What is Hooke's law?
Pull twice as hard and a spring stretches twice as far. That one line from 1676 weighs your onions, clicks your pen, carries your car and tunes your guitar. Hang masses on 3D springs, bounce a car over a speed breaker, jump off a bridge on a bungee, and stretch steel until it snaps.
▶ Play with it · Read the 60-second explainer · Watch the 40-second video
- Twice the pull, twice the stretch. A spring stretches in proportion to the force on it: F = k × x. The spring constant k is its stiffness in newtons per metre. Plot force against stretch and you get a straight line whose slope is k. Springs end to end get softer; side by side, stiffer.
- Springs store energy and keep time. A stretched spring stores ½ k x², the area under the line. Let a mass bounce on it and each swing takes 2π √(m ÷ k), however big the bounce. That steady beat is why springs regulate watches.
- Weighing and clicking. Because stretch is proportional to load, a spring balance can have evenly spaced marks. It measures force, so on the Moon 6 kg of onions reads 1 kg. A click pen's spring pushes back with about 2 N.
- Riding on springs. A car's corner spring squeezes about 10 cm under its share of the weight and would bounce about 1.5 times a second, so a damper turns the bounce into heat. A bungee cord stores all the energy of a fall as ½ k x².
- Past the elastic limit. Steel obeys Hooke's law only to about 0.1 % stretch. Beyond its yield point it stays stretched, then necks and breaks. Rubber never follows a straight line. And for the same force, a softer spring stores more energy, not less.
| Term | Meaning |
|---|---|
| Hooke's law | The force on a spring is proportional to its extension: F = k × x. |
| Spring constant | A spring's stiffness, k, in newtons per metre: the force needed for each metre of stretch. |
| Extension | How much longer or shorter a spring is than its natural length. |
| Elastic energy | Energy stored in a stretched spring: ½ k x², the area under the force–extension line. |
| Period | The time for one bounce of a mass on a spring: T = 2π √(m ÷ k). |
| Young's modulus | A material's own stiffness: stress ÷ strain. About 200 GPa for steel. |
| Elastic limit | The largest stretch or stress after which a material still springs fully back. |
| Plastic deformation | A permanent change of shape once the elastic limit is passed. |
From twisted-sinew catapults to silicon springs in your phone, by way of a 1676 anagram.
- 1675 · A spiral spring keeps time (Christiaan Huygens, with the clockmaker Isaac Thuret, Paris, France)
- 1676 · The law as a puzzle (Robert Hooke, London, England)
- 1678 · 'As the extension, so the force' (Robert Hooke, London, England)
- 1807 · Young's modulus (Thomas Young, London, England)
- 1934 · Coil springs for every wheel (General Motors, Detroit, United States)
- 1979 · The first modern bungee jump (David Kirke and Simon Keeling, Oxford University Dangerous Sports Club, Clifton Suspension Bridge, Bristol, England)
- 1991 · Springs on a chip (Analog Devices, Massachusetts, United States)
The full story, with 20 moments, charts, people and 22 sources: glassbox.how/e/hookeclear/history. The data lives in history.json.
Made with the Glassbox studio from this box's storyboard (window.glassbox.director). Free to reuse under CC BY 4.0.
| File | What | Size |
|---|---|---|
glassbox/reel.mp4 |
Reel / Short, with captions and soundtrack | 1080×1920 |
glassbox/video.mp4 |
YouTube video, with captions and soundtrack | 1920×1080 |
glassbox/slide-1…10.jpg |
Instagram carousel | 1080×1350 |
glassbox/thumb.jpg |
YouTube thumbnail | 1280×720 |
glassbox/cover.jpg |
Share card and repo social preview | 1200×630 |
glassbox/history-reel.mp4 |
“History in 10 moments” Reel / Short | 1080×1920 |
glassbox/history-slide-*.jpg |
History carousel | 1080×1350 |
glassbox/post.json |
Post copy and schedule used by the publish kit |
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| Browser storage key | What it holds |
|---|---|
hookeclear.v1 |
Which chapters you have opened, your best quiz scores, and sound on or off. |
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python3 -m http.server 8000Three.js and the fonts ship in vendor/ and fonts/, so it also works offline.
Then open http://localhost:8000.
| File | What |
|---|---|
index.html, css/app.css |
The page and its styles |
js/app.js, js/stage.js, js/ui.js, js/kit.js |
The shared Glassbox 3D engine: chapters, 3D stage, controls, quiz, video director |
js/chapters/*.js |
One file per chapter: the 3D model, controls, text, key terms, quiz and video scenes |
js/hooke.js |
Shared parts and physics: a coil spring that re-shapes as it stretches, hooks, slotted masses, a metre rule, chart boards, g, Young's moduli and series/parallel spring constants |
glassbox.json |
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