<!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">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    }

    body {
      background: #f8fafc;
      color: #1e2945;
      padding: 12px;
      display: flex;
      flex-direction: column;
      gap: 12px;
      min-height: 100%;
    }

    /* Wave Tank Display */
    .tank-view {
      position: relative;
      background: #ffffff;
      border: 2px solid #0284c7;
      border-radius: 12px;
      height: 140px;
      overflow: hidden;
      display: flex;
      align-items: center;
      justify-content: center;
    }

    .tank-svg {
      width: 100%;
      height: 100%;
      display: block;
    }

    /* Reference Marker */
    .marker-line {
      position: absolute;
      top: 0;
      bottom: 0;
      left: 50%;
      width: 3px;
      background: #ef4444;
      transform: translateX(-50%);
      z-index: 5;
    }

    .marker-tag {
      position: absolute;
      top: 6px;
      left: 50%;
      transform: translateX(-50%);
      background: #ef4444;
      color: #ffffff;
      font-size: 11px;
      font-weight: 700;
      padding: 2px 8px;
      border-radius: 4px;
      text-transform: uppercase;
      letter-spacing: 0.5px;
      z-index: 6;
      white-space: nowrap;
    }

    .counter-badge {
      position: absolute;
      bottom: 8px;
      left: 50%;
      transform: translateX(-50%);
      background: rgba(15, 23, 42, 0.85);
      color: #38bdf8;
      font-size: 12px;
      font-weight: 700;
      padding: 3px 10px;
      border-radius: 20px;
      border: 1px solid #0284c7;
      z-index: 6;
      white-space: nowrap;
    }

    /* Bottom Cards Grid */
    .cards-row {
      display: grid;
      grid-template-columns: 1fr 1.3fr;
      gap: 12px;
    }

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

    .info-card {
      background: #ffffff;
      border: 1.5px solid #0284c7;
      border-radius: 10px;
      padding: 12px 14px;
      display: flex;
      flex-direction: column;
      justify-content: center;
      position: relative;
    }

    /* Stopwatch Card */
    .stopwatch-card {
      align-items: center;
      text-align: center;
      gap: 4px;
    }

    .card-label {
      font-size: 11px;
      font-weight: 700;
      color: #64748b;
      text-transform: uppercase;
      letter-spacing: 0.5px;
    }

    .digital-clock {
      font-family: ui-monospace, 'SF Mono', Menlo, Consolas, monospace;
      font-size: 32px;
      font-weight: 800;
      color: #0f172a;
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      padding: 4px 14px;
      border-radius: 6px;
      letter-spacing: 1px;
      min-width: 130px;
    }

    /* Calculation Card */
    .calc-card {
      gap: 6px;
    }

    .formula-row {
      font-size: 13px;
      font-weight: 700;
      color: #0369a1;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      background: #f0f9ff;
      padding: 4px 8px;
      border-radius: 6px;
    }

    .math-row {
      font-size: 15px;
      font-weight: 800;
      color: #0f172a;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 4px;
      flex-wrap: wrap;
    }

    .fraction {
      display: inline-flex;
      flex-direction: column;
      vertical-align: middle;
      text-align: center;
      padding: 0 4px;
      font-size: 13px;
      line-height: 1.1;
    }

    .fraction-top {
      border-bottom: 1.5px solid #0f172a;
      padding-bottom: 1px;
    }

    .fraction-bottom {
      padding-top: 1px;
    }

    .result-badge {
      color: #0284c7;
      background: #e0f2fe;
      padding: 2px 8px;
      border-radius: 6px;
      font-size: 16px;
      font-weight: 800;
    }

    /* Control Bar */
    .controls {
      display: flex;
      justify-content: center;
      gap: 8px;
    }

    .btn {
      background: #0284c7;
      color: #ffffff;
      border: none;
      border-radius: 6px;
      padding: 6px 16px;
      font-size: 13px;
      font-weight: 700;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 6px;
    }

    .btn-secondary {
      background: #e2e8f0;
      color: #334155;
    }
  </style>
</head>
<body>

  
  <div class="tank-view">
    <div class="marker-tag">Marker</div>
    <div class="marker-line"></div>
    <div id="crestCount" class="counter-badge">Waves: 12 / 12</div>

    <svg class="tank-svg" viewBox="0 0 700 140" preserveAspectRatio="none">
      <defs>
        <linearGradient id="waterGrad" x1="0" y1="0" x2="0" y2="1">
          <stop offset="0%" stop-color="#38bdf8" stop-opacity="0.45"/>
          <stop offset="100%" stop-color="#0284c7" stop-opacity="0.85"/>
        </linearGradient>
      </defs>
      
      <path id="waveArea" fill="url(#waterGrad)" d=""/>
      
      <path id="waveStroke" fill="none" stroke="#0284c7" stroke-width="3.5" d=""/>
      
      <g id="crestDots"></g>
    </svg>
  </div>

  
  <div class="cards-row">
    
    <div class="info-card stopwatch-card">
      <span class="card-label">Time (t)</span>
      <div id="timerDisplay" class="digital-clock">10.0 s</div>
    </div>

    
    <div class="info-card calc-card">
      <div class="formula-row">
        <span>Frequency (f) =</span>
        <div class="fraction">
          <span class="fraction-top">Total Waves</span>
          <span class="fraction-bottom">Time</span>
        </div>
      </div>
      <div class="math-row">
        <span>f =</span>
        <div class="fraction">
          <span id="mathWaves" class="fraction-top">12 waves</span>
          <span id="mathTime" class="fraction-bottom">10.0 s</span>
        </div>
        <span>=</span>
        <span id="mathResult" class="result-badge">1.2 Hz</span>
      </div>
    </div>
  </div>

  
  <div class="controls">
    <button id="playBtn" class="btn" onclick="togglePlay()">
      <span id="playIcon">⏸</span> <span id="playText">Pause</span>
    </button>
    <button class="btn btn-secondary" onclick="resetSim()">↺ Reset</button>
  </div>

  <script>
    const TOTAL_WAVES = 12;
    const TOTAL_TIME = 10.0;
    const WAVELENGTH = 50; // pixels per cycle
    const SPEED = (TOTAL_WAVES * WAVELENGTH) / TOTAL_TIME; // px per second = 60 px/s

    let isPlaying = true;
    let currentTime = 10.0;
    let lastTimestamp = null;

    const waveArea = document.getElementById('waveArea');
    const waveStroke = document.getElementById('waveStroke');
    const crestDots = document.getElementById('crestDots');
    const timerDisplay = document.getElementById('timerDisplay');
    const crestCount = document.getElementById('crestCount');
    const mathWaves = document.getElementById('mathWaves');
    const mathTime = document.getElementById('mathTime');
    const mathResult = document.getElementById('mathResult');
    const playIcon = document.getElementById('playIcon');
    const playText = document.getElementById('playText');

    function renderWave(time) {
      const width = 700;
      const height = 140;
      const baseline = 75;
      const amplitude = 28;
      
      const offset = (time * SPEED) % WAVELENGTH;
      const totalShift = time * SPEED;

      // Build sine path
      let d = `M 0 ${baseline}`;
      let dotsHtml = '';

      for (let x = 0; x <= width; x += 4) {
        const y = baseline + amplitude * Math.sin(((x - totalShift) / WAVELENGTH) * 2 * Math.PI - Math.PI / 2);
        d += ` L ${x} ${y.toFixed(1)}`;
      }

      // Stroke and Fill
      waveStroke.setAttribute('d', d);
      waveArea.setAttribute('d', d + ` L ${width} ${height} L 0 ${height} Z`);

      // Calculate waves that have crossed center marker (x = 350)
      const markerX = 350;
      // At t=0, crest 0 is at x = markerX
      const crossed = Math.min(TOTAL_WAVES, Math.floor(totalShift / WAVELENGTH));

      // Draw active crest dots along wave
      const startCrestIndex = Math.floor((0 - totalShift) / WAVELENGTH);
      const endCrestIndex = Math.ceil((width - totalShift) / WAVELENGTH);

      for (let i = startCrestIndex; i <= endCrestIndex; i++) {
        const cx = i * WAVELENGTH + totalShift;
        const cy = baseline - amplitude;
        const isPastMarker = cx >= markerX;
        const color = isPastMarker ? '#0284c7' : '#94a3b8';
        
        dotsHtml += `<circle cx="${cx.toFixed(1)}" cy="${cy.toFixed(1)}" r="4.5" fill="${color}" stroke="#ffffff" stroke-width="1.5" />`;
      }
      crestDots.innerHTML = dotsHtml;

      // Update Displays
      timerDisplay.textContent = time.toFixed(1) + ' s';
      crestCount.textContent = `Waves: ${crossed} / ${TOTAL_WAVES}`;
      
      mathWaves.textContent = `${crossed} waves`;
      mathTime.textContent = `${Math.max(0.1, time).toFixed(1)} s`;
      
      const freq = time > 0 ? (crossed / time).toFixed(2) : '0.00';
      mathResult.textContent = (time >= TOTAL_TIME) ? '1.2 Hz' : `${freq} Hz`;
    }

    function animate(timestamp) {
      if (!lastTimestamp) lastTimestamp = timestamp;
      const dt = (timestamp - lastTimestamp) / 1000;
      lastTimestamp = timestamp;

      if (isPlaying) {
        currentTime += dt;
        if (currentTime > TOTAL_TIME + 1.5) {
          currentTime = 0; // loop cleanly
        }
        renderWave(Math.min(TOTAL_TIME, currentTime));
      }

      requestAnimationFrame(animate);
    }

    function togglePlay() {
      isPlaying = !isPlaying;
      playIcon.textContent = isPlaying ? '⏸' : '▶';
      playText.textContent = isPlaying ? 'Pause' : 'Play';
    }

    function resetSim() {
      currentTime = 0;
      renderWave(0);
    }

    // Initial Render
    renderWave(TOTAL_TIME);
    requestAnimationFrame(animate);
  </script>
</body>
</html>

Required Practical: Measuring Wave Speed in a Ripple Tank

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

    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      color: #1e2945;
      background: transparent;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      padding: 8px 12px;
      min-height: 100vh;
      user-select: none;
    }

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

    .diagram-svg {
      width: 100%;
      height: auto;
      display: block;
      max-height: 310px;
    }

    .interactive-row {
      display: flex;
      gap: 8px;
      margin-top: 2px;
      flex-wrap: wrap;
      justify-content: center;
      width: 100%;
    }

    .btn {
      background: #f1f5f9;
      border: 1.5px solid #cbd5e1;
      color: #1e2945;
      padding: 7px 14px;
      border-radius: 6px;
      font-size: 13px;
      font-weight: 600;
      cursor: pointer;
      transition: background 0.2s, border-color 0.2s, color 0.2s;
    }

    .btn:hover {
      background: #e2e8f0;
    }

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

    .calc-card {
      width: 100%;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 8px;
      padding: 10px 14px;
      display: flex;
      flex-direction: column;
      gap: 6px;
      text-align: center;
    }

    .formula-line {
      font-size: 15px;
      font-weight: 600;
      color: #0f172a;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      flex-wrap: wrap;
      line-height: 1.4;
    }

    .highlight-badge {
      background: #e0f2fe;
      color: #0369a1;
      padding: 2px 8px;
      border-radius: 6px;
      font-weight: 700;
      display: inline-block;
    }

    .note-text {
      font-size: 12.5px;
      color: #475569;
      line-height: 1.35;
    }

    .crest-elem, .gap-elem {
      transition: opacity 0.25s ease;
    }

    @media (max-width: 420px) {
      .btn {
        font-size: 12px;
        padding: 6px 10px;
        flex: 1 1 calc(50% - 8px);
        text-align: center;
      }
      .formula-line {
        font-size: 13.5px;
        gap: 4px;
      }
      .note-text {
        font-size: 11.5px;
      }
      .calc-card {
        padding: 8px 10px;
      }
    }
  </style>
</head>
<body>

  <div class="container">
    
    <svg class="diagram-svg" viewBox="0 0 600 230" aria-label="Ripple tank wavelength measurement diagram">
      <defs>
        
        <linearGradient id="crestGrad" x1="0%" y1="0%" x2="100%" y2="0%">
          <stop offset="0%" stop-color="#38bdf8" stop-opacity="0.15" />
          <stop offset="45%" stop-color="#0284c7" stop-opacity="0.85" />
          <stop offset="50%" stop-color="#0369a1" stop-opacity="1" />
          <stop offset="55%" stop-color="#0284c7" stop-opacity="0.85" />
          <stop offset="100%" stop-color="#38bdf8" stop-opacity="0.15" />
        </linearGradient>

        
        <marker id="arrowL" viewBox="0 0 10 10" refX="2" refY="5" markerWidth="6" markerHeight="6" orient="auto-start-reverse">
          <path d="M 10 1.5 L 2 5 L 10 8.5 z" fill="#0369a1" />
        </marker>
        <marker id="arrowR" viewBox="0 0 10 10" refX="8" refY="5" markerWidth="6" markerHeight="6" orient="auto">
          <path d="M 0 1.5 L 8 5 L 0 8.5 z" fill="#0369a1" />
        </marker>

        <marker id="subArrowL" viewBox="0 0 10 10" refX="2" refY="5" markerWidth="5" markerHeight="5" orient="auto-start-reverse">
          <path d="M 10 2 L 2 5 L 10 8 z" fill="#0284c7" />
        </marker>
        <marker id="subArrowR" viewBox="0 0 10 10" refX="8" refY="5" markerWidth="5" markerHeight="5" orient="auto">
          <path d="M 0 2 L 8 5 L 0 8 z" fill="#0284c7" />
        </marker>
      </defs>

      
      <rect x="18" y="6" width="564" height="92" rx="8" fill="#f8fafc" stroke="#cbd5e1" stroke-width="1.5" />
      <text x="30" y="23" font-size="11" font-weight="700" fill="#64748b" letter-spacing="0.5">SCREEN SHADOW PATTERN</text>

      
      
      <g class="crest-elem" id="crest-1">
        <rect x="46" y="8" width="28" height="88" fill="url(#crestGrad)" rx="3" />
        <line x1="60" y1="8" x2="60" y2="96" stroke="#0284c7" stroke-width="2" />
        <circle cx="60" cy="38" r="8" fill="#0369a1" />
        <text x="60" y="42" font-size="11" font-weight="700" fill="#ffffff" text-anchor="middle">1</text>
      </g>

      
      <g class="crest-elem" id="crest-2">
        <rect x="136" y="8" width="28" height="88" fill="url(#crestGrad)" rx="3" />
        <line x1="150" y1="8" x2="150" y2="96" stroke="#0284c7" stroke-width="2" />
        <circle cx="150" cy="38" r="8" fill="#0369a1" />
        <text x="150" y="42" font-size="11" font-weight="700" fill="#ffffff" text-anchor="middle">2</text>
      </g>

      
      <g class="crest-elem" id="crest-3">
        <rect x="226" y="8" width="28" height="88" fill="url(#crestGrad)" rx="3" />
        <line x1="240" y1="8" x2="240" y2="96" stroke="#0284c7" stroke-width="2" />
        <circle cx="240" cy="38" r="8" fill="#0369a1" />
        <text x="240" y="42" font-size="11" font-weight="700" fill="#ffffff" text-anchor="middle">3</text>
      </g>

      
      <g class="crest-elem" id="crest-4">
        <rect x="316" y="8" width="28" height="88" fill="url(#crestGrad)" rx="3" />
        <line x1="330" y1="8" x2="330" y2="96" stroke="#0284c7" stroke-width="2" />
        <circle cx="330" cy="38" r="8" fill="#0369a1" />
        <text x="330" y="42" font-size="11" font-weight="700" fill="#ffffff" text-anchor="middle">4</text>
      </g>

      
      <g class="crest-elem" id="crest-5">
        <rect x="406" y="8" width="28" height="88" fill="url(#crestGrad)" rx="3" />
        <line x1="420" y1="8" x2="420" y2="96" stroke="#0284c7" stroke-width="2" />
        <circle cx="420" cy="38" r="8" fill="#0369a1" />
        <text x="420" y="42" font-size="11" font-weight="700" fill="#ffffff" text-anchor="middle">5</text>
      </g>

      
      <g class="crest-elem" id="crest-6">
        <rect x="496" y="8" width="28" height="88" fill="url(#crestGrad)" rx="3" />
        <line x1="510" y1="8" x2="510" y2="96" stroke="#0284c7" stroke-width="2" />
        <circle cx="510" cy="38" r="8" fill="#0369a1" />
        <text x="510" y="42" font-size="11" font-weight="700" fill="#ffffff" text-anchor="middle">6</text>
      </g>

      
      <g id="gap-spans" font-size="11.5" font-weight="700" fill="#0284c7" text-anchor="middle">
        <g class="gap-elem" id="gap-1">
          <line x1="63" y1="74" x2="147" y2="74" stroke="#0284c7" stroke-width="1.6" marker-start="url(#subArrowL)" marker-end="url(#subArrowR)" />
          <rect x="91" y="63" width="28" height="18" fill="#ffffff" stroke="#bae6fd" stroke-width="1" rx="4" />
          <text x="105" y="76.5">λ₁</text>
        </g>
        <g class="gap-elem" id="gap-2">
          <line x1="153" y1="74" x2="237" y2="74" stroke="#0284c7" stroke-width="1.6" marker-start="url(#subArrowL)" marker-end="url(#subArrowR)" />
          <rect x="181" y="63" width="28" height="18" fill="#ffffff" stroke="#bae6fd" stroke-width="1" rx="4" />
          <text x="195" y="76.5">λ₂</text>
        </g>
        <g class="gap-elem" id="gap-3">
          <line x1="243" y1="74" x2="327" y2="74" stroke="#0284c7" stroke-width="1.6" marker-start="url(#subArrowL)" marker-end="url(#subArrowR)" />
          <rect x="271" y="63" width="28" height="18" fill="#ffffff" stroke="#bae6fd" stroke-width="1" rx="4" />
          <text x="285" y="76.5">λ₃</text>
        </g>
        <g class="gap-elem" id="gap-4">
          <line x1="333" y1="74" x2="417" y2="74" stroke="#0284c7" stroke-width="1.6" marker-start="url(#subArrowL)" marker-end="url(#subArrowR)" />
          <rect x="361" y="63" width="28" height="18" fill="#ffffff" stroke="#bae6fd" stroke-width="1" rx="4" />
          <text x="375" y="76.5">λ₄</text>
        </g>
        <g class="gap-elem" id="gap-5">
          <line x1="423" y1="74" x2="507" y2="74" stroke="#0284c7" stroke-width="1.6" marker-start="url(#subArrowL)" marker-end="url(#subArrowR)" />
          <rect x="451" y="63" width="28" height="18" fill="#ffffff" stroke="#bae6fd" stroke-width="1" rx="4" />
          <text x="465" y="76.5">λ₅</text>
        </g>
      </g>

      
      <g class="bracket-group" id="mainBracket">
        
        <line x1="60" y1="98" x2="60" y2="140" stroke="#94a3b8" stroke-dasharray="3,3" stroke-width="1.2" />
        <line x1="510" y1="98" x2="510" y2="140" stroke="#94a3b8" stroke-dasharray="3,3" stroke-width="1.2" />

        
        <line x1="64" y1="120" x2="506" y2="120" stroke="#0369a1" stroke-width="2" marker-start="url(#arrowL)" marker-end="url(#arrowR)" />

        
        <rect x="145" y="108" width="280" height="24" rx="12" fill="#0369a1" />
        <text id="bracketText" x="285" y="124.5" font-size="12" font-weight="700" fill="#ffffff" text-anchor="middle" letter-spacing="0.2">
          Total distance = 15.0 cm (5 wavelengths)
        </text>
      </g>

      
      <g id="ruler" transform="translate(60, 150)">
        
        <rect x="-12" y="0" width="500" height="42" rx="4" fill="#fef08a" stroke="#ca8a04" stroke-width="1.5" />

        
        
        <line x1="0" y1="0" x2="0" y2="16" stroke="#1e2945" stroke-width="1.5" />
        <text x="0" y="29" font-size="11" font-weight="700" fill="#1e2945" text-anchor="middle">0</text>

        
        <line x1="30" y1="0" x2="30" y2="10" stroke="#1e2945" stroke-width="1" />
        <line x1="60" y1="0" x2="60" y2="10" stroke="#1e2945" stroke-width="1" />

        
        <line x1="90" y1="0" x2="90" y2="16" stroke="#1e2945" stroke-width="1.5" />
        <text x="90" y="29" font-size="11" font-weight="700" fill="#1e2945" text-anchor="middle">3</text>

        <line x1="120" y1="0" x2="120" y2="10" stroke="#1e2945" stroke-width="1" />
        <line x1="150" y1="0" x2="150" y2="10" stroke="#1e2945" stroke-width="1" />

        
        <line x1="180" y1="0" x2="180" y2="16" stroke="#1e2945" stroke-width="1.5" />
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    <div class="interactive-row">
      <button class="btn active" id="btn-all" onclick="showMode('all')">All 5 Wavelengths</button>
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    <div class="calc-card">
      <div class="formula-line" id="formulaText">
        <span>Wavelength (λ)</span>
        <span>=</span>
        <span>15.0 cm ÷ 5</span>
        <span>=</span>
        <span class="highlight-badge">3.0 cm = 0.03 m</span>
      </div>
      <div class="note-text" id="noteText">
        Measuring across multiple waves reduces measurement uncertainty.
      </div>
    </div>
  </div>

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          <span>Wavelength (λ)</span>
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        note.textContent = 'Distance between two consecutive wave crests represents one full wavelength (λ).';
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    }
  </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>Wave Speed Equation</title>
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      border: 2px dashed #cbd5e1;
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</head>
<body>
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        <span class="sym-op">=</span>
        <span class="sym-f" id="eqF">f</span>
        <span class="sym-op">×</span>
        <span class="sym-l" id="eqL">λ</span>
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    <div class="pills-grid">
      <div class="pill" id="pillV" onclick="selectVar('v')">
        <div class="pill-symbol sym-v">v</div>
        <div class="pill-name">Wave Speed</div>
        <div class="pill-unit">m/s</div>
      </div>
      <div class="pill" id="pillF" onclick="selectVar('f')">
        <div class="pill-symbol sym-f">f</div>
        <div class="pill-name">Frequency</div>
        <div class="pill-unit">Hz</div>
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        <div class="pill-symbol sym-l">λ</div>
        <div class="pill-name">Wavelength</div>
        <div class="pill-unit">m</div>
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    </div>

    
    <div class="substitution-card">
      <div class="sub-header">
        <span class="sub-title">Worked Example</span>
        <div class="presets">
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          <button class="preset-btn" id="btnEx2" onclick="setExample(5, 0.08, this)">Deep Water</button>
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        <span class="sym-op">=</span>
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      const speed = (f * l).toFixed(2);
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      document.getElementById('valL').textContent = l;
      document.getElementById('valRes').textContent = speed;
    }
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</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <style>
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</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>
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</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>

UK-GCSE-SCIENCE-PHYS-WAV-01

Child standards (3)

Aligned learning resources

Related diagrams