# Can I really not tell if I am in motion?

1. Jul 31, 2009

### Nanyang

Sorry! I think I figured the mistake out right after I posted! This thread can be closed.

A region of hotter temperature evaporates some water and turn the wheels, and the evaporated water is at a lower temperature.

So I am in the train and I observe that the engine works in the way described above. Relative to myself, I claim that I am not the one in motion but the station platform is in motion.

But to claim that the station platform is in motion I must also claim that the wheel turns in the other way (edit: sorry, mistake here. give me a moment to sort this out). This implies that the evaporated water must fall back into its liquid form from a colder temperature to a hotter temperature. But by the second law of thermodynamics, this is impossible. So I must conclude that I am the one in motion and not the platform despite measuring in my own frame of reference.

So, can I really not tell if I am in motion?

Last edited: Jul 31, 2009
2. Jul 31, 2009

### maverick_starstrider

You're forgetting that the reason the wheels have to turn in the first place is because friction slows the train down and the engine needs to compensate by providing a constant acceleration.