# B Newbie question -- A train in space with a ball floating in a train car...

1. Jun 12, 2017

### Nyloth

Hello, I am someone who has no experience in physics other than primary/highschool and I have a quick simple question about something I cant wrap my mind around as a complete physics newbie. Please have understanding.

The question: lets say a train is standing still at a point in space (so there is no forces like gravity acting on it). One of the vagons is completelly vacuumed and in the center of that vagon a ball is floating, standing still at its center, not touching any of the vagon's walls. The train begins moving forward in a straight line. What happens to the ball at the center of the vacuumed vagon? Does it remain in that exact place untill it is hit by a vagon wall (so that it is completely unnaffected by the trains movement) or does it begin moving with the vagon and only slowly approach the wall opposite wall due to the acelleration? Thank you

2. Jun 12, 2017

### rumborak

As there are no forces acting on that ball, indeed it will stand still (until the wagon wall eventually hits it).

3. Jun 12, 2017

### Staff: Mentor

With no forces being applied to the ball, it will remain motionless with respect to the original frame of reference while the train accelerates around it....until the back wall of the train car collides with it.

4. Jun 12, 2017

### Nyloth

Why is this not the same for light? For example if a train is moving with speed of light in a straight line, why would light need to catch up with the front wall of the vacuumed vagon at the speed of light and illuminate the whole vagon? Again, i am a newbie and i know im missing important premises here and the way i formulared this question is faulty but hey it doesnt hurt to ask.

5. Jun 12, 2017

### Staff: Mentor

I don't see what this has to do with your first question/scenario. Every bit of it is different except that it involves a train. So please define this new scenario more specifically before asking a question about it - I don't understand what the scenario is, what you think is supposed to be happening or why.

That said, note that trains cannot travel at the speed of light, even in theory.

6. Jun 12, 2017

### Mister T

Light is never motionless. Therefore a train can't travel at light speed.