Orbits and Satellites
Satellites fall around Earth while moving sideways fast enough to miss it.
About this topic
A satellite is in constant free fall around Earth, moving sideways fast enough that the ground curves away beneath it as it falls. Gravity provides the centripetal force, so GMm/r² = mv²/r, giving v = √(GM/r). Higher orbits are slower and longer. This is the key to understanding why satellites stay up without engines.
Low Earth orbit speed is about 7.8 km/s, giving a period of roughly 90 minutes, so astronauts on the space station see about 16 sunrises a day. A geostationary orbit, at about 36,000 km altitude, has a period of exactly 24 hours, so the satellite hovers over one spot on the equator. Newton imagined this with a cannon on a mountain: fire faster and faster and the cannonball lands further away until it never lands.
Worked example: for orbit radius r the speed does not depend on the satellite's mass, so a tiny cubesat and a huge station at the same height move at the same speed. To catch up with something ahead of you in orbit you must slow down, drop to a lower faster orbit, and then rise again.
Applications include GPS, weather forecasting, television, telephone links and Earth imaging. A common misconception is that there is no gravity up there. There is plenty; orbiting objects simply keep missing the ground.
Key ideas
- Orbital speed v = √(GM/r)
- Higher orbits are slower
- Geostationary orbit matches Earth's spin
Quick check
Use cases: where Orbits and Satellites helps
- Homework: review the key idea behind Orbits and Satellites before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Orbits and Satellites without notes.
- Visual learning: play with the interactive lab to see how Orbits and Satellites changes when you adjust its inputs.
- Teaching a friend: explain Orbits and Satellites in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Orbits and Satellites?
Satellites fall around Earth while moving sideways fast enough to miss it.
What will I learn in Orbits and Satellites?
Orbital speed v = √(GM/r). Higher orbits are slower. Geostationary orbit matches Earth's spin.
Is Orbits and Satellites part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Orbits and Satellites lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Orbits and Satellites?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.