Gravity holds things in space — Astronomy, 7–10 years
Gravity is the pull between objects with mass. It makes things fall on Earth and helps moons and planets follow curved paths.
An invisible pull
Gravity is an invisible pull between objects. Earth pulls you towards its centre, which is why your feet stay on the ground. You also pull Earth, but Earth is so much heavier that its movement is too small to notice.
Why gravity matters
Without gravity, dropped objects would not fall, rain would not return to the ground and people could not stay on Earth. Astronomers also needed an explanation for why the Moon does not simply fly away. Gravity provides the pull, while motion carries the Moon forward.
A ball and the Earth
Throw a ball forwards. Step 1: your hand gives it forward speed. Step 2: Earth’s gravity pulls it down. Step 3: the ball follows a curved path and lands. A stronger throw makes it travel farther, but gravity keeps pulling down throughout its flight.
The no-gravity mistake
Astronauts in orbit look as if gravity has disappeared because they float. It is reasonable to think this, since nothing seems to pull them down. In fact, Earth’s gravity is still strong there; astronauts and their spacecraft are falling around Earth together, so they do not reach the ground.
Satellites and space travel
Gravity helps keep communication, weather and navigation satellites in orbit around Earth. Engineers choose a speed and height so a satellite keeps falling around the planet instead of crashing into it or escaping. The same idea helps plan spacecraft journeys, but real missions need careful calculations.
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