Science labs › Earth and space › Orbital Mechanics
Newton's cannonball: how fast must you fire it sideways so it never lands?
Orbital Mechanics lab · Last updated: 16 October 2026
You fire a cannonball sideways from a mountain top, as Isaac Newton once imagined, and keep firing it faster. Slow shots crash nearby, faster ones land further away, and at the right speed the ball falls all the way round Earth without ever landing. That is exactly how satellites and the Moon stay in orbit.
What you'll discover
- Anything thrown sideways falls towards Earth, but the faster it goes, the further it travels before landing.
- Earth's surface curves away beneath a fast enough object, so it keeps falling but never reaches the ground.
- An orbit is a never-ending fall: astronauts float because they and their spacecraft are falling together.
The science in plain words
Isaac Newton imagined a cannon on a very tall mountain, firing a ball sideways. Gravity pulls the ball down the moment it leaves the barrel, so it follows a curved path to the ground. Fire it faster and it lands further away. Because Earth is round, the ground curves away beneath the ball, so a fast enough ball travels a long way before it meets the surface.
At one particular speed the ground curves away exactly as fast as the ball falls. The ball keeps falling but never gets any closer to the ground, so it circles Earth for ever. That is an orbit. Close to Earth's surface, ignoring air, this speed is about 7.9 kilometres per second, roughly 28,000 kilometres per hour. Go a little faster and the orbit becomes a stretched ellipse. At about 11.2 kilometres per second the ball escapes Earth altogether.
Satellites, the International Space Station and the Moon all orbit this way. They are not beyond gravity: at the space station's height gravity is still about nine tenths as strong as on the ground. Astronauts float because they and their station are falling together, so nothing pushes against them. Real satellites are launched above most of the air, because air resistance would slow them down.
Where it fits
- India, NCERT: Class 9 science, Chapter 9: Gravitation
- United States: Grades 6 to 12
- Next Generation Science Standards: MS-ESS1-2, HS-ESS1-4
Common questions
How do satellites stay in orbit?
A satellite is always falling towards Earth, but it also moves sideways very fast. As it falls, Earth's surface curves away beneath it at the same rate, so it never gets closer to the ground. Gravity keeps bending its path into a loop round the planet.
Is there no gravity in space?
There is plenty of gravity in space. At the height of the International Space Station, gravity is about nine tenths as strong as on the ground. Astronauts float because they and the station are falling round Earth together, so they feel weightless.
How fast does something need to go to orbit Earth?
Just above Earth's surface, ignoring air, an object would need to travel about 7.9 kilometres per second, roughly 28,000 kilometres per hour, to stay in orbit. Higher orbits need less speed. To escape Earth completely, an object needs about 11.2 kilometres per second.
Related labs
- Projectile Launcher: Aim the launcher and fire a marble. Which angle sends it furthest?
- Solar System: A desk orrery run by real gravity: why does Mars take longer than Earth to go round?
- Roundabout Ride: Spin the roundabout. How hard must the spring pull to keep the toy going round?
See all earth and space labs or every Taz science lab.
Try it yourself
The Orbital Mechanics lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.