# What is relative or absolute?

1. Oct 25, 2009

### Shahin.Omar

Hello!

Can someone explain to me what is relative, and what is non-relative or absolute?
As I understand linear motion at constant velocity is called relative.
Can you give more such examles for me to understand why something is called relative?

Cheers!

2. Oct 25, 2009

### rcgldr

Position and velocity are relative to some frame of reference. Acceleration and related forces can be considered to be absolute if not considering general relativity issues.

Getting back to position and velocity, say you're standing at some spot on the earth. The earth is rotating, so except at the poles, it's surface is moving (with respect to it's own axis), the earth is orbiting the sun, the sun is orbiting the center of our galaxy, and our galaxy is moving with respect to others.

3. Oct 25, 2009

### Shahin.Omar

Please can you exlain it a little bit more, and what is accepted in physics today?

Is rotation of earth on its axis relative?

And can I define 'relative' as an event/attribute that requires a frame of reference for it to be detected?

:)

Last edited: Oct 25, 2009
4. Oct 25, 2009

### A.T.

You can express rotation relative to something. But you can also quantify rotation's absolute value, which doesn't work for linear motion at constant velocity.

5. Oct 25, 2009

### Shahin.Omar

Whats rotation's absolute value, how do I quantify it?
Can you help me define relative and absolute so I can tell what is relative and what is not?

6. Oct 25, 2009

### Shahin.Omar

Just to add, the definitions required is for bodies *not* approaching the speed of light.

Last edited: Oct 26, 2009
7. Oct 25, 2009

### A.T.

You can measure the inertial forces and calculate the rate of rotation from it.
Relative means it was compared to some arbitrary reference. Absolute means no arbitrary reference was used.

8. Oct 26, 2009

### Shahin.Omar

Can you also tell me the exact extent to which the above definitions are correct (apart from the term I used)?

9. Oct 26, 2009

### A.T.

Can you ask a physically relevant question?

10. Oct 26, 2009

### Shahin.Omar

Sorry for any ambiguity!

What I wanted to know is if the definitions you gave are universally accepted by all theories (like Quantum Mechanics and General Relativity) or they are only correct from Classical Mechanics point of view?

If it is only accepted in classical mechanics, can you tell me what is the accepted definition in GR or QM?

Hope this clarifies any doubts.

:)

11. Oct 26, 2009

### Shahin.Omar

12. Nov 6, 2009

### Shahin.Omar

I have not had a final reply to this thread, I did not form my question correctly in the beginning, not that it was easy, sometimes you don't know how to put it?

I would like to close this thread with final conclusion; while we can quantify what is relative we cannot quantify what is absolute, if we could quantify what is absolute there would no difference between relative and absolute.

A.T. was wrong in saying, "But you can also quantify rotation's absolute value."

Cheers guys!

13. Nov 6, 2009

### D H

Staff Emeritus
The only one who is wrong here is you, Shahin.

14. Nov 6, 2009

### Shahin.Omar

No problem, except you cannot prove it. Be happyy!

Cheers!

Last edited: Nov 6, 2009
15. Nov 7, 2009