Newton's laws of motion

What are Newton's laws of motion?
Three rules written in 1687 still run every car, fan, dishwasher and spacecraft. Push a puck on frictionless ice, crash-test a car with and without a seat belt, race a car against a motorcycle, and find out where Newton finally breaks.

▶ Play with it  ·  Read the 60-second explainer  ·  Watch the 40-second video

In 60 seconds

1. Three rules for motion. Things keep still or keep moving in a straight line unless a force acts (inertia). A force makes them accelerate: a = F ÷ m. And forces come in pairs: push on something and it pushes back just as hard.
2. You keep going when the car stops. In a crash the car stops in under a tenth of a second, but you carry on. A seat belt stretches your stop over about 90 cm; without one you stop in centimetres against the wheel, with more than ten times the force.
3. Force, mass and power on the road. Off the line a car and a motorcycle accelerate about the same, around 5 m/s². Once moving, power-to-weight decides who pulls away. Turning needs a sideways push too, m v² ÷ r, which is why riders lean.
4. Every push pushes back. A dishwasher's spray arm spins because its slanted jets push it round. A fan throws air forward and is pushed back, and a rocket throws its exhaust out behind and is thrown forward, even in space.
5. Where Newton breaks. Near light speed momentum is γmv, not mv; inside atoms quantum mechanics takes over; in a spinning drum a fake centrifugal force appears. And heavy things don't fall faster: on the Moon, a hammer and a feather land together.

Words worth knowing

Term	Meaning
Inertia	The way matter resists any change in its motion. More mass means more inertia.
Force	A push or a pull, measured in newtons. One newton gives 1 kg an extra 1 m/s every second.
Acceleration	How quickly velocity changes, in m/s every second. Turning is acceleration too.
Momentum	Mass × velocity. Forces change it, and in any push between two things it is shared, never lost.
Impulse	Force × time, equal to the change in momentum. A longer stop needs a smaller force.
Action–reaction pair	Two equal and opposite forces that two objects exert on each other.
Centripetal force	The push towards the centre that keeps anything moving in a circle: m v² ÷ r.
Inertial frame	A point of view that isn't accelerating or spinning, where Newton's laws hold as written.

A short history

From Aristotle's 'everything needs a pusher' to a hammer and a feather falling side by side on the Moon: 2,300 years of working out why things move.

• 350 BCE · Everything needs a mover (Aristotle, Athens, Greece)
• 1638 · Balls rolling down ramps (Galileo Galilei, Published in Leiden, Dutch Republic)
• 1644 · Straight on, for ever (René Descartes, Amsterdam, Dutch Republic)
• 1687 · The Principia (Isaac Newton, with Edmond Halley, London, England)
• 1750 · F = ma becomes an equation (Leonhard Euler, Berlin)
• 1903 · The rocket equation (Konstantin Tsiolkovsky, Kaluga)
• 1948 · A unit called the newton (9th General Conference on Weights and Measures, Sèvres, near Paris)
• 1971 · A hammer and a feather on the Moon (David Scott, Apollo 15, Hadley–Apennine landing site, the Moon)

The full story, with 20 moments, charts, people and 26 sources: glassbox.how/e/newtonclear/history. The data lives in history.json.

Video and slides

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

Privacy

This box has no accounts and no ads, and it ships its own fonts and libraries. When you run it yourself it sends nothing anywhere. On glassbox.how, the site's /bar.js also loads Glassbox's analytics: Google Analytics to count visits (it asks first in the EU, UK and Switzerland, and stays off when your browser sends Global Privacy Control or Do Not Track) and ClickTrust to detect bots.

It remembers a few things in your own browser only, and never sends them anywhere:

Browser storage key	What it holds
newtonclear.v1	Which chapters you have opened, your best quiz scores, and sound on or off.

Exactly what each one sees is at glassbox.how/privacy.

Licences

• Code: MIT. Use it, change it, ship it.
• Explanations, text, images and videos (glassbox.json, glassbox/): CC BY 4.0. Credit “Glassbox, glassbox.how/e/newtonclear”.
• Third-party parts keep their own licences: three.js (MIT), Geist, Instrument Serif (SIL OFL 1.1).
• The Glassbox name and logo aren't covered by either licence. See the terms.

Found a mistake? Open an issue. Corrections happen in public.

Run it

It's plain HTML, CSS and JavaScript. No build step and no dependencies. Run locally, it contacts no other website.

python3 -m http.server 8000

Three.js and the fonts ship in vendor/ and fonts/, so it also works offline.

Then open http://localhost:8000.

How it's built

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/newton.js	Shared parts and physics: constants, chart boards, arrows that point anywhere, and simple models of a lab cart, people, a crash-test dummy, a car, a motorcycle, a bicycle and a desk fan
js/chapters/*.js	One file per chapter: the 3D model, controls, text, key terms, quiz and video scenes
glassbox.json	Title, question, explainer beats, key terms, browser storage and credits shown on glassbox.how
reel in each chapter	The storyboard the Glassbox studio records into short videos
glassbox/	The published video, slides, thumbnail and post copy
fonts/, vendor/three/	Self-hosted Geist and Instrument Serif (SIL OFL 1.1) and three.js (MIT)