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This Quick Question explains the difference between gravity and g-force, and how you can experience zero-g in space even when it’s not zero gravity!
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Zero G, a phrase that people use all the time to describe the phenomenon of perceived weightlessness. Usually in space. But zero G does not mean zero gravity because there's gravity everywhere. If there were truly no gravity in space, planets and stars wouldn't even form, let alone orbit around each other.    So gravity is a thing, everywhere all over. But we sometimes refer to the effects of gravity in a specific way as G-force. Despite its name, not only is it not a measurement of gravity, it's not a measurement of force either. It's a unit of acceleration, and that acceleration is usually caused by gravity.   Officially, one G is the acceleration of an object caused by gravity near the surface of the Earth. So you know, you throw your phone out your window, you jump up into the air or drop your keys on the street, they fall at the same rate. About 9.8 meters per second squared. That is known as standard gravity.   Now 2G of course would just be double that. You could experience that much acceleration if you are speeding away from the Earth in a spacecraft or in a drag racer that is blasted from zero to 160 kilometers per hour. In those situations, you experience G-force as a sensation of weight.    As you hurtle along in your spaceship or your dragster, you'd be pulled back into your seat, and if there were a bathroom scale behind you, it would register those G-forces.   But where you can't experience weight, you can't experience G-force. And this is what happens to astronauts in space. When they orbit Earth, they are in a state of constant free-fall. Basically they are continually falling toward Earth but missing it and then falling toward it some more.   So even though they are very much under the influence of gravity, they aren't experiencing G-force. So we call that environment zero G, even though, confusingly enough, it is not the same thing as zero gravity.    We should probably have come up with a better name, but it is too late for that now.    Thanks for asking, and thanks to our Subbable subscribers who keep these answers coming and get the questions a little bit before everybody else.   If you have a Quick Question, you can let us know on Facebook or Twitter or Tumblr or down in the comments below. And don't forget to go to youtube.com/scishow and subscribe.