Physics · Chapter 03
🌍 Gravity
Why things fall and orbits happen.
💡 Why Things Fall
Gravity is the invisible force that pulls everything towards the centre of the Earth. Drop a ball — gravity yanks it down at 9.8 m/s². Every second, it falls 9.8 m/s faster.
Two objects, dropped together in a vacuum (no air), land at the same time — feather or hammer. Galileo proved this. Astronaut David Scott reproduced it on the Moon. 🌙
The pull also keeps the Moon orbiting Earth, and the Earth orbiting the Sun. Gravity is what holds the universe together.
F = G × m₁ × m₂ ÷ r²
Apollo 15 — feather and hammer fall together on Moon (no air resistance)NASA / Public Domain
Bay of Fundy tides — caused by Moon's gravitational pullWikimedia Commons / CC BY-SA 3.0
🎬
Drop the Apple 🍎
AnimationApple falls. Velocity increases every moment because of gravity's pull (g = 9.8 m/s²).
🧪
Change the Planet
ExperimentDrop the apple on different planets. Notice how gravity changes the fall speed.
20 m
Time to fall (√(2h/g))2.02 s
Impact velocity19.8 m/s