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What is necessary for an object to move?

  1. Feb 1, 2012 #1
    Quick question, what is necessary for an object to move?

    I want to say mass & velocity but is there anything else?
  2. jcsd
  3. Feb 1, 2012 #2


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    Staff: Mentor

    Welcome to the PF.

    What is the context of the question? What course is this for? What have you learned so far about Newton's Laws?
  4. Feb 1, 2012 #3


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    Science Advisor

    Strange question! If an object has non-zero velocity, relative to some frame of reference then it is moving in the frame of reference. That does not require "mass" unless you are requiring mass in order to qualify as an "object".
  5. Feb 1, 2012 #4
    I'm in physics and it's a question on my midterm review sheet that has Newton's Laws, Forces, Inertia, Free Body Diagrams, Weight, Gravitation and Friction on it.

    Oh and I've learned all three of Newtons laws and actually just answered those questions.
  6. Feb 1, 2012 #5
    I also have another question... If you push a box over a rough surface (high friction) at a constant speed, how much net force is there? How do you know?
  7. Feb 1, 2012 #6


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    Staff: Mentor

    As Halls alludes to, there is a concept in physics known as "relative" motion. So the object can move relative to you if it is stationary and you walk past it. I'm guessing that in your intro physics class they just want you to refer to the equation F=ma for this, but I could be wrong. How would you use that equation to try to answer this question?

    There is an equation relating the retarding force of friction to the weight of the object and the coefficient of friction. Can you find the explanation of that equation in your textbook?
  8. Feb 1, 2012 #7
    Um idk I thought that if it had 0 mass then nothing would be moving but you can have 0 acceleration and still have it moving because of a constant velocity.

    Is it Ff = uFn?
    Ff = friction
    u = coefficient of friction
    Fn = normal force
  9. Feb 1, 2012 #8


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    Staff: Mentor

    Don't worry about the 0 mass case. The equation F=ma just says that the mass gives you the ratio between force and acceleration. And yes, if an object is already moving at a constant speed, no force is required to continue that motion (assuming no retarding forces exist like friction or air resistance, etc.)

  10. Feb 1, 2012 #9


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    Gold Member

    Don't worry about massless objects and frames of reference just yet. They are important, but at this point is might just lead to more confusion.
  11. Feb 1, 2012 #10
    Alright thanks for the help! I'm probably going to have more questions later but that's all for now.
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