Why Do You Move Backwards When Jumping Inside an Accelerating Bus?

[stop1it]

Does Jumping on a bus such that you are not touching any part of the bus (i.e. only the air inside the bus), when the bus is accelerating forward, result in you moving backward relative to the bus (due to inertia)?

If yes, why isn't it the same when you are jumping on the Earth? If no, why not?

Elaborate Answer needed. [out of curiousity]

 

[Vyse007]

You shouldn't be moving backward relative to the bus, simply because your body is not in contact with the floor of the bus. Recall that inertia acts on passengers in the bus who are sitting or standing in the bus. That is because some part of their body is in contact with the bus, which is moving relative to earth. So when it suddenly stops or accelerates faster, the inertia of the upper body tries to stay at rest, thereby resulting in the jerk.
Not sure I completely get your question, but I hope its what I think it is. :-)

 

[Mentallic]

Does Jumping on a bus such that you are not touching any part of the bus (i.e. only the air inside the bus), when the bus is accelerating forward, result in you moving backward relative to the bus (due to inertia)?

Yes, definitely. But considering that a jump of 30cm high will only result in a jump that lasts a quarter of a second, you won't notice much. You would need to time it quite well, so if you ever see the lights ahead turning orange and the bus is in a position that you need to floor the brake, it's the best time to jump

In a more simple scenario, we can stop time at the moment you are in the air, by removing gravity. In a spaceship bus, of course you will move relative to the bus if it accelerates.

If yes, why isn't it the same when you are jumping on the Earth? If no, why not?

The centripetal accelerations due to the Earth's orbit are minute compared to the strength of gravity. Your trajectory on an Earth that neither orbits the sun nor rotates will be very slightly different to the way it is now. These tiny differences do add up however, and such examples are of the http://en.wikipedia.org/wiki/Foucault_pendulum"