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Pulley, Strings, Friction [Please]{Mechanics}

  1. Apr 24, 2011 #1
    Pulley, Strings, Friction [Please..]{Mechanics}[not Solved]

    1. The problem statement, all variables and given/known data

    1) I am really confused about how tension is same on both sides of pulley. Also, how do friction of pulley affect tension in string?

    2) Also want to know how tension provides torque to pulley since tension in each segment is perfectly cancelled out by adjoining string segments.

    3) If possible can anyone give me free body diagram of tension in each segments of various parts in a pulley?

    4) What is the basis of constrained motion? How do i use them to make relations??


    2. Relevant equations

    No equations. Conceptual Problem

    3. The attempt at a solution

    tried a lot. No use.. :(
     
    Last edited: Apr 24, 2011
  2. jcsd
  3. Apr 24, 2011 #2
    NOone here to clear by doubts huh??! !!!!
     
  4. Apr 24, 2011 #3

    Doc Al

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    Tension is the same on both sides of a massless and frictionless pulley.

    I don't understand what you mean 'tension in each segment being canceled out'. For a segment of a massless rope, the net force is zero. But the rope still transmits a force from one end to the other.
     
  5. Apr 24, 2011 #4
    How?!! How does tension change if there is friction and mass on pulley?
     
  6. Apr 24, 2011 #5

    Doc Al

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    Well, something's got to accelerate the massive pulley or overcome the friction. If the tension were the same on both sides, there would be no net torque.
     
  7. Apr 24, 2011 #6
    Okay. Consider this. There is a slit through which the string passes and slit provides friction. is tension same on both sides of pulley? Is tension same on both sides of slit?


    Consider this. there is no block on one side of pulley. Is there tension on string now?
    What is providing centripetal acceleration required by string to move in circular path??


    Consider this: There is two blocks on one side of a pulley, connected in series and one block on other side. is tension same on both sides of pulley and between the two blocks on one side?
    You have cleared a majour part of my doubt . Thanks!
     
  8. Apr 24, 2011 #7

    Doc Al

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    Sorry, but I don't understand what you mean.

    If I understand you correctly, no.
    The string is treated as massless.

    Yes, if the pulley is massless and frictionless.
    No. The rope segment between those two blocks will have a different tension than the other rope segment.
     
  9. Apr 24, 2011 #8
    [​IMG]

    Thanks!

    If tension is different, how do i calculate that?
    May i Know Why? What is the purpose of tension afterall?

    I got you.


    I got you


    How do i calculate that tension??


    Thanks a lot.
     
  10. Apr 24, 2011 #9

    Doc Al

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    A massless rope requires something pulling on each end for it to have tension.

    In the usual manner: Identify the forces acting on each body and apply Newton's 2nd law.
     
  11. Apr 24, 2011 #10
    Thanks but answer the first question also?
     
  12. Apr 24, 2011 #11

    Doc Al

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    About the slit? If it provides friction, then the tension will be different on each side of the slit.
     
  13. Apr 24, 2011 #12
    Can you please explain how?
     
  14. Apr 24, 2011 #13

    Doc Al

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    How much friction does the slit exert?
     
  15. Apr 24, 2011 #14
    10N. Or take it as unknown if you want it that way.
     
  16. Apr 24, 2011 #15

    Doc Al

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    If the force required to overcome friction is 10N, then that's the difference in tension across the slit.
     
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