Gravitational fields and orbits — Physics, 14–17 years
A gravitational field describes how masses attract, from a falling apple to a spacecraft circling Earth.
The idea
A gravitational field is the region where a mass would feel a gravitational pull. Near Earth, the field points towards Earth and has about 9.8 N/kg. An orbit is not a place without gravity: it is continuous falling while moving sideways fast enough to keep missing the ground.
Why it matters
Saying that Earth pulls an object explains one event, but a field lets us describe the pull at every position around Earth or another mass. This solved the problem of predicting falling objects, planets and moons with one model. It came from Newton’s attempt to connect falling bodies with orbital motion.
Worked example
A 4 kg object is near Earth, where the gravitational field strength is 9.8 N/kg. Its weight is mass × field strength: 4 × 9.8 = 39.2 N. The force points downward, towards Earth. If the same object were on the Moon, its mass would stay 4 kg but its weight would be smaller.
The common trap
People often say astronauts in orbit have no gravity because they look weightless. That is a reasonable conclusion from what they see, but gravity is still pulling them towards Earth. They float because the spacecraft and astronauts are falling together, not because the field has vanished.
Where it appears
Satellites use carefully chosen orbits to provide maps, weather images, navigation and communication. Engineers calculate the field and the satellite’s speed so it keeps circling instead of falling into the atmosphere or escaping into space. Different jobs need different orbital heights and periods.
Keep exploring
Other languages
Loading MyLeoNes™…