Worksheet · Ages 8–11 · 30 min
Does gravity stop in space?
The misconception sheet. Children work out how strong gravity really is at the space station — about 88% of what it is in the classroom — and why astronauts float anyway.
Lots of books say astronauts float because there is no gravity in space. That is not true. Let us find out what is really going on.
- Earth is 6,371 km from its centre to the ground. The space station orbits 420 km above the ground.
- So the station is 6,371 + 420 = 6,791 km from the centre of the Earth.
- Gravity on the ground is 9.81. At the station it is 8.63.
- Work out: 8.63 ÷ 9.81 = ? Multiply your answer by 100 to get a percentage.
1. What percentage of Earth’s gravity is there at the space station?
2. So if there is still that much gravity, why do astronauts float?
3. When you jump off a step, are you weightless for a moment?
The station is falling, but it is also moving sideways at 27,600 km/h — so fast that the ground curves away beneath it as it falls. That is what an orbit is: falling and missing.
Write one sentence explaining to a friend why astronauts float. Do not use the words "no gravity".
For the grown-up
- This is the single most useful correction on the whole site. A child told "there is no gravity in space" has to unlearn it before orbits make any sense, and most of them are told exactly that.
- The sum is g = g₀ × (R ÷ (R + h))², which gives 8.63 m/s² at 420 km. Children do not need the formula — the division is the point.
- Watch for "because they are so far away". At 420 km the station is only about 6% further from Earth’s centre than the classroom floor is.
- The word scientists use is microgravity, not zero gravity, and the "micro" is honest: there are tiny accelerations aboard, roughly a millionth of surface gravity.
Every number on this sheet comes from: International Space Station