# Homework Help: Proving 4 vectors!

1. Oct 21, 2013

### M. next

In books, it is always posted that velocity (dx$^{i}$/dt) is not a 4 vector. While du$^{i}$/ds and momentum are 4 vectors.. But it is never proved.

How to prove this?? I am not finding anyway to it.

You're my last hope!

2. Oct 21, 2013

### Simon Bridge

3. Oct 21, 2013

### M. next

Thank you for the reply, but can you tell me which one to use? I mean which formula from the two links?

4. Oct 21, 2013

### Simon Bridge

Do not apply formulas - test the properties of a 4-vector.
If you do not know how a 4-vector transforms, then learn and revisit the problem of a proof later.

5. Oct 21, 2013

### vanhees71

6. Oct 21, 2013

### M. next

Oh thank you! You mean that if I took the proper time and divided that by ds = cdt $\sqrt{1-(v^2/c^2)}$ I should get the 4 components of U. And I say that yes, these looks like (dA^0, dA^1, dA^2, dA^3) as in your link so it is a 4 vector. Right?

7. Oct 21, 2013

### M. next

sorry I meant if I took Ui and divided that by ..