# Q & A: Everybody Jump!

Q:
If everyone on earth jumped up in the air at the same time would the weight of the earth change?
- shane stewart (age 30)
A:
Shane -

No, if everybody on the earth were to jump all at once, the weight of the earth (really, its 'mass') would not change. The earth's mass is determined based on how hard its gravity pulls on things - for instance, the force of Earth's gravity on the moon or on you. (More mass means more gravity.)

Because of this, the earth's mass does include the mass of all of the people, plants, and animals that live here. This is because all objects have gravity, no matter how small they are (although very light objects don't produce very much gravity at all). So the gravity that you feel pulling you down really comes from the earth plus all of the people on it. Even if everyone were to jump up into the air, they would still produce gravity that pulls on everyone and everything else. There would be a little change in the force on things right near the Earth's surface, because a little part of the mass would be briefly in new locations, but the total mass as seen by, say, the Moon wouldn't change.

If everybody were to leave the earth and go to say, Neptune, then the mass of the earth would be a little bit less than it is now, since other objects would feel a little bit less gravity from it. But the difference would be really tiny, since even the earth's entire population weighs hardly anything compared to the rest of the planet.

-Tamara

(published on 10/22/2007)