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Override for the tutor's lesson content generation calls. Auto uses the system default (Claude Sonnet 5 for lesson text, Opus 5 for diagrams).

Lesson generation model

System default

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Tutoring abilities

Imagine leaving a chocolate bar in your pocket on a warm sunny day. When you reach in to grab a snack, you don't find a crunchy bar—you find a warm, gooey puddle.

What made that hard bar turn into runny goop?

Everything around us is made of tiny building blocks called particles. In a **solid**, these particles are packed tightly together in fixed positions, shaking in place.

When you add heat, you give the particles **thermal energy** (heat energy), making them jiggle faster and faster until they break free to slide past each other as a **liquid**.

<!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>Heating and Melting</title>
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, sans-serif;
      background: #f8f9fa;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
      padding: 12px;
      user-select: none;
    }

    .controls {
      display: flex;
      gap: 8px;
      width: 100%;
      max-width: 480px;
      justify-content: center;
    }

    .btn-step {
      flex: 1;
      padding: 8px 12px;
      font-size: 14px;
      font-weight: 600;
      border: 1px solid #e2e8f0;
      background: #ffffff;
      color: #6b7280;
      border-radius: 8px;
      cursor: pointer;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      transition: background 0.2s, color 0.2s, box-shadow 0.2s;
    }

    .btn-step.active {
      background: #22b7ff;
      color: #ffffff;
      box-shadow: 0 2px 8px rgba(34, 183, 255, 0.35);
      border-color: #22b7ff;
    }

    .sim-container {
      position: relative;
      width: 100%;
      max-width: 480px;
      height: 250px;
      background: #ffffff;
      border-radius: 12px;
      box-shadow: 0 2px 12px rgba(0, 0, 0, 0.05);
      display: flex;
      align-items: center;
      justify-content: center;
      overflow: hidden;
    }

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

    .heat-bar-wrap {
      width: 100%;
      max-width: 480px;
      display: flex;
      align-items: center;
      gap: 12px;
      background: #ffffff;
      padding: 8px 14px;
      border-radius: 10px;
      box-shadow: 0 1px 4px rgba(0, 0, 0, 0.04);
    }

    .heat-label {
      font-size: 13px;
      font-weight: 700;
      color: #475569;
      white-space: nowrap;
    }

    .track {
      flex: 1;
      height: 10px;
      background: #e2e8f0;
      border-radius: 5px;
      overflow: hidden;
      position: relative;
    }

    .fill {
      height: 100%;
      width: 15%;
      border-radius: 5px;
      background: linear-gradient(90deg, #22b7ff, #ff9800, #ff4444);
      transition: width 0.4s ease;
    }
  </style>
</head>
<body>

  
  <div class="controls">
    <button class="btn-step active" id="btn-solid">Solid 🧊</button>
    <button class="btn-step" id="btn-heating">Heating 🔥</button>
    <button class="btn-step" id="btn-liquid">Liquid 💧</button>
  </div>

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

  
  <div class="heat-bar-wrap">
    <span class="heat-label">Thermal Energy</span>
    <div class="track">
      <div class="fill" id="heatFill"></div>
    </div>
  </div>

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

    const btnSolid = document.getElementById('btn-solid');
    const btnHeating = document.getElementById('btn-heating');
    const btnLiquid = document.getElementById('btn-liquid');
    const buttons = [btnSolid, btnHeating, btnLiquid];

    let state = 'solid'; // 'solid' | 'heating' | 'liquid'
    let width, height;
    let particles = [];
    const NUM_COLS = 6;
    const NUM_ROWS = 5;
    const RADIUS = 11;

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

    function initParticles() {
      particles = [];
      const spacing = RADIUS * 2 + 3;
      const startX = width / 2 - ((NUM_COLS - 1) * spacing) / 2;
      const startY = height - 40 - (NUM_ROWS * spacing);

      for (let r = 0; r < NUM_ROWS; r++) {
        for (let c = 0; c < NUM_COLS; c++) {
          const gridX = startX + c * spacing;
          const gridY = startY + r * spacing;
          particles.push({
            x: gridX,
            y: gridY,
            vx: (Math.random() - 0.5) * 1.5,
            vy: (Math.random() - 0.5) * 1.5,
            gridX: gridX,
            gridY: gridY,
            phase: Math.random() * Math.PI * 2
          });
        }
      }
    }

    function setState(newState) {
      state = newState;
      buttons.forEach(b => b.classList.remove('active'));

      if (state === 'solid') {
        btnSolid.classList.add('active');
        heatFill.style.width = '15%';
      } else if (state === 'heating') {
        btnHeating.classList.add('active');
        heatFill.style.width = '55%';
      } else {
        btnLiquid.classList.add('active');
        heatFill.style.width = '100%';
        // Give particles initial kick when entering liquid
        particles.forEach(p => {
          p.vx = (Math.random() - 0.5) * 3;
          p.vy = (Math.random() - 0.5) * 2;
        });
      }
    }

    btnSolid.onclick = () => setState('solid');
    btnHeating.onclick = () => setState('heating');
    btnLiquid.onclick = () => setState('liquid');

    // Beaker bounds
    function getBeaker() {
      const bW = Math.min(width * 0.78, 300);
      const bH = 160;
      const bX = (width - bW) / 2;
      const bY = height - bH - 24;
      return { x: bX, y: bY, w: bW, h: bH };
    }

    let time = 0;
    function update() {
      time += 0.05;
      const beaker = getBeaker();
      const bottom = beaker.y + beaker.h - RADIUS - 2;
      const left = beaker.x + RADIUS + 4;
      const right = beaker.x + beaker.w - RADIUS - 4;

      particles.forEach(p => {
        if (state === 'solid') {
          // Fixed lattice, gentle vibration
          const vibAmp = 1.2;
          p.x = p.gridX + Math.sin(time * 8 + p.phase) * vibAmp;
          p.y = p.gridY + Math.cos(time * 8 + p.phase) * vibAmp;
        } else if (state === 'heating') {
          // Rapid intense vibration, still bound
          const vibAmp = 3.8;
          p.x = p.gridX + (Math.random() - 0.5) * vibAmp * 2;
          p.y = p.gridY + (Math.random() - 0.5) * vibAmp * 2;
        } else if (state === 'liquid') {
          // Free fluid motion, gravity + sliding
          p.vy += 0.12; // gravity
          p.x += p.vx;
          p.y += p.vy;

          // Jiggle/fluid drift
          p.vx += (Math.random() - 0.5) * 0.4;
          p.vx *= 0.98;
          p.vy *= 0.98;

          // Wall bounds
          if (p.x < left) { p.x = left; p.vx *= -0.7; }
          if (p.x > right) { p.x = right; p.vx *= -0.7; }
          if (p.y > bottom) { p.y = bottom; p.vy *= -0.4; }
          if (p.y < beaker.y) { p.y = beaker.y; p.vy *= -0.7; }

          // Particle-particle soft repulsion
          particles.forEach(other => {
            if (p === other) return;
            const dx = other.x - p.x;
            const dy = other.y - p.y;
            const dist = Math.hypot(dx, dy);
            const minDist = RADIUS * 2;
            if (dist < minDist && dist > 0) {
              const overlap = (minDist - dist) * 0.5;
              const nx = dx / dist;
              const ny = dy / dist;
              p.x -= nx * overlap * 0.4;
              p.y -= ny * overlap * 0.4;
              other.x += nx * overlap * 0.4;
              other.y += ny * overlap * 0.4;
            }
          });
        }
      });
    }

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

      const beaker = getBeaker();

      // Draw Beaker
      ctx.lineWidth = 4;
      ctx.strokeStyle = '#cbd5e1';
      ctx.lineCap = 'round';
      ctx.beginPath();
      ctx.moveTo(beaker.x, beaker.y);
      ctx.lineTo(beaker.x, beaker.y + beaker.h);
      ctx.lineTo(beaker.x + beaker.w, beaker.y + beaker.h);
      ctx.lineTo(beaker.x + beaker.w, beaker.y);
      ctx.stroke();

      // Heat Flame / Glow under beaker
      if (state !== 'solid') {
        const flameY = beaker.y + beaker.h + 12;
        const numFlames = state === 'liquid' ? 5 : 3;
        for (let i = 0; i < numFlames; i++) {
          const fx = beaker.x + (beaker.w / (numFlames + 1)) * (i + 1);
          const fH = (state === 'liquid' ? 14 : 9) + Math.sin(time * 12 + i) * 3;
          ctx.fillStyle = state === 'liquid' ? '#ff4444' : '#ff9800';
          ctx.beginPath();
          ctx.arc(fx, flameY - fH / 2, 7, 0, Math.PI * 2);
          ctx.fill();
        }
      }

      // Draw Particles
      particles.forEach(p => {
        let grad = ctx.createRadialGradient(p.x - 3, p.y - 3, 2, p.x, p.y, RADIUS);

        if (state === 'solid') {
          grad.addColorStop(0, '#7dd3fc');
          grad.addColorStop(1, '#0284c7');
        } else if (state === 'heating') {
          grad.addColorStop(0, '#fed7aa');
          grad.addColorStop(1, '#ea580c');
        } else {
          grad.addColorStop(0, '#67e8f9');
          grad.addColorStop(1, '#0284c7');
        }

        ctx.fillStyle = grad;
        ctx.beginPath();
        ctx.arc(p.x, p.y, RADIUS, 0, Math.PI * 2);
        ctx.fill();

        ctx.strokeStyle = 'rgba(255,255,255,0.6)';
        ctx.lineWidth = 1.5;
        ctx.stroke();
      });
    }

    function loop() {
      update();
      draw();
      requestAnimationFrame(loop);
    }

    window.addEventListener('resize', resize);
    window.addEventListener('load', () => {
      resize();
      loop();
    });
  </script>
</body>
</html>

This change of state from a solid to a liquid is called **melting**.

Do all solids need the exact same amount of heat to melt?

Different solids hold onto their particles with different strengths, so each material needs a different amount of thermal energy to melt.

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #f8f9fa;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100vh;
      padding: 12px;
      user-select: none;
    }

    .main-view {
      width: 100%;
      max-width: 440px;
      flex: 1;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      gap: 12px;
    }

    .sim-card {
      width: 100%;
      background: #ffffff;
      border: 1px solid #e6e6e6;
      border-radius: 12px;
      box-shadow: 0 2px 8px rgba(0,0,0,0.04);
      display: flex;
      flex-direction: column;
      align-items: center;
      padding: 12px 12px 6px;
      position: relative;
    }

    .canvas-wrap {
      width: 100%;
      height: 220px;
      position: relative;
      display: flex;
      justify-content: center;
      align-items: center;
    }

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

    .flame-row {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      height: 36px;
      margin-top: 2px;
    }

    .flame-icon {
      font-size: 24px;
      transition: transform 0.3s ease, opacity 0.3s ease;
      filter: drop-shadow(0 2px 4px rgba(245, 158, 11, 0.4));
    }

    .controls {
      display: flex;
      width: 100%;
      max-width: 440px;
      gap: 8px;
      justify-content: center;
    }

    .btn {
      flex: 1;
      padding: 10px 8px;
      font-size: 15px;
      font-weight: 600;
      border-radius: 10px;
      border: 1px solid #e6e6e6;
      background: #ffffff;
      color: #1e2945;
      cursor: pointer;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      box-shadow: 0 1px 3px rgba(0,0,0,0.04);
      transition: all 0.2s ease;
    }

    .btn.active {
      background: #f59e0b;
      color: #ffffff;
      border-color: #f59e0b;
      box-shadow: 0 2px 8px rgba(245, 158, 11, 0.35);
    }
  </style>
</head>
<body>

  <div class="main-view">
    <div class="sim-card">
      <div class="canvas-wrap">
        <canvas id="simCanvas" width="360" height="220"></canvas>
      </div>
      <div class="flame-row" id="flameContainer">
        <span class="flame-icon" id="f1">🔥</span>
        <span class="flame-icon" id="f2">🔥</span>
        <span class="flame-icon" id="f3">🔥</span>
      </div>
    </div>

    <div class="controls">
      <button class="btn active" id="btn0" onclick="setMode(0)">🧊 Solid</button>
      <button class="btn" id="btn1" onclick="setMode(1)">⚡ Heating</button>
      <button class="btn" id="btn2" onclick="setMode(2)">💧 Liquid</button>
    </div>
  </div>

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

    const COLS = 6;
    const ROWS = 5;
    const NUM = COLS * ROWS;
    let mode = 0; // 0: Solid, 1: Heating, 2: Liquid

    const particles = [];
    const beaker = { x: 50, y: 15, w: 260, h: 185 };

    // Initialize grid particles
    for (let r = 0; r < ROWS; r++) {
      for (let c = 0; c < COLS; c++) {
        particles.push({
          gridX: beaker.x + 65 + c * 26,
          gridY: beaker.y + 60 + r * 25,
          x: beaker.x + 65 + c * 26,
          y: beaker.y + 60 + r * 25,
          vx: (Math.random() - 0.5) * 2,
          vy: (Math.random() - 0.5) * 2,
          radius: 9
        });
      }
    }

    function setMode(m) {
      mode = m;
      document.querySelectorAll('.btn').forEach((b, i) => {
        b.classList.toggle('active', i === m);
      });

      const flames = [document.getElementById('f1'), document.getElementById('f2'), document.getElementById('f3')];
      if (mode === 0) {
        flames.forEach(f => { f.style.opacity = '0.15'; f.style.transform = 'scale(0.7)'; });
      } else if (mode === 1) {
        flames[0].style.opacity = '0.3'; flames[0].style.transform = 'scale(0.85)';
        flames[1].style.opacity = '1'; flames[1].style.transform = 'scale(1.15)';
        flames[2].style.opacity = '0.3'; flames[2].style.transform = 'scale(0.85)';
      } else {
        flames.forEach(f => { f.style.opacity = '1'; f.style.transform = 'scale(1.25)'; });
      }
    }

    setMode(0);

    let stepTimer = 0;

    function update() {
      const pLen = particles.length;

      for (let i = 0; i < pLen; i++) {
        const p = particles[i];

        if (mode === 0) {
          // Solid: strong spring to lattice, tiny jitter
          const jx = (Math.random() - 0.5) * 1.2;
          const jy = (Math.random() - 0.5) * 1.2;
          p.x += (p.gridX - p.x) * 0.15 + jx;
          p.y += (p.gridY - p.y) * 0.15 + jy;
        } else if (mode === 1) {
          // Heating: loose spring, strong vibration
          const jx = (Math.random() - 0.5) * 5.5;
          const jy = (Math.random() - 0.5) * 5.5;
          p.x += (p.gridX - p.x) * 0.04 + jx;
          p.y += (p.gridY - p.y) * 0.04 + jy;
        } else {
          // Liquid: free fluid motion, settle at bottom
          p.vy += 0.15; // Gravity
          p.vx += (Math.random() - 0.5) * 0.5;
          p.vy += (Math.random() - 0.5) * 0.5;
          
          p.vx *= 0.98;
          p.vy *= 0.98;

          p.x += p.vx;
          p.y += p.vy;

          // Beaker boundary collisions
          const minX = beaker.x + p.radius + 6;
          const maxX = beaker.x + beaker.w - p.radius - 6;
          const maxY = beaker.y + beaker.h - p.radius - 4;
          const minY = beaker.y + 40;

          if (p.x < minX) { p.x = minX; p.vx *= -0.6; }
          if (p.x > maxX) { p.x = maxX; p.vx *= -0.6; }
          if (p.y > maxY) { p.y = maxY; p.vy *= -0.5; }
          if (p.y < minY) { p.y = minY; p.vy *= -0.5; }

          // Particle-particle repulsion
          for (let j = i + 1; j < pLen; j++) {
            const p2 = particles[j];
            const dx = p2.x - p.x;
            const dy = p2.y - p.y;
            const dist = Math.hypot(dx, dy);
            const minDist = p.radius + p2.radius + 1;
            if (dist < minDist && dist > 0) {
              const overlap = (minDist - dist) * 0.5;
              const nx = dx / dist;
              const ny = dy / dist;
              p.x -= nx * overlap;
              p.y -= ny * overlap;
              p2.x += nx * overlap;
              p2.y += ny * overlap;
              p.vx -= nx * 0.2;
              p.vy -= ny * 0.2;
              p2.vx += nx * 0.2;
              p2.vy += ny * 0.2;
            }
          }
        }
      }
    }

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

      // Draw Beaker
      ctx.lineWidth = 4;
      ctx.strokeStyle = '#94a3b8';
      ctx.lineCap = 'round';
      ctx.lineJoin = 'round';
      ctx.beginPath();
      ctx.moveTo(beaker.x, beaker.y);
      ctx.lineTo(beaker.x, beaker.y + beaker.h);
      ctx.lineTo(beaker.x + beaker.w, beaker.y + beaker.h);
      ctx.lineTo(beaker.x + beaker.w, beaker.y);
      ctx.stroke();

      // Draw bonds in solid & heating modes
      if (mode < 2) {
        ctx.lineWidth = mode === 0 ? 2 : 1;
        ctx.strokeStyle = mode === 0 ? 'rgba(34, 183, 255, 0.4)' : 'rgba(245, 158, 11, 0.25)';
        ctx.beginPath();
        for (let r = 0; r < ROWS; r++) {
          for (let c = 0; c < COLS; c++) {
            const idx = r * COLS + c;
            const p = particles[idx];
            // Right neighbor
            if (c < COLS - 1) {
              const pr = particles[idx + 1];
              ctx.moveTo(p.x, p.y);
              ctx.lineTo(pr.x, pr.y);
            }
            // Bottom neighbor
            if (r < ROWS - 1) {
              const pb = particles[idx + COLS];
              ctx.moveTo(p.x, p.y);
              ctx.lineTo(pb.x, pb.y);
            }
          }
        }
        ctx.stroke();
      }

      // Draw particles
      for (const p of particles) {
        ctx.beginPath();
        ctx.arc(p.x, p.y, p.radius, 0, Math.PI * 2);

        if (mode === 0) {
          ctx.fillStyle = '#22b7ff';
          ctx.strokeStyle = '#0284c7';
        } else if (mode === 1) {
          ctx.fillStyle = '#f59e0b';
          ctx.strokeStyle = '#d97706';
        } else {
          ctx.fillStyle = '#38bdf8';
          ctx.strokeStyle = '#0284c7';
        }

        ctx.fill();
        ctx.lineWidth = 1.5;
        ctx.stroke();

        // Highlight glint
        ctx.beginPath();
        ctx.arc(p.x - 3, p.y - 3, 2.5, 0, Math.PI * 2);
        ctx.fillStyle = 'rgba(255, 255, 255, 0.7)';
        ctx.fill();
      }
    }

    function loop() {
      update();
      draw();
      requestAnimationFrame(loop);
    }

    // Auto-advance loop every 3.5s if not manually interrupted
    setInterval(() => {
      stepTimer++;
      if (stepTimer >= 4) {
        setMode((mode + 1) % 3);
        stepTimer = 0;
      }
    }, 1000);

    window.setMode = (m) => {
      stepTimer = 0;
      setMode(m);
    };

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

Ice takes very little heat to melt, turning to water right in a normal room. Butter and chocolate need slightly more heat, melting easily from the warmth of your hand.

Candle wax holds its particles much tighter, meaning it needs higher thermal energy—like a hot flame—to turn into a smooth liquid.

Once a solid melts into a liquid, has it changed into a completely new substance forever?

Melting is a **reversible change** because no new substance is made. Melted chocolate is still chocolate, and melted wax is still wax.

If you take away the thermal energy by cooling the liquid down, the particles slow down, lock into place, and turn solid again.

Watch out for a common mix-up: **melting** requires only heat to turn one solid into a liquid, while **dissolving** requires two substances mixing together, like stirring sugar into tea!

science

Heating and Melting: Solids into Liquids. Observe and describe how heating provides thermal energy to melt ice, chocolate, butter, and candle wax into liquids.

KS2 Science: What Are Changes of State and Melting?

Changing State: Solid to Liquid (Heating and Melting)

States of Matter and Phase Changes: Heating and Cooling

Teaching strategies for Lower KS2 (Years 3-4): Use tactile, real-time demonstrations (such as melting chocolate drops, ice cubes, and butter buttons in dishes placed over warm water baths) to help pupils connect thermal energy transfer with changes of state. Explicitly contrast 'melting' with 'dissolving' using side-by-side experiments (e.g. heating butter vs. stirring sugar into water) to target the most persistent cognitive trap at this stage. Use mass-conservation pan balances before and after melting to demonstrate that melted liquid retains identical mass to the solid.

Heating and Melting: Solids into Liquids

What is Melting?

Four Familiar Solids