<!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;
      -webkit-tap-highlight-color: transparent;
    }

    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #f8fafc;
      color: #1e2945;
      padding: 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
      user-select: none;
    }

    .nav-tabs {
      display: flex;
      gap: 6px;
      width: 100%;
      max-width: 500px;
      margin-bottom: 8px;
    }

    .tab-btn {
      flex: 1;
      border: 1px solid #cbd5e1;
      background: #ffffff;
      color: #64748b;
      padding: 8px 4px;
      font-size: 13px;
      font-weight: 700;
      border-radius: 8px;
      cursor: pointer;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 4px;
      transition: all 0.2s ease;
    }

    .tab-btn.active {
      background: #2563eb;
      color: #ffffff;
      border-color: #2563eb;
      box-shadow: 0 2px 6px rgba(37, 99, 235, 0.25);
    }

    .content-area {
      position: relative;
      width: 100%;
      max-width: 500px;
      height: 250px;
      overflow: hidden;
    }

    .rule-panel {
      position: absolute;
      inset: 0;
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 10px;
      opacity: 0;
      pointer-events: none;
      transition: opacity 0.3s ease;
    }

    .rule-panel.active {
      opacity: 1;
      pointer-events: auto;
    }

    .comparison-box {
      background: #ffffff;
      border-radius: 12px;
      border: 2px solid #e2e8f0;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      padding: 10px 8px;
      position: relative;
    }

    .comparison-box.correct {
      border-color: #86efac;
      background: #f0fdf4;
    }

    .comparison-box.incorrect {
      border-color: #fca5a5;
      background: #fef2f2;
    }

    .status-badge {
      font-size: 13px;
      font-weight: 800;
      padding: 3px 8px;
      border-radius: 12px;
      display: flex;
      align-items: center;
      gap: 4px;
      letter-spacing: 0.02em;
    }

    .badge-correct {
      background: #dcfce7;
      color: #15803d;
      border: 1px solid #86efac;
    }

    .badge-incorrect {
      background: #fee2e2;
      color: #b91c1c;
      border: 1px solid #fca5a5;
    }

    .svg-stage {
      width: 100%;
      height: 150px;
      display: flex;
      align-items: center;
      justify-content: center;
    }

    .rule-caption {
      font-size: 13px;
      font-weight: 700;
      color: #334155;
      text-align: center;
    }

    /* Controls bar */
    .controls {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 12px;
      margin-top: 8px;
      width: 100%;
      max-width: 500px;
    }

    .ctrl-btn {
      background: #ffffff;
      border: 1px solid #cbd5e1;
      border-radius: 6px;
      width: 34px;
      height: 30px;
      display: flex;
      align-items: center;
      justify-content: center;
      cursor: pointer;
      font-size: 13px;
      color: #334155;
      font-weight: bold;
    }

    .dots-indicator {
      display: flex;
      gap: 6px;
    }

    .dot {
      width: 8px;
      height: 8px;
      border-radius: 50%;
      background: #cbd5e1;
      cursor: pointer;
      transition: background 0.2s ease;
    }

    .dot.active {
      background: #2563eb;
      transform: scale(1.2);
    }
  </style>
</head>
<body>

  
  <div class="nav-tabs">
    <button class="tab-btn active" id="tab0" onclick="goToRule(0)">1. Direction</button>
    <button class="tab-btn" id="tab1" onclick="goToRule(1)">2. Length</button>
    <button class="tab-btn" id="tab2" onclick="goToRule(2)">3. External</button>
  </div>

  
  <div class="content-area">

    
    <div class="rule-panel active" id="panel0">
      <div class="comparison-box correct">
        <span class="status-badge badge-correct">✓ Outward</span>
        <div class="svg-stage">
          <svg viewBox="0 0 140 140" width="130" height="130">
            <defs>
              <marker id="mGreen" markerWidth="6" markerHeight="6" refX="4" refY="3" orient="auto">
                <polygon points="0 1, 5 3, 0 5" fill="#16a34a" />
              </marker>
            </defs>
            
            <line x1="70" y1="70" x2="70" y2="18" stroke="#16a34a" stroke-width="3.5" marker-end="url(#mGreen)" />
            <line x1="70" y1="70" x2="70" y2="122" stroke="#16a34a" stroke-width="3.5" marker-end="url(#mGreen)" />
            <line x1="70" y1="70" x2="122" y2="70" stroke="#16a34a" stroke-width="3.5" marker-end="url(#mGreen)" />
            <line x1="70" y1="70" x2="18" y2="70" stroke="#16a34a" stroke-width="3.5" marker-end="url(#mGreen)" />
            
            <circle cx="70" cy="70" r="7" fill="#1e2945" />
          </svg>
        </div>
        <span class="rule-caption">Arrows away from dot</span>
      </div>

      <div class="comparison-box incorrect">
        <span class="status-badge badge-incorrect">✗ Inward</span>
        <div class="svg-stage">
          <svg viewBox="0 0 140 140" width="130" height="130">
            <defs>
              <marker id="mRed" markerWidth="6" markerHeight="6" refX="4" refY="3" orient="auto">
                <polygon points="0 1, 5 3, 0 5" fill="#dc2626" />
              </marker>
            </defs>
            
            <line x1="70" y1="18" x2="70" y2="60" stroke="#dc2626" stroke-width="3.5" marker-end="url(#mRed)" />
            <line x1="70" y1="122" x2="70" y2="80" stroke="#dc2626" stroke-width="3.5" marker-end="url(#mRed)" />
            <line x1="18" y1="70" x2="60" y2="70" stroke="#dc2626" stroke-width="3.5" marker-end="url(#mRed)" />
            <line x1="122" y1="70" x2="80" y2="70" stroke="#dc2626" stroke-width="3.5" marker-end="url(#mRed)" />
            
            <circle cx="70" cy="70" r="7" fill="#1e2945" />
          </svg>
        </div>
        <span class="rule-caption">Never push into dot</span>
      </div>
    </div>

    
    <div class="rule-panel" id="panel1">
      <div class="comparison-box correct">
        <span class="status-badge badge-correct">✓ Balanced</span>
        <div class="svg-stage">
          <svg viewBox="0 0 140 140" width="130" height="130">
            <defs>
              <marker id="mBlue" markerWidth="6" markerHeight="6" refX="4" refY="3" orient="auto">
                <polygon points="0 1, 5 3, 0 5" fill="#2563eb" />
              </marker>
            </defs>
            
            <line x1="70" y1="70" x2="25" y2="70" stroke="#2563eb" stroke-width="3.5" marker-end="url(#mBlue)" />
            <line x1="70" y1="70" x2="115" y2="70" stroke="#2563eb" stroke-width="3.5" marker-end="url(#mBlue)" />
            <circle cx="70" cy="70" r="7" fill="#1e2945" />
            
            <text x="25" y="56" fill="#1e2945" font-size="12" font-weight="bold" text-anchor="middle">10 N</text>
            <text x="115" y="56" fill="#1e2945" font-size="12" font-weight="bold" text-anchor="middle">10 N</text>
          </svg>
        </div>
        <span class="rule-caption">Equal force = equal length</span>
      </div>

      <div class="comparison-box correct">
        <span class="status-badge badge-correct">✓ Unbalanced</span>
        <div class="svg-stage">
          <svg viewBox="0 0 140 140" width="130" height="130">
            
            <line x1="55" y1="70" x2="25" y2="70" stroke="#2563eb" stroke-width="3.5" marker-end="url(#mBlue)" />
            <line x1="55" y1="70" x2="135" y2="70" stroke="#2563eb" stroke-width="3.5" marker-end="url(#mBlue)" />
            <circle cx="55" cy="70" r="7" fill="#1e2945" />
            
            <text x="25" y="56" fill="#1e2945" font-size="12" font-weight="bold" text-anchor="middle">10 N</text>
            <text x="115" y="56" fill="#1e2945" font-size="12" font-weight="bold" text-anchor="middle">30 N</text>
          </svg>
        </div>
        <span class="rule-caption">Longer arrow = larger force</span>
      </div>
    </div>

    
    <div class="rule-panel" id="panel2">
      <div class="comparison-box correct">
        <span class="status-badge badge-correct">✓ ON Object</span>
        <div class="svg-stage">
          <svg viewBox="0 0 140 140" width="130" height="130">
            <defs>
              <marker id="mGreen3" markerWidth="6" markerHeight="6" refX="4" refY="3" orient="auto">
                <polygon points="0 1, 5 3, 0 5" fill="#16a34a" />
              </marker>
            </defs>
            <circle cx="70" cy="70" r="8" fill="#1e2945" />
            <line x1="70" y1="70" x2="70" y2="20" stroke="#16a34a" stroke-width="3.5" marker-end="url(#mGreen3)" />
            <line x1="70" y1="70" x2="70" y2="120" stroke="#16a34a" stroke-width="3.5" marker-end="url(#mGreen3)" />
            <text x="78" y="32" fill="#16a34a" font-size="11" font-weight="bold">Support</text>
            <text x="78" y="115" fill="#16a34a" font-size="11" font-weight="bold">Weight</text>
          </svg>
        </div>
        <span class="rule-caption">Forces acting ON body</span>
      </div>

      <div class="comparison-box incorrect">
        <span class="status-badge badge-incorrect">✗ BY Object</span>
        <div class="svg-stage">
          <svg viewBox="0 0 140 140" width="130" height="130">
            
            <rect x="25" y="100" width="90" height="6" rx="3" fill="#cbd5e1" />
            <circle cx="70" cy="50" r="8" fill="#1e2945" />
            
            <line x1="70" y1="100" x2="70" y2="132" stroke="#dc2626" stroke-width="3.5" stroke-dasharray="4 3" marker-end="url(#mRed)" />
            <text x="70" y="40" fill="#64748b" font-size="10" text-anchor="middle">Object</text>
            <text x="78" y="125" fill="#dc2626" font-size="11" font-weight="bold">On Floor</text>
          </svg>
        </div>
        <span class="rule-caption">Exclude forces exerted BY it</span>
      </div>
    </div>

  </div>

  
  <div class="controls">
    <button class="ctrl-btn" onclick="prevRule()" title="Previous">◀</button>
    <div class="dots-indicator">
      <div class="dot active" onclick="goToRule(0)"></div>
      <div class="dot" onclick="goToRule(1)"></div>
      <div class="dot" onclick="goToRule(2)"></div>
    </div>
    <button class="ctrl-btn" onclick="nextRule()" title="Next">▶</button>
    <button class="ctrl-btn" id="playToggle" onclick="togglePlay()" title="Auto-cycle">⏸</button>
  </div>

  <script>
    let currentRule = 0;
    let isPlaying = true;
    let timer = null;

    function showRule(index) {
      currentRule = index;
      for (let i = 0; i < 3; i++) {
        document.getElementById('tab' + i).classList.toggle('active', i === index);
        document.getElementById('panel' + i).classList.toggle('active', i === index);
        document.querySelectorAll('.dot')[i].classList.toggle('active', i === index);
      }
    }

    function goToRule(index) {
      showRule(index);
      resetAutoPlay();
    }

    function nextRule() {
      goToRule((currentRule + 1) % 3);
    }

    function prevRule() {
      goToRule((currentRule + 2) % 3);
    }

    function startAutoPlay() {
      stopAutoPlay();
      timer = setInterval(() => {
        showRule((currentRule + 1) % 3);
      }, 3500);
    }

    function stopAutoPlay() {
      if (timer) {
        clearInterval(timer);
        timer = null;
      }
    }

    function resetAutoPlay() {
      if (isPlaying) {
        startAutoPlay();
      }
    }

    function togglePlay() {
      isPlaying = !isPlaying;
      document.getElementById('playToggle').textContent = isPlaying ? '⏸' : '▶';
      if (isPlaying) {
        startAutoPlay();
      } else {
        stopAutoPlay();
      }
    }

    // Initialize auto play
    startAutoPlay();
  </script>
</body>
</html>

Drawing Free Body Diagrams for Isolated Objects

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

    body {
      width: 100%;
      min-height: 100vh;
      background: #ffffff;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      padding: 12px;
      color: #1e293b;
    }

    .fbd-container {
      width: 100%;
      max-width: 360px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 12px;
    }

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

    .grid-line {
      stroke: #f1f5f9;
      stroke-width: 1;
    }

    .axis-line {
      stroke: #cbd5e1;
      stroke-width: 1.25;
      stroke-dasharray: 4,4;
    }

    .force-arrow {
      stroke: #0284c7;
      stroke-width: 3;
      stroke-linecap: round;
    }

    .tick-mark {
      stroke: #0284c7;
      stroke-width: 2.5;
      stroke-linecap: round;
    }

    .force-title {
      font-size: 13px;
      font-weight: 700;
      fill: #0f172a;
    }

    .force-value {
      font-size: 12px;
      font-weight: 600;
      fill: #0284c7;
    }

    .book-box {
      fill: #f8fafc;
      stroke: #334155;
      stroke-width: 2;
      rx: 4px;
    }

    .book-text {
      font-size: 13px;
      font-weight: 700;
      fill: #1e293b;
      letter-spacing: 0.5px;
      text-anchor: middle;
      dominant-baseline: central;
    }

    .grid-scale-note {
      font-size: 11px;
      fill: #64748b;
      font-weight: 500;
    }

    .equilibrium-badge {
      background: #f0fdf4;
      border: 1px solid #86efac;
      color: #166534;
      padding: 6px 14px;
      border-radius: 9999px;
      font-size: 12.5px;
      font-weight: 700;
      text-align: center;
      line-height: 1.3;
    }

    @media (max-width: 360px) {
      .force-title { font-size: 12px; }
      .force-value { font-size: 11px; }
      .equilibrium-badge { font-size: 11.5px; padding: 5px 12px; }
    }
  </style>
</head>
<body>

  <div class="fbd-container">
    <svg viewBox="0 0 340 300" aria-label="Free body diagram of a stationary book in static equilibrium">
      <defs>
        
        <pattern id="grid" width="20" height="20" patternUnits="userSpaceOnUse">
          <path d="M 20 0 L 0 0 0 20" fill="none" class="grid-line" />
        </pattern>

        
        <marker id="arrow" viewBox="0 0 10 10" refX="7" refY="5" markerWidth="6" markerHeight="6" orient="auto">
          <path d="M 1 2 L 8 5 L 1 8 Z" fill="#0284c7" stroke="#0284c7" stroke-width="1" stroke-linejoin="round" />
        </marker>
      </defs>

      
      <rect x="0" y="0" width="340" height="300" fill="url(#grid)" />

      
      <line x1="170" y1="15" x2="170" y2="285" class="axis-line" />

      
      <text x="12" y="22" class="grid-scale-note">1 grid unit = 4.9 N</text>

      
      <line x1="170" y1="130" x2="170" y2="50" class="force-arrow" marker-end="url(#arrow)" />
      
      
      <line x1="163" y1="90" x2="177" y2="90" class="tick-mark" />

      
      <text x="186" y="68" class="force-title">Normal Force (N)</text>
      <text x="186" y="86" class="force-value">N = 19.6 N (↑)</text>

      
      <rect x="125" y="130" width="90" height="40" class="book-box" />
      <text x="170" y="150" class="book-text">Book</text>

      
      <line x1="170" y1="170" x2="170" y2="250" class="force-arrow" marker-end="url(#arrow)" />

      
      <line x1="163" y1="210" x2="177" y2="210" class="tick-mark" />

      
      <text x="186" y="222" class="force-title">Weight (W)</text>
      <text x="186" y="240" class="force-value">W = 19.6 N (↓)</text>
    </svg>

    
    <div class="equilibrium-badge">
      Resultant Force = 0 N (Static Equilibrium)
    </div>
  </div>

</body>
</html>

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

    .step-btn {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      color: #475569;
      font-size: 13px;
      font-weight: 600;
      padding: 6px 12px;
      border-radius: 6px;
      cursor: pointer;
      transition: background 0.2s, color 0.2s, border-color 0.2s;
    }

    .step-btn.active {
      background: #2563eb;
      border-color: #2563eb;
      color: #ffffff;
    }

    .svg-container {
      width: 100%;
      max-width: 520px;
      flex-grow: 1;
      display: flex;
      align-items: center;
      justify-content: center;
    }

    svg {
      width: 100%;
      height: auto;
      overflow: visible;
    }

    .force-arrow {
      transition: opacity 0.3s ease, stroke-width 0.3s ease;
    }

    .dimmed {
      opacity: 0.2;
    }

    .highlight {
      filter: drop-shadow(0 0 3px rgba(37, 99, 235, 0.4));
    }
  </style>
</head>
<body>

  <div class="controls">
    <button class="step-btn active" id="btn-all" onclick="setMode('all')">All Forces</button>
    <button class="step-btn" id="btn-vert" onclick="setMode('vert')">Vertical (Balanced)</button>
    <button class="step-btn" id="btn-horiz" onclick="setMode('horiz')">Horizontal (Resultant)</button>
  </div>

  <div class="svg-container">
    <svg viewBox="0 0 520 340" aria-label="Free body diagram of an accelerating car">
      <defs>
        
        <marker id="arrow-blue" viewBox="0 0 10 10" refX="6" refY="5" markerWidth="6" markerHeight="6" orient="auto-start-reverse">
          <path d="M 0 1 L 10 5 L 0 9 z" fill="#2563eb" />
        </marker>
        
        <marker id="arrow-amber" viewBox="0 0 10 10" refX="6" refY="5" markerWidth="6" markerHeight="6" orient="auto-start-reverse">
          <path d="M 0 1 L 10 5 L 0 9 z" fill="#d97706" />
        </marker>
        
        <marker id="arrow-purple" viewBox="0 0 10 10" refX="6" refY="5" markerWidth="6" markerHeight="6" orient="auto-start-reverse">
          <path d="M 0 1 L 10 5 L 0 9 z" fill="#7c3aed" />
        </marker>
      </defs>

      
      <line x1="30" y1="260" x2="490" y2="260" stroke="#cbd5e1" stroke-width="2" stroke-dasharray="6 4" />

      
      <g id="grp-resultant" class="force-arrow">
        <line x1="250" y1="42" x2="350" y2="42" stroke="#7c3aed" stroke-width="3" stroke-dasharray="5 3" marker-end="url(#arrow-purple)" />
        <text x="300" y="28" font-size="13" font-weight="bold" fill="#7c3aed" text-anchor="middle">Resultant = 2000 N →</text>
      </g>

      
      <g id="grp-vertical" class="force-arrow">
        
        <line x1="250" y1="165" x2="250" y2="95" stroke="#2563eb" stroke-width="3" marker-end="url(#arrow-blue)" />
        <text x="250" y="85" font-size="14" font-weight="600" fill="#2563eb" text-anchor="middle">Normal (N)</text>

        
        <line x1="250" y1="215" x2="250" y2="285" stroke="#2563eb" stroke-width="3" marker-end="url(#arrow-blue)" />
        <text x="250" y="303" font-size="14" font-weight="600" fill="#2563eb" text-anchor="middle">Weight (W)</text>
      </g>

      
      <g id="grp-horizontal" class="force-arrow">
        
        <line x1="220" y1="190" x2="180" y2="190" stroke="#d97706" stroke-width="3" marker-end="url(#arrow-amber)" />
        <text x="170" y="186" font-size="13" font-weight="600" fill="#d97706" text-anchor="end">Drag + Friction</text>
        <text x="170" y="202" font-size="12" font-weight="bold" fill="#d97706" text-anchor="end">1000 N</text>

        
        <line x1="280" y1="190" x2="400" y2="190" stroke="#2563eb" stroke-width="3" marker-end="url(#arrow-blue)" />
        <text x="410" y="186" font-size="13" font-weight="600" fill="#2563eb" text-anchor="start">Thrust</text>
        <text x="410" y="202" font-size="12" font-weight="bold" fill="#2563eb" text-anchor="start">3000 N</text>
      </g>

      
      <rect x="220" y="165" width="60" height="50" rx="6" fill="#f8fafc" stroke="#1e2945" stroke-width="2" />
      <text x="250" y="195" font-size="14" font-weight="bold" fill="#1e2945" text-anchor="middle">Car</text>
    </svg>
  </div>

  <script>
    function setMode(mode) {
      const gVert = document.getElementById('grp-vertical');
      const gHoriz = document.getElementById('grp-horizontal');
      const gRes = document.getElementById('grp-resultant');
      
      document.querySelectorAll('.step-btn').forEach(btn => btn.classList.remove('active'));

      if (mode === 'all') {
        document.getElementById('btn-all').classList.add('active');
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<!DOCTYPE html>
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<head>
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UK-GCSE-SCIENCE-PHYS-FOR-01-03

Aligned learning resources

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