# [ELI5]How do we move relative to a bus when we jump in one?

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[ELI5]How do we move relative to a bus when we jump in one?

In: Physics

In an idealized scenario, you don’t. The bus, the air inside it, and you are all moving at the same speed, with no velocity relative to each other. So, you jump up and come back down in the same spot.

Now, of course, from the frame of reference of someone standing on the side of the road, you’re moving at the same rate as the bus.

To add to what /u/ToxiClay correctly explained above, the only way you will move relative to the bus is if the bus accelerates or brakes while you are in the air.

Here is an absolutely fantastic demonstration of the fact that you *do not* move relative to a vehicle you jump in: [a guy on a trampoline being pulled by a truck](https://www.youtube.com/watch?v=zeqMsf66-mY)!

Wrong question. You don’t when it’s moving at a constant velocity.

When the bus is ***accelerating*** is when you move relative to it.

And for that, you don’t have to jump. A hard pick up will slide your ass back or a hard braking will smash your face forward even when you’re sitting down. Why?

Newton’s first law: it doesn’t take anything to keep you at a constant speed, be it 0 mph or 10,000 mph.

But to change it, **force** is required.

The force the Earth puts on the tyre, the tyre on the axle, the axle on the frame, the frame on the floor, the floor/seat on your feet/butt and your feet/butt on the rest of you.

And if it doesn’t, you go flying through the windshield.