# Equations of motion the conditions

1. Jul 5, 2010

### jeekeshen

Equations of motion!!! the conditions plzzz

What are the conditions that enable the equations of motion to be used except from the fact that acceleration must be uniform ???

2. Jul 5, 2010

### bp_psy

Re: Equations of motion!!! the conditions plzzz

Small velocities compared to the speed of light and an inertial frame.

3. Jul 5, 2010

### jeekeshen

Re: Equations of motion!!! the conditions plzzz

Inertial frame ??? meaning wat ?

4. Jul 5, 2010

### AJ Bentley

Re: Equations of motion!!! the conditions plzzz

Not rotating

5. Jul 5, 2010

### jeekeshen

Re: Equations of motion!!! the conditions plzzz

Uniform acceleration compensate the rotating phenomenon as well i think !!

6. Jul 5, 2010

7. Jul 5, 2010

### AJ Bentley

Re: Equations of motion!!! the conditions plzzz

If you sit in a train travelling at steady speed (inertial frame) and toss a ball to a friend he can catch it - no problem.

If you both are on a ship in a storm, wildly, suddenly changing direction OR you both sit on a children's 'roundabout' while it's spinning (both non-inertial frames) you will find it nearly impossible. The laws of motion for the non-inertial frame will be different from those you are used to.

You may be able to compensate by adding in some complicated motion of your own - but that isn't the point.

8. Jul 5, 2010

### Dickfore

Re: Equations of motion!!! the conditions plzzz

@OP:

I think you meant to ask about initial conditions. You still need to know the initial position and the initial velocity of the particle.

9. Jul 5, 2010

### jeekeshen

Re: Equations of motion!!! the conditions plzzz

ya thats wat i meant the initial conditions :S.. just like acceleration should be uniform, many questions ask too but the other one that speed must be less than speed of light is too obvious else the matter will disintegrate :S

10. Jul 5, 2010

### bp_psy

Re: Equations of motion!!! the conditions plzzz

No,what I meant is that the velocity of the object must be significantly smaller then the velocity of light for the Newtonian equations of motion to work. At velocities that are a significant fraction of c, those equations do not work due to relativistic effects.There is also no reason for matter to disintegrate at speeds close to c.

Last edited: Jul 5, 2010
11. Jul 5, 2010

### AJ Bentley

Re: Equations of motion!!! the conditions plzzz

No he didn't (now he thinks he does!) He barely speaks English - doesn't understand what you mean - you just confused him.

12. Jul 5, 2010

### Dickfore

Re: Equations of motion!!! the conditions plzzz

Lol, I confused him and not you with talks about non-inertial reference frames and speed of light.

13. Jul 5, 2010

### AJ Bentley

Re: Equations of motion!!! the conditions plzzz

Look to see who's saying what before you post. I never mentioned either except to explain in detail what a non-inertial frame is.

14. Jul 5, 2010

### bp_psy

Re: Equations of motion!!! the conditions plzzz

:rofl:
I am sorry If I confused him. I consider that position and velocity are info necessary to using the equations not something that restrains their validity.That is what I thought he was asking.

Yeah blame poor old bp.

15. Jul 5, 2010

### Dickfore

Re: Equations of motion!!! the conditions plzzz

Who asked you to explain anything? You assumed that this is the question he was asking and proceeded with your own answer. This is the same thing I did. So, please, don't tell me what he meant or he didn't mean.

16. Jul 5, 2010

### AJ Bentley

Re: Equations of motion!!! the conditions plzzz

And I quote. From the OP.

Inertial frame ??? meaning wat ?

To which I answered 'not rotating'

17. Jul 5, 2010

### Dickfore

Re: Equations of motion!!! the conditions plzzz

Do you mean the original poster or the original post when you say OP? It is obvious he was confused as hell by that point so he used 'wat'.

18. Jul 5, 2010

### HallsofIvy

Re: Equations of motion!!! the conditions plzzz

But he only asked that in response to bp-psy's response
"Small velocities compared to the speed of light and an inertial frame."

19. Jul 5, 2010

### bp_psy

Re: Equations of motion!!! the conditions plzzz

He said nothing about relativity but he didn't specifically asked to ignore it.I think that my answer was valid considering how the question was formulated. Anyway feel free to delete all posts up to the op since I see this thread got ugly.

20. Jul 5, 2010