Eli5: why when I’m standing on a moving train and I jump, the train doesn’t move around me?
In: Physics
Velocity isn’t an absolute thing, you’re always moving relative to something else. Right now you assume you’re standing still, but in reality you’re only standing still relative to the earth. You’re actually moving at thousands of kilometers per hour relative to our solar system.
When you’re in a train it’s the same story. You’re standing still relative to the train, but you’re moving relative to the ground. A jump won’t affect your movement in the horizontal direction, according to the train you’re still standing still (albeit 20cm off the ground) and according to the ground you’re still moving. In order to start moving (relative to the train) you need to add some force in that direction, for example by walking or running.
Some confusion might come into play because of air resistance. If you’re watching a movie where some guy is standing on top of the train, jumps and flies off like the train is “moving away” below him, he’s actually being pushed off by the force of air slamming into him. If you’re inside a train this doesn’t apply.
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