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Calculating Force

  1. Jan 18, 2013 #1
    Hi,

    Consider a block sits on a table and its weight is 25N.So its weight is acting downwards
    and I want to move this block horizontally and I am applying a force of 30N.

    How I can calculate whether with this Force body moves?

    Cheers

    Abraham
     
  2. jcsd
  3. Jan 18, 2013 #2

    Low-Q

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    Gold Member

    If you use 30N of force to move the block at constant velocity, there is friction between the table and the block that is the cause of neccessary force. If you must apply 30N to make it move in the first place, some of that force is used to accelerate the block. Hard to say what the acceleration is untill the block moves at constant velocity. Also hard to calculate this as both acceleration and friction are unknown.

    Vidar
     
  4. Jan 18, 2013 #3
    Hi,
    If I take coificient of friction as 0.4 for wood table.
    But I am not getting acceleration figure.I just want to move it from rest
    and use a force by pushing it with hand.
     
  5. Jan 18, 2013 #4

    Doc Al

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    Staff: Mentor

    Use the coefficient of friction to calculate the maximum value of static friction. That will tell you if your 30 N force is sufficient to get it moving.
     
  6. Jan 18, 2013 #5
    So friction helps in movement,right?If my block would have been in free space compared to resting on a table with 0.4cof-->pulling force reuired is 0.4 times less than that in free space.
     
  7. Jan 18, 2013 #6

    SteamKing

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    Friction acts to retard movement. If friction acted otherwise, nothing could ever stay still.
     
  8. Jan 18, 2013 #7
    right.Friction in free space is ZERO,I was thinking it is 1.
     
  9. Jan 18, 2013 #8

    SteamKing

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    Instead of friction, perhaps you were thinking of sliction.
     
  10. Jan 19, 2013 #9

    BruceW

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    lol. As Doc Al was saying, you can calculate the max friction force, using the coefficient of friction and the normal force (weight, in this case). This max friction force is the minimum pulling force to cause movement of the block, because the friction force will take whatever value is necessary to stop movement. (until its max value is reached, in which case it will still oppose movement, but will not be enough to stop movement from happening). In free space, there is no friction, so the minimum pulling force is zero (as you would expect).
     
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