Physics Classroom Games: Name the Observer Before the Displacement

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<html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width,initial-scale=1"><title>Physics Classroom Games: Name the Observer Before the Displacement</title><style>*{box-sizing:border-box}body{margin:0;color:var(--ink,#233342);background:var(--bg,#eef2f3);font:17px/1.6 system-ui,sans-serif}main{max-width:980px;margin:auto;padding:clamp(16px,4vw,38px)}h1{font:700 clamp(30px,5vw,49px)/1.12 Georgia,serif;margin:10px 0 20px;max-width:800px}h2{font-size:24px;line-height:1.3;margin:0 0 15px}h3{font-size:19px;margin:12px 0}p{margin:0 0 16px}.eyebrow{font-weight:750;letter-spacing:.08em;text-transform:uppercase;font-size:16px}header{padding:10px 0 25px;border-bottom:3px solid var(--accent,#24586d);margin-bottom:24px}.lede{font-size:20px;max-width:760px}.panel{background:var(--paper,#fff);padding:clamp(18px,3vw,28px);border:1px solid var(--line,#c6d1d8);border-radius:12px;margin:20px 0}.grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:20px}.grid>*{min-width:0}.row{display:flex;gap:12px;flex-wrap:wrap;align-items:center;margin:16px 0}.stack>*{margin:12px 0}button{font:700 17px/1.4 system-ui,sans-serif;cursor:pointer;color:white;background:var(--accent,#24586d);border:2px solid var(--accent,#24586d);border-radius:7px;padding:11px 17px;max-width:100%;overflow-wrap:anywhere}button.secondary{background:transparent;color:var(--ink,#233342)}button[aria-pressed=true]{box-shadow:inset 0 0 0 3px #fff;outline:2px solid var(--ink,#233342)}button:disabled{opacity:.55;cursor:default}input,textarea,select{font:17px/1.5 system-ui,sans-serif;color:inherit;background:white;border:1px solid #778591;padding:10px 12px;border-radius:6px;max-width:100%;width:100%;min-width:0}input[type=checkbox]{width:22px;height:22px}textarea{min-height:110px;resize:vertical}label{display:block;font-weight:700;margin:12px 0 7px}button:focus-visible,input:focus-visible,textarea:focus-visible,summary:focus-visible,[tabindex]:focus-visible{outline:3px solid #aa3d70;outline-offset:4px}.result{padding:18px;border-left:5px solid var(--accent,#24586d);background:var(--soft,#e5eff2);white-space:pre-wrap;overflow-wrap:anywhere;margin:20px 0}.result:empty{display:none}.hint{font-size:16px;color:var(--muted,#435968)}table{border-collapse:collapse;width:100%;table-layout:fixed;margin:16px 0}th,td{text-align:left;vertical-align:top;overflow-wrap:anywhere;padding:12px 8px;border-bottom:1px solid var(--line,#c6d1d8)}caption{text-align:left;font-weight:750;margin:8px 0}details{padding:18px;border:1px dashed #7b8b96;margin:20px 0}summary{cursor:pointer;font-weight:750}pre{font:16px/1.6 ui-monospace,monospace;white-space:pre-wrap;overflow-wrap:anywhere;background:#162735;color:#f5f8fa;padding:18px;border-radius:8px}canvas,svg{display:block;max-width:100%;height:auto}footer{margin:28px 0;font-size:16px}.badge{font-weight:750;color:var(--accent,#24586d)}.metric{font:700 38px/1.3 Georgia,serif}.board{display:grid;gap:5px;max-width:440px;margin:20px auto}.board button{padding:7px;min-height:45px}.sr{position:absolute;width:1px;height:1px;overflow:hidden;clip-path:inset(50%)}@media(max-width:560px){.grid{grid-template-columns:1fr}main{padding:16px}th,td{padding:10px 5px}.row button{flex-grow:1}.metric{font-size:32px}}
:root{--bg:#e9f0f3;--paper:#fff;--accent:#286775;--soft:#deeff2;--ink:#233e45}.axis{height:7px;background:#286775;margin:25px 0;position:relative}.axis:after{content:"→ +x, meters";position:absolute;right:0;top:7px;font-weight:700}.prediction{max-width:180px}</style></head><body><main><header><p class="eyebrow">Reference-frame lab · One shared clock</p><h1>Physics Classroom Games: Name the Observer Before the Displacement</h1><p class="lede">The same object moves four meters relative to the ground and zero relative to B.</p><p class="hint">Original fictional sample. Changes last only while this page remains open.</p></header><section class="panel"><h2>Supplied ground trajectories</h2><p>A = 1 + 2t · B = 2t · C = 6 · Ground origin = 0</p><table><caption>Shared times and ground positions, meters</caption><thead><tr><th>t, s</th><th>A</th><th>B</th><th>C</th></tr></thead><tbody><tr><td>0</td><td>1</td><td>0</td><td>6</td></tr><tr><td>1</td><td>3</td><td>2</td><td>6</td></tr><tr><td>2</td><td>5</td><td>4</td><td>6</td></tr></tbody></table><div class="axis" aria-hidden="true"></div></section><section class="panel"><h2 id="frame">Predict A relative to Ground</h2><div class="row"><button id="ground" type="button">Ground</button><button id="bframe" type="button">Moving B</button><button id="cframe" type="button">Stationary C</button></div><div class="grid"><div><label for="p0">A relative position at t=0, m</label><input id="p0" inputmode="decimal"></div><div><label for="p1">A relative position at t=1, m</label><input id="p1" inputmode="decimal"></div><div><label for="p2">A relative position at t=2, m</label><input id="p2" inputmode="decimal"></div><div><label for="delta">Displacement t=0 to 2, m</label><input id="delta" inputmode="decimal"></div></div><div class="row"><button id="check" type="button">Check prediction</button><button id="reset" type="button" class="secondary">Reset</button></div><p id="result" class="result" role="status"></p><label for="reason">Explain the observer and subtraction (teacher-reviewed)</label><textarea id="reason"></textarea><details><summary>Separate model key</summary><p>Ground: 1,3,5 → +4 m. B: 1,1,1 → 0 m. C: -5,-3,-1 → +4 m.</p></details></section><footer>Keep any records you need in your own working files. This page makes no network requests and saves no responses.</footer></main><script>
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let frame='Ground';const keys={Ground:[1,3,5,4],B:[1,1,1,0],C:[-5,-3,-1,4]};function clearFields(){for(const k of ['p0','p1','p2','delta','reason'])$(k).value='';$('result').textContent='';$('frame').textContent='Predict A relative to '+frame;}for(const[k,f]of [['ground','Ground'],['bframe','B'],['cframe','C']])$(k).addEventListener('click',()=>{frame=f;clearFields();});for(const k of ['p0','p1','p2','delta','reason'])$(k).addEventListener('input',()=>{$('result').textContent='';});$('check').addEventListener('click',()=>{const raw=['p0','p1','p2','delta'].map(k=>$(k).value.trim());if(raw.some(v=>!v||! /^[+-]?(?:\d+(?:\.\d*)?|\.\d+)$/.test(v)||!Number.isFinite(Number(v)))){$('result').textContent='Enter all three finite positions and displacement; zero is valid, blank is missing.';return;}const good=raw.every((v,i)=>Number(v)===keys[frame][i]),key=keys[frame],observer=frame==='B'?[0,2,4]:frame==='C'?[6,6,6]:[0,0,0];$('result').textContent=(good?'Numeric prediction matches. ':'Review the prediction. ')+'Frame '+frame+': positions '+key.slice(0,3).join(', ')+' m. Shared-time subtraction: 1 − '+observer[0]+' = '+key[0]+'; 3 − '+observer[1]+' = '+key[1]+'; 5 − '+observer[2]+' = '+key[2]+'. Displacement '+key[2]+' − ('+key[0]+') = '+key[3]+' m. The ground trajectories have not changed.';});$('reset').addEventListener('click',()=>{frame='Ground';clearFields();});
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