Eli5: why when I’m standing on a moving train and I jump, the train doesn’t move around me?
In: Physics
The train gives you its forward motion after you climb aboard and it starts moving. Everything in the train, you, other people, the luggage, the air, everything is moving forward at the same speed as the train.
Things in motion tend to stay in motion unless there’s some force acting upon them. Friction, or actually being pushed, etc.
So if you were to jump straight up, and at that moment the train slammed the brakes for some reason, the train would slow down abruptly, but you would still have the same motion as before, because while you’re airborne (from the jump) only the force of gravity affects you, and gravity pulls straight down, not sideways.
So you would see the train suddenly stop, and a camera bolted to the train would record you suddenly moving forward.
This is why they have seatbelts in cars. You’re going at the same speed as the car, but if the car hits something, IT would suddenly stop, but you’d be still [going forward at the same speed](https://youtu.be/YLCWGcNpY94?t=76), and basically hit the front of the cabin and/or with possibly enough force to be thrown through the window.
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