<!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">
  <title>Waves Transfer Energy</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: #ffffff;
      width: 100%;
      height: 100%;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      padding: 12px 10px;
      user-select: none;
    }
    .top-bar {
      width: 100%;
      max-width: 350px;
      display: flex;
      align-items: center;
      justify-content: space-between;
      background: #eff6ff;
      border: 1px solid #bfdbfe;
      border-radius: 8px;
      padding: 8px 12px;
      margin-bottom: 8px;
    }
    .energy-label {
      font-size: 13px;
      font-weight: 700;
      color: #2563eb;
      display: flex;
      align-items: center;
      gap: 6px;
    }
    .energy-arrow {
      font-size: 16px;
      line-height: 1;
      animation: shiftRight 1.5s infinite linear;
    }
    @keyframes shiftRight {
      0% { transform: translateX(-2px); }
      50% { transform: translateX(3px); }
      100% { transform: translateX(-2px); }
    }
    .btn-toggle {
      background: #ffffff;
      border: 1px solid #93c5fd;
      color: #1d4ed8;
      border-radius: 6px;
      padding: 4px 10px;
      font-size: 12px;
      font-weight: 600;
      cursor: pointer;
      display: flex;
      align-items: center;
      gap: 4px;
    }
    .btn-toggle:hover {
      background: #f8fafc;
    }
    .sim-container {
      width: 100%;
      max-width: 350px;
      position: relative;
      background: #f0f9ff;
      border-radius: 12px;
      border: 1px solid #bae6fd;
      overflow: hidden;
    }
    svg {
      display: block;
      width: 100%;
      height: auto;
    }
    .summary-box {
      width: 100%;
      max-width: 350px;
      margin-top: 8px;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 8px;
      padding: 8px 10px;
      text-align: center;
      font-size: 12px;
      line-height: 1.4;
      color: #334155;
    }
    .summary-box strong {
      color: #0f172a;
    }
    .highlight-blue {
      color: #2563eb;
      font-weight: 600;
    }
    .highlight-amber {
      color: #d97706;
      font-weight: 600;
    }
  </style>
</head>
<body>

  
  <div class="top-bar">
    <div class="energy-label">
      <span>Energy Transfer</span>
      <span class="energy-arrow">➔</span>
    </div>
    <button id="playBtn" class="btn-toggle" aria-label="Pause/Play simulation">
      <span id="btnIcon">⏸</span> <span id="btnText">Pause</span>
    </button>
  </div>

  
  <div class="sim-container">
    <svg viewBox="0 0 350 200" preserveAspectRatio="xMidYMid meet">
      <defs>
        
        <linearGradient id="waterGrad" x1="0" y1="0" x2="0" y2="1">
          <stop offset="0%" stop-color="#38bdf8" stop-opacity="0.85" />
          <stop offset="100%" stop-color="#0284c7" stop-opacity="0.95" />
        </linearGradient>
        
        
        <pattern id="grid" width="20" height="20" patternUnits="userSpaceOnUse">
          <path d="M 20 0 L 0 0 0 20" fill="none" stroke="rgba(255,255,255,0.15)" stroke-width="1"/>
        </pattern>
      </defs>

      
      <line x1="0" y1="120" x2="350" y2="120" stroke="#cbd5e1" stroke-width="1" stroke-dasharray="4 4" />
      <text x="6" y="116" font-size="9" fill="#94a3b8" font-weight="600">Rest Position</text>

      
      <line x1="175" y1="15" x2="175" y2="195" stroke="#ef4444" stroke-width="1.5" stroke-dasharray="4 3" opacity="0.75" />
      <rect x="127" y="18" width="96" height="18" rx="4" fill="#fee2e2" stroke="#fca5a5" stroke-width="1" />
      <text x="175" y="30" font-size="10" fill="#dc2626" font-weight="700" text-anchor="middle">Fixed Position (x)</text>

      
      <g transform="translate(198, 90)">
        <line x1="0" y1="-25" x2="0" y2="25" stroke="#475569" stroke-width="1.5" marker-end="url(#arrow)" />
        <polygon points="0,-27 -3,-20 3,-20" fill="#475569" />
        <polygon points="0,27 -3,20 3,20" fill="#475569" />
        <text x="6" y="-6" font-size="9.5" fill="#334155" font-weight="600">Duck</text>
        <text x="6" y="5" font-size="9.5" fill="#334155" font-weight="600">oscillates</text>
        <text x="6" y="16" font-size="9.5" fill="#334155" font-weight="600">↕ vertically</text>
      </g>

      
      <path id="waterPath" fill="url(#waterGrad)" d="" />
      <path id="waterGridOverlay" fill="url(#grid)" d="" />
      
      
      <path id="waterSurface" fill="none" stroke="#e0f2fe" stroke-width="3" stroke-linecap="round" d="" />

      
      <g id="particles"></g>

      
      <g id="duckGroup" transform="translate(175, 120)">
        
        <ellipse cx="0" cy="14" rx="16" ry="4" fill="#0284c7" opacity="0.4" />
        
        
        
        <path d="M -16,6 C -20,0 -16,-6 -8,-6 C 2,-6 14,0 16,8 C 16,14 6,16 -4,16 C -12,16 -16,12 -16,6 Z" fill="#fbbf24" stroke="#d97706" stroke-width="1.5" />
        
        <path d="M -6,4 C -2,0 6,1 7,6 C 7,9 1,11 -4,10 Z" fill="#f59e0b" />
        
        <circle cx="10" cy="-6" r="8.5" fill="#fbbf24" stroke="#d97706" stroke-width="1.5" />
        
        <circle cx="13" cy="-8" r="1.8" fill="#1e2945" />
        <circle cx="13.6" cy="-8.6" r="0.6" fill="#ffffff" />
        
        <path d="M 16,-6 Q 24,-4 20,0 Q 16,-1 16,-3 Z" fill="#ea580c" stroke="#c2410c" stroke-width="0.8" />
      </g>

      
      <circle id="duckAnchorDot" cx="175" cy="120" r="3.5" fill="#dc2626" />
    </svg>
  </div>

  
  <div class="summary-box">
    <strong>Key Rule:</strong> Waves transfer <span class="highlight-blue">energy</span> across the medium, but matter (<span class="highlight-amber">the duck &amp; water</span>) only oscillates in place.
  </div>

  <script>
    const waterPath = document.getElementById('waterPath');
    const waterSurface = document.getElementById('waterSurface');
    const waterGridOverlay = document.getElementById('waterGridOverlay');
    const duckGroup = document.getElementById('duckGroup');
    const duckAnchorDot = document.getElementById('duckAnchorDot');
    const playBtn = document.getElementById('playBtn');
    const btnIcon = document.getElementById('btnIcon');
    const btnText = document.getElementById('btnText');
    const particlesContainer = document.getElementById('particles');

    // Create 5 reference water particles along the wave to show matter stays in column
    const particleXPositions = [55, 115, 175, 235, 295];
    const particleElems = [];

    particleXPositions.forEach((x, idx) => {
      // Small vertical guide line for particle
      if (x !== 175) {
        const line = document.createElementNS('http://www.w3.org/2000/svg', 'line');
        line.setAttribute('x1', x);
        line.setAttribute('x2', x);
        line.setAttribute('y1', 95);
        line.setAttribute('y2', 145);
        line.setAttribute('stroke', '#38bdf8');
        line.setAttribute('stroke-width', '1');
        line.setAttribute('stroke-dasharray', '2 2');
        line.setAttribute('opacity', '0.5');
        particlesContainer.appendChild(line);
      }

      // Particle dot
      const circle = document.createElementNS('http://www.w3.org/2000/svg', 'circle');
      circle.setAttribute('cx', x);
      circle.setAttribute('cy', 120);
      circle.setAttribute('r', x === 175 ? '3.5' : '3');
      circle.setAttribute('fill', x === 175 ? '#d97706' : '#ffffff');
      circle.setAttribute('stroke', x === 175 ? '#b45309' : '#0284c7');
      circle.setAttribute('stroke-width', '1.5');
      particlesContainer.appendChild(circle);
      particleElems.push({ el: circle, x: x });
    });

    // Wave parameters
    const amplitude = 18;       // vertical displacement peak
    const wavelength = 140;     // pixel distance per full cycle
    const restY = 120;          // resting water level
    const speed = 0.055;        // propagation speed
    let phase = 0;
    let isRunning = true;
    let animId = null;

    function getWaveY(x, p) {
      // Traveling wave moving Left -> Right: y = A * sin(k*x - phase)
      const k = (2 * Math.PI) / wavelength;
      return restY + amplitude * Math.sin(k * x - p);
    }

    function getWaveSlope(x, p) {
      const k = (2 * Math.PI) / wavelength;
      // dy/dx = A * k * cos(k*x - phase)
      return amplitude * k * Math.cos(k * x - p);
    }

    function draw() {
      // Build smooth wave path using sampled points
      let d = `M 0,200 L 0,${getWaveY(0, phase).toFixed(1)}`;
      let surfaceD = `M 0,${getWaveY(0, phase).toFixed(1)}`;

      const step = 4;
      for (let x = step; x <= 350; x += step) {
        const y = getWaveY(x, phase).toFixed(1);
        d += ` L ${x},${y}`;
        surfaceD += ` L ${x},${y}`;
      }

      d += ` L 350,200 Z`;

      waterPath.setAttribute('d', d);
      waterGridOverlay.setAttribute('d', d);
      waterSurface.setAttribute('d', surfaceD);

      // Calculate exact duck position and tilt on the water
      const duckX = 175;
      const duckY = getWaveY(duckX, phase);
      const slope = getWaveSlope(duckX, phase);
      // Slight tilt corresponding to wave angle (in degrees)
      const angleDeg = (Math.atan(slope) * (180 / Math.PI) * 0.45).toFixed(2);

      duckGroup.setAttribute('transform', `translate(${duckX}, ${duckY.toFixed(1)}) rotate(${angleDeg})`);
      duckAnchorDot.setAttribute('cy', duckY.toFixed(1));

      // Update particle positions (oscillate only vertically)
      particleElems.forEach(p => {
        const py = getWaveY(p.x, phase);
        p.el.setAttribute('cy', py.toFixed(1));
      });

      if (isRunning) {
        phase += speed;
        animId = requestAnimationFrame(draw);
      }
    }

    // Toggle simulation state
    playBtn.addEventListener('click', () => {
      isRunning = !isRunning;
      if (isRunning) {
        btnIcon.textContent = '⏸';
        btnText.textContent = 'Pause';
        draw();
      } else {
        btnIcon.textContent = '▶';
        btnText.textContent = 'Play';
        cancelAnimationFrame(animId);
      }
    });

    // Start simulation loop
    draw();
  </script>
</body>
</html>

Waves Transfer Energy Without Moving Matter

<!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;
      user-select: none;
    }

    body {
      width: 100%;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      color: #1e293b;
      background: transparent;
      padding: 8px 12px 14px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 8px;
    }

    .header-bar {
      width: 100%;
      max-width: 540px;
      display: flex;
      align-items: center;
      justify-content: space-between;
      padding: 2px 4px;
    }

    .energy-banner {
      display: inline-flex;
      align-items: center;
      gap: 6px;
      font-size: 13px;
      font-weight: 700;
      color: #0369a1;
      background: #e0f2fe;
      padding: 4px 10px;
      border-radius: 999px;
    }

    .energy-arrow {
      display: inline-block;
      font-size: 15px;
      animation: nudgeRight 1.5s ease-in-out infinite;
    }

    @keyframes nudgeRight {
      0%, 100% { transform: translateX(0); }
      50% { transform: translateX(4px); }
    }

    .controls {
      display: flex;
      gap: 6px;
    }

    .btn-ctrl {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      color: #334155;
      font-size: 12px;
      font-weight: 600;
      padding: 4px 10px;
      border-radius: 6px;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 4px;
      transition: background 0.2s, border-color 0.2s;
    }

    .btn-ctrl:hover {
      background: #e2e8f0;
      border-color: #94a3b8;
    }

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

    .svg-container {
      width: 100%;
      max-width: 540px;
      aspect-ratio: 540 / 380;
      position: relative;
    }

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

    .summary-box {
      width: 100%;
      max-width: 540px;
      text-align: center;
      font-size: 13px;
      font-weight: 600;
      color: #475569;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      padding: 6px 12px;
      border-radius: 8px;
    }

    .summary-box strong {
      color: #ef4444;
    }
  </style>
</head>
<body>

  <div class="header-bar">
    <div class="energy-banner">
      <span>Wave pulse / Energy travels right</span>
      <span class="energy-arrow">➔</span>
    </div>
    <div class="controls">
      <button class="btn-ctrl" id="toggleSpeed">0.5× Slow</button>
      <button class="btn-ctrl" id="togglePlay">⏸ Pause</button>
    </div>
  </div>

  <div class="svg-container">
    <svg viewBox="0 0 540 380" id="waveSvg">
      <defs>
        
        <linearGradient id="trackGrad" x1="0%" y1="0%" x2="100%" y2="0%">
          <stop offset="0%" stop-color="#f8fafc" />
          <stop offset="100%" stop-color="#f1f5f9" />
        </linearGradient>

        <marker id="arrowRight" viewBox="0 0 8 8" refX="6" refY="4" markerWidth="6" markerHeight="6" orient="auto">
          <path d="M 0 1 L 7 4 L 0 7 z" fill="#0284c7" />
        </marker>
        <marker id="arrowRedV" viewBox="0 0 8 8" refX="4" refY="4" markerWidth="6" markerHeight="6" orient="auto">
          <path d="M 1 0 L 4 7 L 7 0 z" fill="#ef4444" />
        </marker>
        <marker id="arrowRedH" viewBox="0 0 8 8" refX="4" refY="4" markerWidth="6" markerHeight="6" orient="auto">
          <path d="M 0 1 L 7 4 L 0 7 z" fill="#ef4444" />
        </marker>
      </defs>

      
      <g id="transverseSection">
        
        <rect x="10" y="8" width="520" height="165" rx="10" fill="url(#trackGrad)" stroke="#e2e8f0" stroke-width="1" />
        
        
        <rect x="22" y="18" width="135" height="24" rx="5" fill="#e0f2fe" />
        <text x="28" y="34" font-size="12" font-weight="700" fill="#0369a1">TRANSVERSE WAVE</text>
        
        
        <line x1="400" y1="30" x2="495" y2="30" stroke="#0284c7" stroke-width="2.5" marker-end="url(#arrowRight)" />
        <text x="350" y="34" font-size="11" font-weight="600" fill="#0284c7">Energy ➔</text>

        
        <line x1="30" y1="95" x2="510" y2="95" stroke="#cbd5e1" stroke-width="1.5" stroke-dasharray="4,4" />
        <text x="475" y="112" font-size="10" fill="#94a3b8">Rest line</text>

        
        <line x1="270" y1="42" x2="270" y2="152" stroke="#fca5a5" stroke-width="1.5" stroke-dasharray="3,3" />
        
        
        <path id="transverseSpring" d="" fill="none" stroke="#475569" stroke-width="3" stroke-linecap="round" stroke-linejoin="round" />

        
        <circle cx="270" cy="95" r="3" fill="#cbd5e1" />

        
        <g id="ribbonTransverse" transform="translate(270, 95)">
          
          <circle cx="0" cy="0" r="6" fill="#ef4444" stroke="#ffffff" stroke-width="1.5" />
          <path d="M -3 3 L -7 14 L -2 12 L 0 16 L 2 12 L 7 14 L 3 3" fill="#ef4444" />
        </g>

        
        <g transform="translate(285, 95)">
          <line x1="0" y1="-32" x2="0" y2="32" stroke="#ef4444" stroke-width="2" />
          <polygon points="0,-36 -4,-28 4,-28" fill="#ef4444" />
          <polygon points="0,36 -4,28 4,28" fill="#ef4444" />
          <text x="10" y="-8" font-size="11" font-weight="700" fill="#ef4444">Ribbon vibrates ↕</text>
          <text x="10" y="8" font-size="10.5" font-weight="600" fill="#64748b">Perpendicular</text>
        </g>
      </g>

      
      <g id="longitudinalSection" transform="translate(0, 185)">
        
        <rect x="10" y="8" width="520" height="165" rx="10" fill="url(#trackGrad)" stroke="#e2e8f0" stroke-width="1" />

        
        <rect x="22" y="18" width="155" height="24" rx="5" fill="#fef3c7" />
        <text x="28" y="34" font-size="12" font-weight="700" fill="#b45309">LONGITUDINAL WAVE</text>

        
        <line x1="400" y1="30" x2="495" y2="30" stroke="#0284c7" stroke-width="2.5" marker-end="url(#arrowRight)" />
        <text x="350" y="34" font-size="11" font-weight="600" fill="#0284c7">Energy ➔</text>

        
        <line x1="30" y1="95" x2="510" y2="95" stroke="#cbd5e1" stroke-width="1.5" stroke-dasharray="4,4" />

        
        <line x1="270" y1="45" x2="270" y2="145" stroke="#fca5a5" stroke-width="1.5" stroke-dasharray="3,3" />
        <circle cx="270" cy="95" r="3" fill="#cbd5e1" />

        
        <g id="longitudinalCoils"></g>

        
        <g id="ribbonLongitudinal" transform="translate(270, 95)">
          <circle cx="0" cy="0" r="6" fill="#ef4444" stroke="#ffffff" stroke-width="1.5" />
          <path d="M -3 3 L -7 14 L -2 12 L 0 16 L 2 12 L 7 14 L 3 3" fill="#ef4444" />
        </g>

        
        <g transform="translate(270, 138)">
          <line x1="-30" y1="0" x2="30" y2="0" stroke="#ef4444" stroke-width="2" />
          <polygon points="-34,0 -26,-4 -26,4" fill="#ef4444" />
          <polygon points="34,0 26,-4 26,4" fill="#ef4444" />
          <text x="0" y="16" font-size="11" font-weight="700" fill="#ef4444" text-anchor="middle">Ribbon vibrates ↔</text>
          <text x="0" y="29" font-size="10.5" font-weight="600" fill="#64748b" text-anchor="middle">Parallel</text>
        </g>
      </g>
    </svg>
  </div>

  <div class="summary-box">
    <strong>Red ribbon stays in place</strong> — energy moves, matter does not!
  </div>

  <script>
    // Slinky parameters
    const NUM_COILS = 33;
    const X_START = 40;
    const X_END = 500;
    const COIL_SPACING = (X_END - X_START) / (NUM_COILS - 1);
    const MID_INDEX = 16; // Coil with the ribbon at x = 270

    const tSpringPath = document.getElementById('transverseSpring');
    const lCoilsGroup = document.getElementById('longitudinalCoils');
    const ribbonT = document.getElementById('ribbonTransverse');
    const ribbonL = document.getElementById('ribbonLongitudinal');
    const togglePlayBtn = document.getElementById('togglePlay');
    const toggleSpeedBtn = document.getElementById('toggleSpeed');

    // Create persistent coil elements for longitudinal spring
    const lCoilElements = [];
    for (let i = 0; i < NUM_COILS; i++) {
      const path = document.createElementNS('http://www.w3.org/2000/svg', 'path');
      path.setAttribute('fill', 'none');
      path.setAttribute('stroke', '#475569');
      path.setAttribute('stroke-width', '3');
      path.setAttribute('stroke-linecap', 'round');
      lCoilsGroup.appendChild(path);
      lCoilElements.push(path);
    }

    // Animation state
    let isPlaying = true;
    let speedMultiplier = 1.0;
    let lastTime = performance.now();
    let pulseX = -60; // Traveling pulse position

    const PULSE_SPEED = 140; // px/sec
    const PULSE_SIGMA = 42;  // width of pulse
    const AMP_TRANSVERSE = 38; // px vertical displacement
    const AMP_LONGITUDINAL = 26; // px horizontal displacement

    function animate(now) {
      const dt = (now - lastTime) / 1000;
      lastTime = now;

      if (isPlaying) {
        pulseX += PULSE_SPEED * speedMultiplier * dt;
        if (pulseX > X_END + 90) {
          pulseX = X_START - 90;
        }
      }

      // 1. UPDATE TRANSVERSE WAVE
      let tPathD = `M ${X_START} 95`;
      let ribbonTY = 95;

      for (let i = 0; i < NUM_COILS; i++) {
        const xRest = X_START + i * COIL_SPACING;
        // Gaussian crest pulse
        const dist = xRest - pulseX;
        const dispY = AMP_TRANSVERSE * Math.exp(-(dist * dist) / (2 * PULSE_SIGMA * PULSE_SIGMA));
        const curY = 95 - dispY;

        if (i === MID_INDEX) {
          ribbonTY = curY;
        }

        // Draw helical spring loops
        const prevX = i === 0 ? X_START : X_START + (i - 1) * COIL_SPACING;
        const midX = (prevX + xRest) / 2;
        tPathD += ` Q ${midX} ${curY - 14}, ${xRest} ${curY}`;
      }
      tSpringPath.setAttribute('d', tPathD);
      ribbonT.setAttribute('transform', `translate(270, ${ribbonTY})`);

      // 2. UPDATE LONGITUDINAL WAVE
      let ribbonLX = 270;

      for (let i = 0; i < NUM_COILS; i++) {
        const xRest = X_START + i * COIL_SPACING;
        // Derivative of Gaussian creates a clean localized compression pulse
        const dist = xRest - pulseX;
        const dispX = -AMP_LONGITUDINAL * (dist / PULSE_SIGMA) * Math.exp(-(dist * dist) / (2 * PULSE_SIGMA * PULSE_SIGMA));
        const curX = xRest + dispX;

        if (i === MID_INDEX) {
          ribbonLX = curX;
        }

        // Render each slinky coil as a vertical elliptical ring
        const ry = 22;
        const rx = 5.5;
        const coilD = `M ${curX} ${95 - ry} C ${curX + rx} ${95 - ry}, ${curX + rx} ${95 + ry}, ${curX} ${95 + ry} C ${curX - rx} ${95 + ry}, ${curX - rx} ${95 - ry}, ${curX} ${95 - ry}`;
        lCoilElements[i].setAttribute('d', coilD);

        // Highlight compressed coils slightly
        const compressionIntensity = Math.abs(dispX) / AMP_LONGITUDINAL;
        if (compressionIntensity > 0.4 && Math.abs(dist) < PULSE_SIGMA * 1.2) {
          lCoilElements[i].setAttribute('stroke', '#0284c7');
        } else {
          lCoilElements[i].setAttribute('stroke', '#475569');
        }
      }
      ribbonL.setAttribute('transform', `translate(${ribbonLX}, 95)`);

      requestAnimationFrame(animate);
    }

    // Toggle Play/Pause
    togglePlayBtn.addEventListener('click', () => {
      isPlaying = !isPlaying;
      togglePlayBtn.textContent = isPlaying ? '⏸ Pause' : '▶ Play';
      togglePlayBtn.classList.toggle('active', !isPlaying);
    });

    // Toggle Speed
    toggleSpeedBtn.addEventListener('click', () => {
      if (speedMultiplier === 1.0) {
        speedMultiplier = 0.4;
        toggleSpeedBtn.textContent = '1.0× Normal';
        toggleSpeedBtn.classList.add('active');
      } else {
        speedMultiplier = 1.0;
        toggleSpeedBtn.textContent = '0.5× Slow';
        toggleSpeedBtn.classList.remove('active');
      }
    });

    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">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }
    body {
      background-color: #f8f9fa;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
      color: #1e293b;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
      padding: 12px 8px;
      user-select: none;
    }
    .main-stage {
      width: 100%;
      max-width: 600px;
      position: relative;
      display: flex;
      flex-direction: column;
      align-items: center;
    }
    .svg-container {
      width: 100%;
      height: auto;
      max-height: 280px;
      overflow: visible;
    }
    
    /* Motion labels & arrows container */
    .indicators {
      width: 100%;
      max-width: 540px;
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 8px;
      margin-top: 4px;
      padding: 0 4px;
    }
    .indicator-card {
      display: flex;
      align-items: center;
      gap: 8px;
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 8px;
      padding: 6px 10px;
    }
    .badge-icon {
      width: 24px;
      height: 24px;
      border-radius: 6px;
      display: flex;
      align-items: center;
      justify-content: center;
      font-weight: 700;
      font-size: 15px;
      flex-shrink: 0;
    }
    .badge-energy {
      background: #eff6ff;
      color: #2563eb;
      border: 1px solid #bfdbfe;
    }
    .badge-matter {
      background: #fff1f2;
      color: #f43f5e;
      border: 1px solid #fecdd3;
    }
    .card-text {
      font-size: 12px;
      line-height: 1.25;
      font-weight: 600;
    }
    .card-sub {
      font-size: 10.5px;
      font-weight: 400;
      color: #64748b;
    }

    /* Controls */
    .controls {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 12px;
      margin-top: 10px;
      width: 100%;
    }
    .btn {
      background: #ffffff;
      border: 1px solid #cbd5e1;
      color: #1e293b;
      border-radius: 6px;
      padding: 6px 14px;
      font-size: 13px;
      font-weight: 600;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 6px;
      transition: background 0.15s, border-color 0.15s;
    }
    .btn:active {
      background: #f1f5f9;
      border-color: #94a3b8;
    }
    .step-track {
      display: flex;
      gap: 5px;
    }
    .dot-step {
      width: 8px;
      height: 8px;
      border-radius: 50%;
      background: #cbd5e1;
      cursor: pointer;
      transition: background 0.2s;
    }
    .dot-step.active {
      background: #2563eb;
      transform: scale(1.25);
    }
  </style>
</head>
<body>

  <div class="main-stage">
    
    <svg class="svg-container" viewBox="0 0 560 250">
      <defs>
        
        <linearGradient id="energyGrad" x1="0%" y1="0%" x2="100%" y2="0%">
          <stop offset="0%" stop-color="#3b82f6" stop-opacity="0.3"/>
          <stop offset="70%" stop-color="#2563eb" stop-opacity="1"/>
          <stop offset="100%" stop-color="#1d4ed8" stop-opacity="1"/>
        </linearGradient>

        <marker id="arrowRight" markerWidth="8" markerHeight="8" refX="5" refY="4" orient="auto">
          <polygon points="0 1, 6 4, 0 7" fill="#2563eb"/>
        </marker>
        <marker id="arrowUpCoral" markerWidth="6" markerHeight="6" refX="3" refY="3" orient="auto">
          <polygon points="0 5, 3 1, 6 5" fill="#f43f5e"/>
        </marker>
        <marker id="arrowDownCoral" markerWidth="6" markerHeight="6" refX="3" refY="3" orient="auto">
          <polygon points="0 1, 3 5, 6 1" fill="#f43f5e"/>
        </marker>
      </defs>

      
      <path d="M 15 200 L 545 200" stroke="#cbd5e1" stroke-width="4" stroke-linecap="round"/>
      <path d="M 25 212 L 535 212" stroke="#e2e8f0" stroke-width="2" stroke-dasharray="6,6"/>

      
      <g id="fans-group"></g>

      
      <g id="vertical-indicator" transform="translate(0, 0)" style="transition: transform 0.25s ease;">
        <line x1="0" y1="28" x2="0" y2="78" stroke="#f43f5e" stroke-width="2" stroke-dasharray="3,3" marker-start="url(#arrowUpCoral)" marker-end="url(#arrowDownCoral)"/>
        <rect x="-38" y="6" width="76" height="18" rx="4" fill="#fff1f2" stroke="#fecdd3" stroke-width="1"/>
        <text x="0" y="19" font-size="9.5" font-weight="700" fill="#e11d48" text-anchor="middle">Oscillates Up/Down</text>
      </g>

      
      <g id="energy-arrow-group" transform="translate(0, 222)">
        <line x1="45" y1="10" x2="495" y2="10" stroke="url(#energyGrad)" stroke-width="4" marker-end="url(#arrowRight)" stroke-linecap="round"/>
        <rect x="180" y="1" width="200" height="18" rx="4" fill="#ffffff" stroke="#bfdbfe" stroke-width="1"/>
        <text x="280" y="14" font-size="10.5" font-weight="700" fill="#2563eb" text-anchor="middle">Wave Motion (Energy Transfer) →</text>
      </g>
    </svg>

    
    <div class="indicators">
      <div class="indicator-card">
        <div class="badge-icon badge-energy">→</div>
        <div>
          <div class="card-text" style="color: #1d4ed8;">Wave Direction</div>
          <div class="card-sub">Energy moves horizontally</div>
        </div>
      </div>
      <div class="indicator-card">
        <div class="badge-icon badge-matter">↕</div>
        <div>
          <div class="card-text" style="color: #be123c;">Fan Motion</div>
          <div class="card-sub">Matter stays in place</div>
        </div>
      </div>
    </div>

    
    <div class="controls">
      <button class="btn" id="playBtn" onclick="togglePlay()">
        <span id="playIcon">⏸</span> <span id="playText">Pause</span>
      </button>
      <div class="step-track" id="stepTrack"></div>
      <button class="btn" onclick="stepForward()">Step ❯</button>
    </div>
  </div>

  <script>
    const NUM_FANS = 8;
    const SPACING = 60;
    const START_X = 70;
    
    const fansGroup = document.getElementById('fans-group');
    const stepTrack = document.getElementById('stepTrack');
    const vertIndicator = document.getElementById('vertical-indicator');
    const playIcon = document.getElementById('playIcon');
    const playText = document.getElementById('playText');

    let currentWaveIndex = 0;
    let isPlaying = true;
    let timer = null;

    // Render Fans and Stepper Dots
    for (let i = 0; i < NUM_FANS; i++) {
      const x = START_X + i * SPACING;
      
      // SVG Fan element
      const g = document.createElementNS('http://www.w3.org/2000/svg', 'g');
      g.setAttribute('id', `fan-${i}`);
      g.setAttribute('transform', `translate(${x}, 0)`);
      g.style.cursor = 'pointer';
      g.onclick = () => jumpTo(i);

      // Fan visuals: Seat, Body group
      g.innerHTML = `
        
        <rect x="-14" y="195" width="28" height="5" rx="2" fill="#94a3b8"/>
        <rect x="-12" y="175" width="4" height="20" rx="1" fill="#cbd5e1"/>
        <rect x="8" y="175" width="4" height="20" rx="1" fill="#cbd5e1"/>

        
        <g id="figure-${i}" style="transition: transform 0.28s cubic-bezier(0.34, 1.3, 0.64, 1);">
          
          <circle id="head-${i}" cx="0" cy="148" r="8" fill="#1e293b"/>
          
          
          <line id="torso-${i}" x1="0" y1="156" x2="0" y2="182" stroke="#1e293b" stroke-width="4" stroke-linecap="round"/>
          
          
          <path id="arms-${i}" d="M -12 168 L 0 160 L 12 168" stroke="#2563eb" stroke-width="3" fill="none" stroke-linecap="round" stroke-linejoin="round"/>
          
          
          <path id="legs-${i}" d="M -8 198 L -6 182 L 0 182 L 6 182 L 8 198" stroke="#1e293b" stroke-width="3.5" fill="none" stroke-linecap="round" stroke-linejoin="round"/>
        </g>
      `;
      fansGroup.appendChild(g);

      // Dot for step track
      const dot = document.createElement('div');
      dot.className = 'dot-step' + (i === 0 ? ' active' : '');
      dot.onclick = () => jumpTo(i);
      stepTrack.appendChild(dot);
    }

    function setFanState(index, phase) {
      // phase: 0 = seated, 1 = standing up, 0.4 = rising/falling
      const fig = document.getElementById(`figure-${index}`);
      const arms = document.getElementById(`arms-${index}`);
      const legs = document.getElementById(`legs-${index}`);
      const head = document.getElementById(`head-${index}`);
      const torso = document.getElementById(`torso-${index}`);

      if (phase === 1) {
        // FULLY STANDING + ARMS UP (PEAK)
        fig.setAttribute('transform', 'translate(0, -42)');
        arms.setAttribute('d', 'M -14 136 L 0 156 L 14 136');
        arms.setAttribute('stroke', '#f43f5e');
        arms.setAttribute('stroke-width', '3.5');
        legs.setAttribute('d', 'M -5 224 L -4 182 L 0 182 L 4 182 L 5 224');
        head.setAttribute('fill', '#f43f5e');
        torso.setAttribute('stroke', '#f43f5e');
      } else if (phase > 0) {
        // MID-TRANSITION
        fig.setAttribute('transform', 'translate(0, -18)');
        arms.setAttribute('d', 'M -16 156 L 0 158 L 16 156');
        arms.setAttribute('stroke', '#3b82f6');
        arms.setAttribute('stroke-width', '3');
        legs.setAttribute('d', 'M -7 210 L -5 182 L 0 182 L 5 182 L 7 210');
        head.setAttribute('fill', '#1e293b');
        torso.setAttribute('stroke', '#1e293b');
      } else {
        // SITTING
        fig.setAttribute('transform', 'translate(0, 0)');
        arms.setAttribute('d', 'M -12 168 L 0 160 L 12 168');
        arms.setAttribute('stroke', '#2563eb');
        arms.setAttribute('stroke-width', '3');
        legs.setAttribute('d', 'M -8 198 L -6 182 L 0 182 L 6 182 L 8 198');
        head.setAttribute('fill', '#1e293b');
        torso.setAttribute('stroke', '#1e293b');
      }
    }

    function renderState(activeIdx) {
      for (let i = 0; i < NUM_FANS; i++) {
        const dist = Math.abs(i - activeIdx);
        if (dist === 0) {
          setFanState(i, 1);
        } else if (dist === 1) {
          setFanState(i, 0.4);
        } else {
          setFanState(i, 0);
        }
      }

      // Update vertical indicator position
      const activeX = START_X + activeIdx * SPACING;
      vertIndicator.setAttribute('transform', `translate(${activeX}, 0)`);

      // Update step dots
      const dots = document.querySelectorAll('.dot-step');
      dots.forEach((dot, idx) => {
        dot.classList.toggle('active', idx === activeIdx);
      });
    }

    function nextStep() {
      currentWaveIndex = (currentWaveIndex + 1) % NUM_FANS;
      renderState(currentWaveIndex);
    }

    function stepForward() {
      pause();
      nextStep();
    }

    function jumpTo(idx) {
      pause();
      currentWaveIndex = idx;
      renderState(currentWaveIndex);
    }

    function play() {
      isPlaying = true;
      playIcon.textContent = '⏸';
      playText.textContent = 'Pause';
      if (timer) clearInterval(timer);
      timer = setInterval(nextStep, 550);
    }

    function pause() {
      isPlaying = false;
      playIcon.textContent = '▶';
      playText.textContent = 'Play';
      if (timer) {
        clearInterval(timer);
        timer = null;
      }
    }

    function togglePlay() {
      if (isPlaying) {
        pause();
      } else {
        play();
      }
    }

    // Initialize
    renderState(0);
    play();
  </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>Waves Transfer Energy</title>
  <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: #0f172a;
      padding: 12px;
      display: flex;
      flex-direction: column;
      gap: 12px;
    }
    
    .grid {
      display: grid;
      grid-template-columns: 1fr;
      gap: 12px;
      width: 100%;
    }
    @media (min-width: 580px) {
      .grid {
        grid-template-columns: 1.35fr 1fr;
      }
    }

    .card-panel {
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 12px;
      padding: 12px;
      box-shadow: 0 2px 8px rgba(15, 23, 42, 0.05);
      display: flex;
      flex-direction: column;
      gap: 8px;
    }

    .card-title {
      font-size: 13px;
      font-weight: 700;
      text-transform: uppercase;
      letter-spacing: 0.5px;
      color: #64748b;
      display: flex;
      align-items: center;
      justify-content: space-between;
    }

    .canvas-container {
      position: relative;
      width: 100%;
      height: 180px;
      background: linear-gradient(180deg, #f0f9ff 0%, #fefce8 65%, #fef08a 100%);
      border-radius: 8px;
      overflow: hidden;
      border: 1px solid #cbd5e1;
    }

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

    .energy-banner {
      position: absolute;
      top: 8px;
      left: 12px;
      right: 12px;
      display: flex;
      align-items: center;
      justify-content: space-between;
      background: rgba(255, 255, 255, 0.92);
      backdrop-filter: blur(4px);
      padding: 4px 10px;
      border-radius: 20px;
      border: 1px solid #fed7aa;
      font-size: 12px;
      font-weight: 700;
      color: #d97706;
      box-shadow: 0 1px 4px rgba(0,0,0,0.05);
      pointer-events: none;
    }

    .energy-arrow {
      display: inline-flex;
      align-items: center;
      gap: 4px;
      color: #d97706;
      animation: pulseRight 1.5s infinite ease-in-out;
    }

    @keyframes pulseRight {
      0%, 100% { transform: translateX(0); }
      50% { transform: translateX(4px); }
    }

    .stalk-tag {
      position: absolute;
      bottom: 8px;
      left: 50%;
      transform: translateX(-50%);
      background: rgba(15, 23, 42, 0.9);
      color: #ffffff;
      padding: 3px 8px;
      border-radius: 12px;
      font-size: 11px;
      font-weight: 600;
      white-space: nowrap;
      pointer-events: none;
    }

    .key-points {
      display: flex;
      flex-direction: column;
      gap: 8px;
      justify-content: center;
      height: 100%;
    }

    .principle-box {
      background: #fffbeb;
      border: 1px solid #fde68a;
      border-radius: 8px;
      padding: 10px;
    }

    .principle-heading {
      font-size: 11px;
      font-weight: 800;
      text-transform: uppercase;
      letter-spacing: 0.5px;
      color: #b45309;
      margin-bottom: 4px;
    }

    .principle-text {
      font-size: 13.5px;
      line-height: 1.35;
      font-weight: 600;
      color: #0f172a;
    }

    .row-item {
      display: flex;
      align-items: flex-start;
      gap: 8px;
      background: #f8fafc;
      padding: 8px 10px;
      border-radius: 8px;
      border-left: 3px solid #cbd5e1;
    }

    .row-item.matter {
      border-left-color: #0f172a;
    }

    .row-item.energy {
      border-left-color: #d97706;
    }

    .badge {
      font-size: 11px;
      font-weight: 700;
      padding: 2px 6px;
      border-radius: 4px;
      white-space: nowrap;
    }

    .badge-matter {
      background: #0f172a;
      color: #ffffff;
    }

    .badge-energy {
      background: #d97706;
      color: #ffffff;
    }

    .row-desc {
      font-size: 12.5px;
      color: #334155;
      font-weight: 500;
    }

    .btn-controls {
      display: flex;
      gap: 6px;
      align-items: center;
      margin-top: 2px;
    }

    .btn {
      appearance: none;
      border: 1px solid #cbd5e1;
      background: #f8fafc;
      color: #0f172a;
      padding: 4px 10px;
      font-size: 12px;
      font-weight: 600;
      border-radius: 6px;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 4px;
    }

    .btn:hover {
      background: #f1f5f9;
      border-color: #94a3b8;
    }
  </style>
</head>
<body>

  <div class="grid">
    
    <div class="card-panel">
      <div class="card-title">
        <span>Leonardo's Wheat Field</span>
        <div class="btn-controls">
          <button class="btn" id="toggleBtn" onclick="togglePlay()">⏸ Pause</button>
        </div>
      </div>

      <div class="canvas-container">
        <canvas id="wheatCanvas"></canvas>
        <div class="energy-banner">
          <span>Wave / Ripple</span>
          <span class="energy-arrow">Energy travels →</span>
        </div>
        <div class="stalk-tag">↔ Stalk oscillates in place (Matter)</div>
      </div>
    </div>

    
    <div class="card-panel">
      <div class="card-title">Key Principle</div>
      <div class="key-points">
        <div class="principle-box">
          <div class="principle-heading">GCSE Physics Summary</div>
          <div class="principle-text">
            Matter oscillates around a <b>fixed position</b>, while energy travels <b>forward</b>.
          </div>
        </div>

        <div class="row-item matter">
          <span class="badge badge-matter">Matter</span>
          <div class="row-desc"><b>Wheat stalks</b> stay rooted; sway back and forth in place.</div>
        </div>

        <div class="row-item energy">
          <span class="badge badge-energy">Energy</span>
          <div class="row-desc"><b>Wave ripple</b> travels continuously across the whole field.</div>
        </div>
      </div>
    </div>
  </div>

  <script>
    const canvas = document.getElementById('wheatCanvas');
    const ctx = canvas.getContext('2d');
    let isPlaying = true;
    let t = 0;
    let animId = null;

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

    const numStalks = 22;

    function draw() {
      const w = canvas.parentElement.clientWidth;
      const h = canvas.parentElement.clientHeight;

      ctx.clearRect(0, 0, w, h);

      const groundY = h - 22;
      const stalkHeight = 75;
      const trackedIdx = Math.floor(numStalks / 2);

      // Draw subtle ground strip
      ctx.fillStyle = '#ca8a04';
      ctx.fillRect(0, groundY, w, 22);

      // Draw each stalk
      for (let i = 0; i < numStalks; i++) {
        const xBase = (w / (numStalks + 1)) * (i + 1);
        const isTracked = (i === trackedIdx);

        // Travelling wave formula: phase = (x / lambda) - omega * t
        const spatialPhase = (i / numStalks) * (Math.PI * 2.5);
        const waveAngle = Math.sin(spatialPhase - t * 2.2) * 0.38;

        const tipX = xBase + Math.sin(waveAngle) * stalkHeight;
        const tipY = groundY - Math.cos(waveAngle) * stalkHeight;
        const midX = xBase + Math.sin(waveAngle * 0.5) * (stalkHeight * 0.55);
        const midY = groundY - (stalkHeight * 0.55);

        // Tracked stalk vertical reference line (Equilibrium)
        if (isTracked) {
          ctx.beginPath();
          ctx.setLineDash([3, 3]);
          ctx.strokeStyle = 'rgba(15, 23, 42, 0.35)';
          ctx.lineWidth = 1.5;
          ctx.moveTo(xBase, groundY);
          ctx.lineTo(xBase, groundY - stalkHeight - 12);
          ctx.stroke();
          ctx.setLineDash([]);

          // Base anchor dot
          ctx.beginPath();
          ctx.arc(xBase, groundY, 4, 0, Math.PI * 2);
          ctx.fillStyle = '#0f172a';
          ctx.fill();
        }

        // Draw Stem
        ctx.beginPath();
        ctx.moveTo(xBase, groundY);
        ctx.quadraticCurveTo(midX, midY, tipX, tipY);
        ctx.strokeStyle = isTracked ? '#0f172a' : '#d97706';
        ctx.lineWidth = isTracked ? 3.5 : 2.2;
        ctx.lineCap = 'round';
        ctx.stroke();

        // Draw Wheat Ear Head
        const earAngle = waveAngle + 0.15;
        const earLen = 16;
        const earEndX = tipX + Math.sin(earAngle) * earLen;
        const earEndY = tipY - Math.cos(earAngle) * earLen;

        ctx.beginPath();
        ctx.moveTo(tipX, tipY);
        ctx.lineTo(earEndX, earEndY);
        ctx.strokeStyle = isTracked ? '#0f172a' : '#b45309';
        ctx.lineWidth = isTracked ? 5 : 4;
        ctx.stroke();

        // Draw grains
        for (let g = 1; g <= 3; g++) {
          const gx = tipX + (earEndX - tipX) * (g / 4);
          const gy = tipY + (earEndY - tipY) * (g / 4);
          
          ctx.fillStyle = isTracked ? '#0f172a' : '#f59e0b';
          ctx.beginPath();
          ctx.arc(gx + (g % 2 === 0 ? 3 : -3), gy, 2, 0, Math.PI * 2);
          ctx.fill();
        }

        // Tracked oscillation guide arrows
        if (isTracked) {
          const span = 26;
          const arrowY = groundY - stalkHeight - 8;
          ctx.beginPath();
          ctx.moveTo(xBase - span, arrowY);
          ctx.lineTo(xBase + span, arrowY);
          ctx.strokeStyle = '#0f172a';
          ctx.lineWidth = 2;
          ctx.stroke();

          // Left/Right arrow tips
          ctx.fillStyle = '#0f172a';
          // left head
          ctx.beginPath();
          ctx.moveTo(xBase - span, arrowY);
          ctx.lineTo(xBase - span + 4, arrowY - 3);
          ctx.lineTo(xBase - span + 4, arrowY + 3);
          ctx.fill();
          // right head
          ctx.beginPath();
          ctx.moveTo(xBase + span, arrowY);
          ctx.lineTo(xBase + span - 4, arrowY - 3);
          ctx.lineTo(xBase + span - 4, arrowY + 3);
          ctx.fill();
        }
      }

      if (isPlaying) {
        t += 0.024;
      }
      animId = requestAnimationFrame(draw);
    }

    function togglePlay() {
      isPlaying = !isPlaying;
      document.getElementById('toggleBtn').textContent = isPlaying ? '⏸ Pause' : '▶ Play';
    }

    // Start render loop
    draw();
  </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>Transverse Wave Characteristics</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }
    body {
      width: 100%;
      min-height: 100%;
      background: #ffffff;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      padding: 12px;
      user-select: none;
    }
    .svg-container {
      width: 100%;
      max-width: 640px;
      position: relative;
    }
    svg {
      width: 100%;
      height: auto;
      display: block;
    }
    .badge {
      fill: #eff6ff;
      stroke: #3b82f6;
      stroke-width: 1.5;
      rx: 5;
    }
    .badge-text {
      font-size: 12px;
      font-weight: 700;
      fill: #1d4ed8;
      text-anchor: middle;
      dominant-baseline: central;
    }
    .dim-label {
      font-size: 12px;
      font-weight: 700;
      text-anchor: middle;
      dominant-baseline: central;
    }
    .rest-text {
      font-size: 11px;
      font-weight: 600;
      fill: #64748b;
      text-anchor: end;
      dominant-baseline: central;
    }
    .interactive-group {
      cursor: pointer;
      transition: opacity 0.15s ease;
    }
    .interactive-group:hover {
      opacity: 0.8;
    }
  </style>
</head>
<body>

  <div class="svg-container">
    <svg viewBox="0 0 600 270" id="waveSvg">
      <defs>
        
        <marker id="arrow-blue" markerWidth="6" markerHeight="6" refX="4" refY="3" orient="auto">
          <path d="M 0,1 L 5,3 L 0,5 Z" fill="#2563eb" />
        </marker>
        <marker id="arrow-blue-rev" markerWidth="6" markerHeight="6" refX="2" refY="3" orient="auto-start-reverse">
          <path d="M 0,1 L 5,3 L 0,5 Z" fill="#2563eb" />
        </marker>
        <marker id="arrow-purple" markerWidth="6" markerHeight="6" refX="4" refY="3" orient="auto">
          <path d="M 0,1 L 5,3 L 0,5 Z" fill="#7c3aed" />
        </marker>
        <marker id="arrow-purple-rev" markerWidth="6" markerHeight="6" refX="2" refY="3" orient="auto-start-reverse">
          <path d="M 0,1 L 5,3 L 0,5 Z" fill="#7c3aed" />
        </marker>
      </defs>

      
      <line x1="30" y1="145" x2="570" y2="145" stroke="#94a3b8" stroke-width="1.5" stroke-dasharray="6,5" />
      <text x="570" y="132" class="rest-text">Rest position (equilibrium)</text>

      
      <path id="wavePath" fill="none" stroke="#0284c7" stroke-width="3" stroke-linecap="round" stroke-linejoin="round" />

      
      <line x1="120" y1="145" x2="120" y2="85" stroke="#93c5fd" stroke-width="1.2" stroke-dasharray="3,3" />

      
      <g class="interactive-group">
        <line x1="142" y1="141" x2="142" y2="89" stroke="#2563eb" stroke-width="1.75" marker-start="url(#arrow-blue-rev)" marker-end="url(#arrow-blue)" />
        <rect x="150" y="102" width="94" height="24" rx="4" fill="#ffffff" stroke="#bfdbfe" stroke-width="1" />
        <text x="197" y="114" class="dim-label" fill="#1d4ed8">Amplitude (A)</text>
      </g>

      
      <line x1="120" y1="80" x2="120" y2="24" stroke="#cbd5e1" stroke-width="1.2" stroke-dasharray="3,3" />
      <line x1="360" y1="80" x2="360" y2="24" stroke="#cbd5e1" stroke-width="1.2" stroke-dasharray="3,3" />

      
      <g class="interactive-group">
        <line x1="126" y1="32" x2="354" y2="32" stroke="#7c3aed" stroke-width="1.75" marker-start="url(#arrow-purple-rev)" marker-end="url(#arrow-purple)" />
        <rect x="193" y="20" width="94" height="24" rx="4" fill="#ffffff" stroke="#ddd6fe" stroke-width="1" />
        <text x="240" y="32" class="dim-label" fill="#6d28d9">Wavelength (λ)</text>
      </g>

      
      <g class="interactive-group">
        <circle cx="120" cy="85" r="4.5" fill="#2563eb" stroke="#ffffff" stroke-width="1.5" />
        <line x1="120" y1="81" x2="120" y2="68" stroke="#93c5fd" stroke-width="1.5" />
        <rect x="74" y="47" width="92" height="22" class="badge" />
        <text x="120" y="58" class="badge-text">Peak / Crest</text>
      </g>

      
      <circle cx="360" cy="85" r="4.5" fill="#2563eb" stroke="#ffffff" stroke-width="1.5" />

      
      <g class="interactive-group">
        <circle cx="240" cy="205" r="4.5" fill="#2563eb" stroke="#ffffff" stroke-width="1.5" />
        <line x1="240" y1="209" x2="240" y2="225" stroke="#93c5fd" stroke-width="1.5" />
        <rect x="207" y="225" width="66" height="22" class="badge" />
        <text x="240" y="236" class="badge-text">Trough</text>
      </g>
    </svg>
  </div>

  <script>
    // Mathematically plot exact 2-cycle sine wave:
    // y = y0 - A * sin(2 * pi * (x - x0) / L)
    const x0 = 60;
    const xEnd = 540;
    const y0 = 145;
    const A = 60;
    const L = 240; // 240px wavelength -> 2 cycles = 480px (x: 60 to 540)

    let d = `M ${x0} ${y0}`;
    for (let x = x0; x <= xEnd; x += 1) {
      const theta = ((x - x0) / L) * 2 * Math.PI;
      const y = y0 - A * Math.sin(theta);
      d += ` L ${x.toFixed(1)} ${y.toFixed(2)}`;
    }
    document.getElementById('wavePath').setAttribute('d', d);
  </script>
</body>
</html>

Transverse Waves: Perpendicular Oscillations

<!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;
      user-select: none;
    }

    body {
      width: 100%;
      height: 100%;
      background: #f8fafc;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      overflow: hidden;
      padding: 12px;
      color: #1e2945;
    }

    .header-labels {
      width: 100%;
      max-width: 580px;
      display: flex;
      justify-content: space-between;
      align-items: center;
      gap: 8px;
      margin-bottom: 6px;
      z-index: 10;
    }

    .badge {
      display: inline-flex;
      align-items: center;
      gap: 6px;
      padding: 6px 12px;
      border-radius: 20px;
      font-size: 13px;
      font-weight: 700;
      letter-spacing: 0.2px;
    }

    .badge-energy {
      background: #eff6ff;
      color: #2563eb;
      border: 1px solid #bfdbfe;
    }

    .badge-motion {
      background: #fef2f2;
      color: #dc2626;
      border: 1px solid #fecaca;
    }

    .canvas-container {
      position: relative;
      width: 100%;
      max-width: 580px;
      flex: 1;
      min-height: 220px;
      border-radius: 12px;
      overflow: hidden;
      background: #ffffff;
      border: 1px solid #e2e8f0;
    }

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

    .controls {
      width: 100%;
      max-width: 580px;
      display: flex;
      justify-content: center;
      align-items: center;
      gap: 12px;
      margin-top: 8px;
      z-index: 10;
    }

    .btn {
      appearance: none;
      border: 1px solid #cbd5e1;
      background: #ffffff;
      color: #334155;
      padding: 6px 14px;
      border-radius: 8px;
      font-size: 13px;
      font-weight: 600;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 6px;
      transition: background-color 0.15s, border-color 0.15s;
    }

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

    .btn:active {
      background: #e2e8f0;
    }

    .btn.active {
      background: #eff6ff;
      border-color: #3b82f6;
      color: #1d4ed8;
    }
  </style>
</head>
<body>

  <div class="header-labels">
    <div class="badge badge-energy">
      Wave Energy →
    </div>
    <div class="badge badge-motion">
      Duck Motion ↕
    </div>
  </div>

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

  <div class="controls">
    <button class="btn" id="togglePlay">⏸ Pause</button>
    <button class="btn" id="toggleSpeed">⏱ Slow Motion</button>
  </div>

  <script>
    const canvas = document.getElementById('waveCanvas');
    const container = document.getElementById('container');
    const ctx = canvas.getContext('2d');
    const togglePlayBtn = document.getElementById('togglePlay');
    const toggleSpeedBtn = document.getElementById('toggleSpeed');

    let width = 0;
    let height = 0;
    let isPlaying = true;
    let isSlow = false;
    let phase = 0;

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

    window.addEventListener('resize', resize);
    resize();

    togglePlayBtn.addEventListener('click', () => {
      isPlaying = !isPlaying;
      togglePlayBtn.textContent = isPlaying ? '⏸ Pause' : '▶ Play';
    });

    toggleSpeedBtn.addEventListener('click', () => {
      isSlow = !isSlow;
      toggleSpeedBtn.classList.toggle('active', isSlow);
      toggleSpeedBtn.textContent = isSlow ? '⚡ Normal Speed' : '⏱ Slow Motion';
    });

    function draw() {
      ctx.clearRect(0, 0, width, height);

      const midY = height * 0.52;
      const amplitude = Math.min(height * 0.18, 38);
      const wavelength = Math.min(width * 0.52, 220);
      const k = (2 * Math.PI) / wavelength;
      const centerX = width * 0.5;

      // 1. Reference Grid Lines & 90-degree Perpendicular Marker
      const duckY = midY - amplitude * Math.sin(k * centerX - phase);

      // Red vertical guideline
      ctx.save();
      ctx.setLineDash([5, 5]);
      ctx.strokeStyle = '#ef4444';
      ctx.lineWidth = 2;
      ctx.beginPath();
      ctx.moveTo(centerX, 20);
      ctx.lineTo(centerX, height - 20);
      ctx.stroke();
      ctx.restore();

      // Top and Bottom oscillation limit ticks
      ctx.strokeStyle = 'rgba(239, 68, 68, 0.4)';
      ctx.lineWidth = 1.5;
      ctx.beginPath();
      ctx.moveTo(centerX - 18, midY - amplitude);
      ctx.lineTo(centerX + 18, midY - amplitude);
      ctx.moveTo(centerX - 18, midY + amplitude);
      ctx.lineTo(centerX + 18, midY + amplitude);
      ctx.stroke();

      // Perpendicular 90° symbol at wave center
      ctx.strokeStyle = '#94a3b8';
      ctx.lineWidth = 1.5;
      ctx.strokeRect(centerX, midY - 14, 14, 14);

      // 2. Wave Surface & Body of Water
      ctx.beginPath();
      ctx.moveTo(0, height);
      for (let x = 0; x <= width; x += 3) {
        const y = midY - amplitude * Math.sin(k * x - phase);
        ctx.lineTo(x, y);
      }
      ctx.lineTo(width, height);
      ctx.closePath();

      const waterGradient = ctx.createLinearGradient(0, midY - amplitude, 0, height);
      waterGradient.addColorStop(0, 'rgba(56, 189, 248, 0.45)');
      waterGradient.addColorStop(0.3, 'rgba(14, 165, 233, 0.65)');
      waterGradient.addColorStop(1, 'rgba(2, 132, 199, 0.9)');
      ctx.fillStyle = waterGradient;
      ctx.fill();

      // Wave crest stroke
      ctx.beginPath();
      for (let x = 0; x <= width; x += 3) {
        const y = midY - amplitude * Math.sin(k * x - phase);
        if (x === 0) ctx.moveTo(x, y);
        else ctx.lineTo(x, y);
      }
      ctx.strokeStyle = '#0284c7';
      ctx.lineWidth = 3;
      ctx.stroke();

      // Wave travel directional indicator arrows in the water
      const arrowY = height - 26;
      ctx.fillStyle = '#0369a1';
      ctx.strokeStyle = '#0369a1';
      ctx.lineWidth = 2;
      ctx.beginPath();
      ctx.moveTo(width * 0.15, arrowY);
      ctx.lineTo(width * 0.35, arrowY);
      ctx.stroke();
      ctx.beginPath();
      ctx.moveTo(width * 0.35 - 6, arrowY - 4);
      ctx.lineTo(width * 0.35, arrowY);
      ctx.lineTo(width * 0.35 - 6, arrowY + 4);
      ctx.stroke();

      ctx.beginPath();
      ctx.moveTo(width * 0.65, arrowY);
      ctx.lineTo(width * 0.85, arrowY);
      ctx.stroke();
      ctx.beginPath();
      ctx.moveTo(width * 0.85 - 6, arrowY - 4);
      ctx.lineTo(width * 0.85, arrowY);
      ctx.lineTo(width * 0.85 - 6, arrowY + 4);
      ctx.stroke();

      // 3. Yellow Rubber Duck
      const slope = -amplitude * k * Math.cos(k * centerX - phase);
      const angle = Math.atan(slope) * 0.5; // slight tilt following water angle

      ctx.save();
      ctx.translate(centerX, duckY);
      ctx.rotate(angle);

      // Duck Emoji rendered sharp & centered
      ctx.font = '38px sans-serif';
      ctx.textAlign = 'center';
      ctx.textBaseline = 'middle';
      ctx.fillText('🦆', 0, -10);
      ctx.restore();

      // Reference dot firmly tracking center
      ctx.fillStyle = '#dc2626';
      ctx.beginPath();
      ctx.arc(centerX, duckY, 4, 0, Math.PI * 2);
      ctx.fill();

      // 4. Motion arrows along vertical guideline
      const arrowOffset = 34;
      ctx.fillStyle = '#dc2626';
      ctx.strokeStyle = '#dc2626';
      ctx.lineWidth = 2;

      // Up arrow
      ctx.beginPath();
      ctx.moveTo(centerX - arrowOffset, midY - 6);
      ctx.lineTo(centerX - arrowOffset, midY - 26);
      ctx.stroke();
      ctx.beginPath();
      ctx.moveTo(centerX - arrowOffset - 4, midY - 20);
      ctx.lineTo(centerX - arrowOffset, midY - 26);
      ctx.lineTo(centerX - arrowOffset + 4, midY - 20);
      ctx.stroke();

      // Down arrow
      ctx.beginPath();
      ctx.moveTo(centerX - arrowOffset, midY + 6);
      ctx.lineTo(centerX - arrowOffset, midY + 26);
      ctx.stroke();
      ctx.beginPath();
      ctx.moveTo(centerX - arrowOffset - 4, midY + 20);
      ctx.lineTo(centerX - arrowOffset, midY + 26);
      ctx.lineTo(centerX - arrowOffset + 4, midY + 20);
      ctx.stroke();

      // Update Phase
      if (isPlaying) {
        const speed = isSlow ? 0.015 : 0.045;
        phase += speed;
      }

      requestAnimationFrame(draw);
    }

    requestAnimationFrame(draw);
  </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>Transverse Waves Comparison</title>
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      width: 100%;
      min-height: 100%;
      font-family: system-ui, -apple-system, sans-serif;
      background: #ffffff;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      padding: 10px;
      gap: 10px;
    }

    .shared-rule {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      background: #f0f7ff;
      border: 1px solid #bae0ff;
      border-radius: 20px;
      padding: 6px 14px;
      font-size: 13px;
      font-weight: 700;
      color: #0066cc;
    }

    .cards-grid {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 10px;
      width: 100%;
      max-width: 660px;
    }

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

    .wave-card {
      background: #fafbfc;
      border: 1px solid #e2e8f0;
      border-radius: 12px;
      padding: 10px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 8px;
    }

    .card-title {
      font-size: 14px;
      font-weight: 700;
      color: #1e2945;
      display: flex;
      align-items: center;
      gap: 6px;
    }

    .canvas-container {
      width: 100%;
      height: 130px;
      position: relative;
      background: #ffffff;
      border-radius: 8px;
      border: 1px solid #edf2f7;
      overflow: hidden;
    }

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

    .badge {
      font-size: 12px;
      font-weight: 600;
      padding: 4px 10px;
      border-radius: 6px;
      text-align: center;
    }

    .badge-mech {
      background: #e6f4ea;
      color: #137333;
      border: 1px solid #ceead6;
    }

    .badge-em {
      background: #fef7e0;
      color: #b06000;
      border: 1px solid #feefc3;
    }

    .legend {
      display: flex;
      justify-content: space-between;
      width: 100%;
      font-size: 11px;
      font-weight: 600;
      color: #64748b;
      padding: 0 4px;
    }
  </style>
</head>
<body>

  <div class="shared-rule">
    <span>Oscillations ⟂ Energy (90°)</span>
  </div>

  <div class="cards-grid">
    
    <div class="wave-card">
      <div class="card-title">Mechanical</div>
      <div class="canvas-container">
        <canvas id="mechCanvas"></canvas>
      </div>
      <div class="legend">
        <span>↕ Vibration</span>
        <span>Energy →</span>
      </div>
      <div class="badge badge-mech">Medium required</div>
    </div>

    
    <div class="wave-card">
      <div class="card-title">Electromagnetic</div>
      <div class="canvas-container">
        <canvas id="emCanvas"></canvas>
      </div>
      <div class="legend">
        <span>↕ E &nbsp; ⤢ B</span>
        <span>Energy →</span>
      </div>
      <div class="badge badge-em">Vacuum (No medium)</div>
    </div>
  </div>

  <script>
    const mechCanvas = document.getElementById('mechCanvas');
    const emCanvas = document.getElementById('emCanvas');
    const ctxMech = mechCanvas.getContext('2d');
    const ctxEm = emCanvas.getContext('2d');

    let t = 0;

    function resize() {
      const dpr = window.devicePixelRatio || 1;
      [mechCanvas, emCanvas].forEach(c => {
        const rect = c.getBoundingClientRect();
        c.width = rect.width * dpr;
        c.height = rect.height * dpr;
      });
    }

    window.addEventListener('resize', resize);
    resize();

    function drawArrow(ctx, x1, y1, x2, y2, color, headSize = 6) {
      ctx.strokeStyle = color;
      ctx.fillStyle = color;
      ctx.lineWidth = 1.5;
      ctx.beginPath();
      ctx.moveTo(x1, y1);
      ctx.lineTo(x2, y2);
      ctx.stroke();

      const angle = Math.atan2(y2 - y1, x2 - x1);
      ctx.beginPath();
      ctx.moveTo(x2, y2);
      ctx.lineTo(x2 - headSize * Math.cos(angle - Math.PI / 6), y2 - headSize * Math.sin(angle - Math.PI / 6));
      ctx.lineTo(x2 - headSize * Math.cos(angle + Math.PI / 6), y2 - headSize * Math.sin(angle + Math.PI / 6));
      ctx.closePath();
      ctx.fill();
    }

    function render() {
      t += 0.04;
      const dpr = window.devicePixelRatio || 1;

      // 1. Render Mechanical Wave
      const wM = mechCanvas.width;
      const hM = mechCanvas.height;
      ctxMech.setTransform(1, 0, 0, 1, 0, 0);
      ctxMech.clearRect(0, 0, wM, hM);
      ctxMech.scale(dpr, dpr);

      const widthM = wM / dpr;
      const heightM = hM / dpr;
      const midYM = heightM / 2 + 5;
      const ampM = heightM * 0.28;
      const kM = (Math.PI * 2) / (widthM * 0.7);

      // Draw dashed reference line & energy arrow
      ctxMech.strokeStyle = '#e2e8f0';
      ctxMech.lineWidth = 1;
      ctxMech.setLineDash([4, 4]);
      ctxMech.beginPath();
      ctxMech.moveTo(10, midYM);
      ctxMech.lineTo(widthM - 10, midYM);
      ctxMech.stroke();
      ctxMech.setLineDash([]);

      drawArrow(ctxMech, 20, 16, widthM - 20, 16, '#0284c7', 5);

      // Draw continuous rope line
      ctxMech.strokeStyle = '#94a3b8';
      ctxMech.lineWidth = 2;
      ctxMech.beginPath();
      for (let x = 10; x <= widthM - 10; x += 2) {
        const y = midYM + Math.sin(x * kM - t) * ampM;
        if (x === 10) ctxMech.moveTo(x, y);
        else ctxMech.lineTo(x, y);
      }
      ctxMech.stroke();

      // Draw discrete vibrating particles
      const numParticles = 9;
      for (let i = 0; i < numParticles; i++) {
        const px = 20 + i * ((widthM - 40) / (numParticles - 1));
        const py = midYM + Math.sin(px * kM - t) * ampM;

        // Particle vertical track guide
        if (i === 2 || i === 6) {
          ctxMech.strokeStyle = '#cbd5e1';
          ctxMech.lineWidth = 1;
          ctxMech.setLineDash([2, 2]);
          ctxMech.beginPath();
          ctxMech.moveTo(px, midYM - ampM - 4);
          ctxMech.lineTo(px, midYM + ampM + 4);
          ctxMech.stroke();
          ctxMech.setLineDash([]);

          // Motion vector indicator on highlighted particles
          const vel = -Math.cos(px * kM - t);
          drawArrow(ctxMech, px, py, px, py + vel * 12, '#16a34a', 4);
        }

        // Particle bead
        ctxMech.fillStyle = (i === 2 || i === 6) ? '#16a34a' : '#0284c7';
        ctxMech.beginPath();
        ctxMech.arc(px, py, (i === 2 || i === 6) ? 5 : 3.5, 0, Math.PI * 2);
        ctxMech.fill();
        ctxMech.strokeStyle = '#ffffff';
        ctxMech.lineWidth = 1.5;
        ctxMech.stroke();
      }

      // 2. Render EM Wave (E-field in Y, B-field in Z-perspective)
      const wE = emCanvas.width;
      const hE = emCanvas.height;
      ctxEm.setTransform(1, 0, 0, 1, 0, 0);
      ctxEm.clearRect(0, 0, wE, hE);
      ctxEm.scale(dpr, dpr);

      const widthE = wE / dpr;
      const heightE = hE / dpr;
      const midYE = heightE / 2 + 5;
      const ampE = heightE * 0.28;
      const kE = (Math.PI * 2) / (widthE * 0.7);

      // Central axis
      ctxEm.strokeStyle = '#cbd5e1';
      ctxEm.lineWidth = 1;
      ctxEm.beginPath();
      ctxEm.moveTo(10, midYE);
      ctxEm.lineTo(widthE - 10, midYE);
      ctxEm.stroke();

      drawArrow(ctxEm, 20, 16, widthE - 20, 16, '#0284c7', 5);

      // Draw oscillating field vectors (E = blue vertical, B = orange perspective)
      const step = (widthE - 40) / 14;
      for (let x = 20; x <= widthE - 20; x += step) {
        const val = Math.sin(x * kE - t);

        // B-field (isometric perspective: dx, dy)
        const bLen = val * ampE * 0.7;
        const bX = x - bLen * 0.6;
        const bY = midYE + bLen * 0.35;
        ctxEm.strokeStyle = '#ea580c';
        ctxEm.lineWidth = 1.5;
        ctxEm.beginPath();
        ctxEm.moveTo(x, midYE);
        ctxEm.lineTo(bX, bY);
        ctxEm.stroke();

        // E-field (vertical)
        const eY = midYE - val * ampE;
        ctxEm.strokeStyle = '#2563eb';
        ctxEm.lineWidth = 1.5;
        ctxEm.beginPath();
        ctxEm.moveTo(x, midYE);
        ctxEm.lineTo(x, eY);
        ctxEm.stroke();
      }

      // Continuous E-field envelope line
      ctxEm.strokeStyle = '#2563eb';
      ctxEm.lineWidth = 1.5;
      ctxEm.beginPath();
      for (let x = 10; x <= widthE - 10; x += 2) {
        const y = midYE - Math.sin(x * kE - t) * ampE;
        if (x === 10) ctxEm.moveTo(x, y);
        else ctxEm.lineTo(x, y);
      }
      ctxEm.stroke();

      // Continuous B-field envelope line
      ctxEm.strokeStyle = '#ea580c';
      ctxEm.lineWidth = 1.5;
      ctxEm.beginPath();
      for (let x = 10; x <= widthE - 10; x += 2) {
        const bLen = Math.sin(x * kE - t) * ampE * 0.7;
        const bX = x - bLen * 0.6;
        const bY = midYE + bLen * 0.35;
        if (x === 10) ctxEm.moveTo(bX, bY);
        else ctxEm.lineTo(bX, bY);
      }
      ctxEm.stroke();

      requestAnimationFrame(render);
    }

    requestAnimationFrame(render);
  </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>Transverse Wave: Perpendicular Oscillations</title>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }
    body {
      width: 100%;
      height: 100%;
      background-color: #f8f9fa;
      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;
      user-select: none;
      overflow: hidden;
    }
    .top-bar {
      width: 100%;
      max-width: 580px;
      display: flex;
      justify-content: space-between;
      align-items: center;
      margin-bottom: 4px;
    }
    .title-badge {
      font-size: 13px;
      font-weight: 700;
      text-transform: uppercase;
      letter-spacing: 0.5px;
      color: #4b5563;
    }
    .btn {
      display: inline-flex;
      align-items: center;
      gap: 6px;
      background: #ffffff;
      border: 1px solid #d1d5db;
      border-radius: 6px;
      padding: 5px 12px;
      font-size: 13px;
      font-weight: 600;
      color: #1e2945;
      cursor: pointer;
      box-shadow: 0 1px 2px rgba(0,0,0,0.05);
      transition: background-color 0.15s, border-color 0.15s;
    }
    .btn:hover {
      background: #f3f4f6;
      border-color: #9ca3af;
    }
    .btn:active {
      background: #e5e7eb;
    }
    .svg-container {
      width: 100%;
      max-width: 580px;
      flex-grow: 1;
      display: flex;
      align-items: center;
      justify-content: center;
    }
    svg {
      width: 100%;
      height: auto;
      display: block;
      overflow: visible;
    }
    .wave-line {
      fill: none;
      stroke: #0284c7;
      stroke-width: 4;
      stroke-linecap: round;
      stroke-linejoin: round;
    }
    .equilibrium-line {
      stroke: #cbd5e1;
      stroke-width: 1.5;
      stroke-dasharray: 5 4;
    }
    .guide-line {
      stroke: #ef4444;
      stroke-width: 1.5;
      stroke-dasharray: 4 4;
      opacity: 0.7;
    }
    .marker-dot {
      fill: #ef4444;
      stroke: #ffffff;
      stroke-width: 2.5;
      filter: drop-shadow(0 0 6px rgba(239, 68, 68, 0.8));
    }
    .arrow-energy {
      stroke: #ea580c;
      stroke-width: 3.5;
      stroke-linecap: round;
    }
    .arrow-oscillation {
      stroke: #2563eb;
      stroke-width: 3.5;
      stroke-linecap: round;
    }
    .label-energy {
      fill: #ea580c;
      font-size: 13px;
      font-weight: 700;
    }
    .label-oscillation {
      fill: #2563eb;
      font-size: 13px;
      font-weight: 700;
    }
    .angle-marker {
      fill: none;
      stroke: #1e2945;
      stroke-width: 2;
    }
    .angle-label {
      fill: #1e2945;
      font-size: 13px;
      font-weight: 800;
    }
    .particle-label {
      fill: #ef4444;
      font-size: 12px;
      font-weight: 700;
    }
  </style>
</head>
<body>

  <div class="top-bar">
    <div class="title-badge">Transverse Wave</div>
    <button id="playBtn" class="btn" aria-label="Toggle animation">
      <span id="playIcon">⏸</span>
      <span id="playText">Pause</span>
    </button>
  </div>

  <div class="svg-container">
    <svg viewBox="0 0 560 360" preserveAspectRatio="xMidYMid meet">
      <defs>
        
        <marker id="arrow-orange" markerWidth="8" markerHeight="8" refX="6" refY="4" orient="auto">
          <path d="M 0 0 L 8 4 L 0 8 Z" fill="#ea580c" />
        </marker>
        <marker id="arrow-blue-up" markerWidth="8" markerHeight="8" refX="4" refY="2" orient="auto">
          <path d="M 0 6 L 4 0 L 8 6 Z" fill="#2563eb" />
        </marker>
        <marker id="arrow-blue-down" markerWidth="8" markerHeight="8" refX="4" refY="6" orient="auto">
          <path d="M 0 2 L 4 8 L 8 2 Z" fill="#2563eb" />
        </marker>
      </defs>

      
      <line x1="20" y1="130" x2="540" y2="130" class="equilibrium-line" />
      <text x="24" y="122" fill="#94a3b8" font-size="11" font-weight="600">Rest Position</text>

      
      <line x1="190" y1="50" x2="190" y2="210" class="guide-line" />

      
      <path id="wavePath" class="wave-line" d="" />

      
      <circle id="particle" cx="190" cy="130" r="7.5" class="marker-dot" />
      <text id="particleText" x="204" y="134" class="particle-label">Particle</text>

      
      <g transform="translate(190, 275)">
        
        <path d="M 0,-18 L 18,-18 L 18,0" class="angle-marker" />
        <circle cx="9" cy="-9" r="2" fill="#1e2945" />
        <text x="24" y="-22" class="angle-label">90°</text>

        
        <line x1="0" y1="48" x2="0" y2="-48" class="arrow-oscillation" />
        <path d="M -5,-42 L 0,-52 L 5,-42 Z" fill="#2563eb" />
        <path d="M -5,42 L 0,52 L 5,42 Z" fill="#2563eb" />
        <text x="-12" y="4" class="label-oscillation" text-anchor="end">Direction of<tspan x="-12" dy="16">Oscillation</tspan></text>

        
        <line x1="0" y1="0" x2="175" y2="0" class="arrow-energy" marker-end="url(#arrow-orange)" />
        <text x="90" y="22" class="label-energy">Direction of Energy Transfer</text>
      </g>
    </svg>
  </div>

  <script>
    const wavePath = document.getElementById('wavePath');
    const particle = document.getElementById('particle');
    const particleText = document.getElementById('particleText');
    const playBtn = document.getElementById('playBtn');
    const playIcon = document.getElementById('playIcon');
    const playText = document.getElementById('playText');

    let isPlaying = true;
    let phase = 0;
    let lastTime = performance.now();

    const amplitude = 52;
    const centerY = 130;
    const wavelength = 220;
    const k = (2 * Math.PI) / wavelength;
    const speed = 0.18; // phase speed in rad/ms
    const particleX = 190;
    const xStart = 20;
    const xEnd = 540;
    const step = 4;

    function render(currentPhase) {
      let d = `M ${xStart} ${centerY + amplitude * Math.sin(k * xStart - currentPhase)}`;
      for (let x = xStart + step; x <= xEnd; x += step) {
        const y = centerY + amplitude * Math.sin(k * x - currentPhase);
        d += ` L ${x.toFixed(1)} ${y.toFixed(1)}`;
      }
      wavePath.setAttribute('d', d);

      // Update vertical oscillating particle
      const particleY = centerY + amplitude * Math.sin(k * particleX - currentPhase);
      particle.setAttribute('cy', particleY.toFixed(1));
      particleText.setAttribute('y', (particleY + 4).toFixed(1));
    }

    function animate(now) {
      if (isPlaying) {
        const delta = Math.min(now - lastTime, 50);
        phase += (speed * delta) * 0.02;
        render(phase);
      }
      lastTime = now;
      requestAnimationFrame(animate);
    }

    playBtn.addEventListener('click', () => {
      isPlaying = !isPlaying;
      if (isPlaying) {
        playIcon.textContent = '⏸';
        playText.textContent = 'Pause';
      } else {
        playIcon.textContent = '▶';
        playText.textContent = 'Play';
      }
    });

    // Initial render and start loop
    render(0);
    requestAnimationFrame(animate);
  </script>
</body>
</html>

UK-GCSE-SCIENCE-PHYS-WAV

Child standards (2)

Aligned learning resources

Related diagrams