# Clocks on spaceship travelling at the speed of light

1. Nov 8, 2007

### physics2460

1. The problem statement, all variables and given/known data

Hi guys, I'm in a Physics for poets class? Could you , please, help me with these questions?

Suppose you are watching a spaceship go past you toward the right at close to the speed of light.

1. How do the clocks on the spaceship appear to run compared to your own clock?
2. If you could measure the length, depth and height of the spaceship, how would each of these change compared to your measurement when the ship is stationary?
3. How would a passenger on the spaceship observe your clock runs? How would the passenger claim you height, depth, and length would change?

2. Relevant equations

3. The attempt at a solution

Last edited: Nov 8, 2007
2. Nov 8, 2007

### DaveC426913

I see you took the time to form the post according to guidelines. Were you planning on filling any of those sections in? Fer instance #3?

3. Nov 9, 2007

### Bill Foster

They appear to run slower than your own clock...

$$\Delta{t}=\frac{\Delta{t_0}}{\sqrt{1-\frac{v^2}{c^2}}}$$

Assuming length is in the x direction and assuming the ship is moving in the x direction...length will appear shorter and both height and depth will appear normal.

To the passenger, your clock will be running slower, and your length will be compressed.

This explains it: http://en.wikipedia.org/wiki/Special_relativity

4. Nov 9, 2007

### DaveC426913

PF has a policy of not spoon feeding people with answers for homework. It is required to show one's attempts first. And even then, they are guided towards the answer, not handed it.

5. Nov 10, 2007

### physics2460

Dear DaveC426913,

I don't understand why it bothers you so much, or maybe I do understand a little. I've been doing fine in my physics class and had lots of success on my weekly quizes. But it's the end of the semester and I thought I was lucky I found you, guys, because, sometimes it's simply not possible to cover all of the homewhork material (not only physics)Do you have any idea how helpfil Bill Foster's answer will be when I actually will sit down with my book and try to make sense out of my Chapter 9 and the assignment I was given. All I'm saying, don't overpolice us. We are good students and don't just want answers on a china plate with a blue ribbon brought to us, but it does help when someone is just being kind and without asking too many questions and posing too many demands just kindly gives us a hand. If we didn't want to succeed we would not be here in the first place.

Dina

6. Nov 10, 2007

### physics2460

clocks on the ship question

Bill I apprecialte your help so much,

Thanks,
Dina

7. Nov 10, 2007

### DaveC426913

It doesn't bother me at all. It's forum policy, and it's there for a reason.

Nobody here is going to leave you floundering without any answer, but the whole point of being in school is that YOU learn by trying. You didn't try. Now, when you go to do your work, you won't have to go through the brain-stretching process of formulating your own ideas and thinking them through.

Though you may not think so now, I am not being unkind, I am helping you learn, which is what you're here for.

8. Nov 12, 2007

### dynamicsolo

And this is certainly the chief reason for running this forum this way. People only really learn by struggling with problems in search of solutions; this in fact leads to actual physical changes in the brain, which are retained. This process does not appear to take place passively, but only by dint of effort of the individual. (Believe me, I've worked directly with enough students by now to see this in action...)

But there is a simple practical reason for not running this forum as a "drop-off" service for problem solutions. Being on the Internet, this place would be instantly and steadily flooded with thousands of posts a day, all wanting delivery of answers! (I'm currently grading homework for an instructor who only assigns odd-numbered problems from a book for which the solution manual is available -- guess what happens...) We are happy to offer guidance and assistance, but an attempt at a solution has to be the price of admission...

9. Nov 12, 2007

### physics2460

I totally agree with you, guys. But I think we should let it go. It was the only question that I ever asked on the forum since the beginning of the semester. I did pretty well learning that far on my own. Thanks for the answer and the advice.

However, Dave's condescending tone was totally inappropriate here. That's how I feel.

10. Nov 12, 2007

### DaveC426913

It's just that you took the time to read the guidelines, and posted in the correct format and all.

Anyway, hope this isn't the last you post here. Not everyone here is a jerk like that Dave guy.

11. Nov 12, 2007

### cristo

Staff Emeritus
If you hang around the homework forums for long enough, you will realise that there are a lot of people who try and get help on a homework question without showing work. This is again PF rules as Dave has mentioned. I'm sure Dave didn't mean to be condescending; you should note that there are only a finite number of ways one can say "so.. what do you think?" or "have you had a go at the questions yourself?" I don't see Dave's response as anything different to those other ways of saying the same thing.