Satellite Orbit Lab: Why the Space Station Never Falls Down
Use Newton’s cannon to see that a satellite is always falling; it stays up because it moves sideways so fast that the curved Earth drops away beneath it. Astronauts float because they fall with their station.
Before you try
What if gravity switched off for the space station? Would it stay in place or fly away?
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What happened?
Move a control to see what changes and why.
Earth alone and no air; a real launch climbs through the atmosphere first and then tips over to gain sideways speed.
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Try these ideas
- At 400 km press Circular speed and launch. Then knock 0.5 km/s off and launch again.
- Press Escape speed and watch the path open out.
- Raise the height to 2,000 km. Do the circular and escape speeds go up or down?
Why it works
Gravity at the height of the International Space Station, 400 km up, is still about 89% as strong as on the ground. The station is falling the whole time. It never hits the ground because it also moves sideways at 7.7 km/s, and in the time it falls a little, the round Earth has curved away by the same amount. That is what an orbit is: falling forever and always missing.
This lab recreates Newton’s thought experiment. A projectile fired horizontally from a tall mountain is followed under gravity that weakens with distance. Below the circular speed it lands; at the circular speed it orbits in a circle; between that and the escape speed it makes an ellipse; at the escape speed it never returns. The readouts give the exact speeds for your chosen height.
Check your understanding
Question 1 of 4
Why do astronauts on the space station float?
A satellite launched sideways at less than the circular speed will
Escape speed compared with circular speed at the same height is
The ISS orbits in about
Explain it in your own words
What changed? Why did it happen? Where might you notice this in everyday life?
For parents & teachers
- Swing a ball on a string and ask what happens if the string breaks.
- Ask: why do geostationary satellites stay over one spot?
- Look up when the ISS passes over your town and go and see it.