World
What If Everyone Jumped?
If everyone on Earth jumped at once, would the planet notice?
Conservation of momentum does not care about feelings. If eight billion people push down on the ground together, Earth is pushed the other way by the same impulse. Earth's mass is about 6 × 10²⁴ kilograms, so the recoil speed is not a rounding error in a poetic sense — it is a rounding error in a literal one, something like 10⁻¹³ metres per second. While everyone is in the air, the planet has that tiny delta-v. When they land, they hand the momentum back. Net displacement of Earth's orbit is not a thing this experiment will claim. The interesting number is how small a planet makes a crowd.
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About 8 billion is a current world population ballpark.
Your result
2.01 × 10^−13
Earth's peak recoil speed (m/s)
while everyone is airborne
- Takeoff speed
- 2.43 m/s
- Momentum of the crowd
- 1.20 × 10^12 kg m/s
- Earth recoil Δv
- 2.01 × 10^−13 m/s
- Kinetic energy of the jumps
- 1.46 × 10^12 J
- After they land
- net Δv ~ 0
- Earth mass in the model
- 5.97 × 10^24 kg
What does that mean?
While 8,000,000,000 people of 62 kg are in the air after a 0.3 m hop, Earth recoils at 2.01 × 10^−13 m/s. That is not a typo in the exponent. Hang time is about 0.49 s; then they land and the impulse reverses. Net change in Earth's orbit: about zero. The people were already part of the planet. A jump is a brief internal rearrangement, not a rocket.
At a glance
- Crowd mass4.96 × 10^11 kg
- Earth mass5.97 × 10^24 kg
Compare
| Airborne | 2.01 × 10^−13 m/s recoil | |
|---|---|---|
| Back on the ground | ~0 net | momentum returned |
| Earth's orbit | not shifted by a hop |
Compare scenarios
A jump is a brief loan of momentum
Takeoff speed for a hop of height h is sqrt(2gh). Multiply by the number of people and their mass and you have a momentum. Divide by Earth's mass and you have a recoil. The formula is the same one that makes a rowing boat nudge backward when you step onto the dock, written at planetary scale. No, the planet does not 'shift in its orbit' in any lasting way. Orbits care about the centre of mass of Earth-plus-people, which barely moved because the people were already standing on Earth.
Landing closes the books
While the crowd is airborne, Earth has a whisper of opposite velocity. Contact on landing applies the opposite impulse (plus a bit of heat and sound). After everyone is standing again, the Earth–crowd system has the same total momentum it started with, ignoring the millimetre of extra height they no longer have. If you want a lasting change in Earth's motion, you need to throw mass into space or rearrange it permanently. A jump is neither.
Energy is a crowd, still not a quake
Kinetic energy at takeoff is ½ N m v². For eight billion people that can look like a large joule count because there are many of them, not because any one patch of crust was loaded like a bomb. The energy is spread across every inhabited place at once. This page will show the joules and refuse to translate them into a fake earthquake magnitude. Magnitude is a local seismic measurement. A coordinated hop is not one.
How we calculated this
Takeoff speed is sqrt(2 g h) with g = 9.80665 m/s². Recoil uses physics.earthJumpRecoil: momentum N m v against Earth's mass from the NASA fact sheet. Delta-v is that ratio. Energy is ½ N m v². After landing, net delta-v is treated as zero. People are a number slider, not a geographic map, so there is no crustal loading model and no seismic magnitude.
Go further
A curated rabbit hole from this question. Each link is a real experiment, not a random suggestion.
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