1. Apr 5, 2009

### DWill

1. The problem statement, all variables and given/known data
1) You are gliding over Earth's surface at a high speed, carrying your high-precision clock. At points X and Y on the ground are similar clocks, synchronized in the ground frame of reference. As you pass over clock X, it and your clock both read 0. (a) According to you, do clocks X and Y advance slower or faster than yours? (b) When you pass over clock Y, does it read the same time, an earlier time, or a later time than yours?

2) You are floating in space when you notice a flying saucer circling you. Each time it passes in front of you, you note the reading on its clock. Do you see its clock advancing faster or slower than your wristwatch? Does the space alien see your watch advancing faster or slower than his clock? Explain.

2. Relevant equations

3. The attempt at a solution
I just started learning about relativity in class, so I was just wondering if my thinking is correct so far.

1) (a) The inertial frame is your own frame, because events happen at the same location in that frame right? I think that means time would advance slower in the other frame, so clocks X and Y would advance slower.
(b) If X and Y advance slower, it would read an earlier time right?

2) The inertial frame here is the space alien's frame, because events happen at same location in that frame. Therefore you would see its clock advancing faster than yours. I'm not sure about the 2nd part of this question, wouldn't yours just seem slower to the alien?

Thanks

2. Apr 6, 2009

### tiny-tim

Hi DWill!

1) The concept of "because events happen at same location in that frame" is strictly correct, but it's much easier to think "an inertial observer always regards other clocks as going slower".

Your (a) and (b) are correct.

2) Again you've tried to apply "because events happen at same location in that frame" … but I've no idea why you think that applies to one frame rather than the other.

Try again, with "an inertial observer always regards other clocks as going slower".

3. Apr 6, 2009

### DWill

Thanks tiny-tim for the reply, but I'm a little confused on what you said on how to figure out which is the inertial frame. How do you know in which one the clocks go slower?

4. Apr 7, 2009

### tiny-tim

An inertial observer or an inertial frame is one that has uniform velocity (ie, a fixed speed in a fixed direction), and isn't rotating.