Gravity shapes orbits — Science, 14–17 years
An orbit is a continuous fall in which an object moves sideways fast enough to keep missing the body it is falling towards.
Falling around a planet
Gravity pulls an orbiting object towards a planet or star. The object also has sideways motion, so it keeps falling past the surface instead of hitting it. Its path curves because gravity continually changes the direction of its motion.
Why explain orbits?
The sky shows regular paths: moons, planets and artificial satellites do not simply move in straight lines. Gravity explains both the pull towards a large body and the curved paths we observe. This replaced the idea that orbiting objects need a constant push around a circle.
A satellite in low orbit
Imagine a satellite 400 km above Earth, moving sideways at about 7.7 km/s. Earth’s gravity pulls it downward, but during each second it travels far enough sideways that Earth’s curved surface falls away beneath it. The result is a repeated orbit, not hovering.
Orbiting is not floating
Astronauts in orbit look weightless, so it is reasonable to think gravity has disappeared. At the height of the International Space Station, gravity is still strong. Astronaut and station are falling together, and the station’s sideways speed keeps them continually missing Earth.
Satellites we rely on
Satellite orbits make navigation, weather forecasts and communications possible. Engineers choose an altitude and speed for the job: a low orbit gives detailed images, while a much higher geostationary orbit can stay above one region. Each choice has limits and costs.
Keep exploring
Other languages
Loading MyLeoNes™…