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Equations of motion the conditions

  1. Jul 5, 2010 #1
    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. jcsd
  3. Jul 5, 2010 #2
    Re: Equations of motion!!! the conditions plzzz

    Small velocities compared to the speed of light and an inertial frame.
     
  4. Jul 5, 2010 #3
    Re: Equations of motion!!! the conditions plzzz

    Inertial frame ??? meaning wat ?
     
  5. Jul 5, 2010 #4
    Re: Equations of motion!!! the conditions plzzz

    Not rotating
     
  6. Jul 5, 2010 #5
    Re: Equations of motion!!! the conditions plzzz

    Uniform acceleration compensate the rotating phenomenon as well i think !!
     
  7. Jul 5, 2010 #6
  8. Jul 5, 2010 #7
    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.
     
  9. Jul 5, 2010 #8
    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.
     
  10. Jul 5, 2010 #9
    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
     
  11. Jul 5, 2010 #10
    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
  12. Jul 5, 2010 #11
    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.
     
  13. Jul 5, 2010 #12
    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.
     
  14. Jul 5, 2010 #13
    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.
     
  15. Jul 5, 2010 #14
    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.
     
  16. Jul 5, 2010 #15
    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.
     
  17. Jul 5, 2010 #16
    Re: Equations of motion!!! the conditions plzzz

    And I quote. From the OP.

    Inertial frame ??? meaning wat ?

    To which I answered 'not rotating'

    Simple question and direct answer.
     
  18. Jul 5, 2010 #17
    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'.

    Also, your answer is not correct, but that's not the topic of discussion in this thread
     
  19. Jul 5, 2010 #18

    HallsofIvy

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    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."
    to a question that asked only about the "equations of motion" and said nothing about relativity.
     
  20. Jul 5, 2010 #19
    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.
     
  21. Jul 5, 2010 #20
    Re: Equations of motion!!! the conditions plzzz

    Jeekeshan let me try to summarise.There are equations of linear motion and also equations of circular motion.The two sets of equations are analogous.I am assuming that you are referring to linear motion.The conditions necessary to use these equations is that the object must be moving in a straight line with uniform acceleration but I think you already know this.The equations break down as light speeds are approached so this places some limitations on their use.With equations of linear motion there are five quantities which are relevant and these are often given the symbols u,v,a,t and s.The symbols you use may be different.In order to solve a problem you need to be given three of the five quantities.Strangely,identifying what three quantities are given sometimes proves to be the most difficult part of the problem.First you need to identify the given quantities then select the right equation(s) to find the unknown(s) and then plug the numbers in.
     
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