Pendulum: a physics lab in your browser

What you’ll get

The pendulum swings for real, a trail follows the weight, and a graph of the angle is drawn below. Change the length, angle, mass and planet — and watch how the period changes. Press “Play the example” above — Gemini made it from the prompt below.

Steps

1. Open gemini.google.com. Under 13 — together with a parent, on their device.

2. Copy the whole prompt and send it:

   Make a pendulum model in a single HTML file. Don't load anything from the internet: no Tailwind, no CDN, no fonts, no images and no libraries — only your own CSS and JavaScript inside the file. Don't save anything in the browser's memory. Draw on a canvas a pendulum that swings for real (don't use the small-angle approximation). Sliders: string length from 0.2 to 2 m, starting angle from 5° to 80°, mass of the weight. A planet switch: Earth, Moon, Jupiter. Show the measured swing period and, next to it, the formula T = 2π√(L/g). A trail follows the weight, and below it a graph of angle versus time is drawn. "Pause" and "Restart" buttons. Everything should look good on a phone. Show the result in Canvas.
   

3. Wait about a minute, click Preview and try all the buttons and sliders.

4. Check the AI (see the question above).

5. Click Download (sometimes it’s under the Export menu) — the file opens in any browser. Show it in class!

Change the prompt

Before sending, swap a few words and you get your own version. Change only the words, and leave the rules about the internet and Canvas as they are.

• “Earth, Moon, Jupiter” → “Earth, Mars, Pluto”
• “from 0.2 to 2 m” → “from 0.1 to 5 m”

If it doesn’t work

• The AI says it changed everything, but the result is the same? Write: Nothing changed. Show the updated version in Canvas.
• No Preview button? Write: Show the result in Canvas.
• The pendulum froze? Write: “The pendulum doesn’t swing after I press Restart. Fix it, change nothing else.”