
        </div>
        <div class="car-symbol">🏎️</div>
        <div class="vel-badge">5 m/s</div>
      </div>

      
      <div class="stage-col" id="stage-2">
        <div class="time-label">2s</div>
        <div class="arrow-area">
          <div class="vel-arrow" style="width: 58%;"></div>
        </div>
        <div class="car-symbol">🏎️</div>
        <div class="vel-badge">10 m/s</div>
      </div>

      
      <div class="stage-col" id="stage-3">
        <div class="time-label">3s</div>
        <div class="arrow-area">
          <div class="vel-arrow" style="width: 86%;"></div>
        </div>
        <div class="car-symbol">🏎️</div>
        <div class="vel-badge">15 m/s</div>
      </div>
    </div>

    <div class="road-strip"></div>

    <div class="delta-row">
      <div class="delta-badge">+5 m/s</div>
      <div class="delta-badge">+5 m/s</div>
      <div class="delta-badge">+5 m/s</div>
    </div>
  </div>

  <div class="summary-bar">
    <span>Rate of change:</span>
    <span class="rate-pill">+5 m/s every second</span>
  </div>

  <div class="controls">
    <button class="play-btn" id="playBtn" onclick="togglePlay()">
      <span id="playIcon">⏸</span> Pause
    </button>
  </div>

  <script>
    let currentStep = 0;
    let playing = true;
    let timer = null;

    const buttons = document.querySelectorAll('.step-btn');
    const stages = document.querySelectorAll('.stage-col');
    const playIcon = document.getElementById('playIcon');
    const playBtn = document.getElementById('playBtn');

    function setStep(idx) {
      currentStep = idx;
      buttons.forEach((btn, i) => btn.classList.toggle('active', i === idx));
      stages.forEach((stage, i) => stage.classList.toggle('highlight', i <= idx));
    }

    function advance() {
      currentStep = (currentStep + 1) % 4;
      setStep(currentStep);
    }

    function startTimer() {
      if (timer) clearInterval(timer);
      timer = setInterval(advance, 1400);
    }

    function togglePlay() {
      playing = !playing;
      if (playing) {
        playIcon.textContent = '⏸';
        playBtn.childNodes[1].textContent = ' Pause';
        startTimer();
      } else {
        playIcon.textContent = '▶';
        playBtn.childNodes[1].textContent = ' Play';
        clearInterval(timer);
      }
    }

    startTimer();
  </script>
</body>
</html>

UK-GCSE-SCIENCE-PHYS-FM-01

Child standards (4)

Aligned learning resources

Related diagrams