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Force required to push an object a certain distance

  1. Nov 11, 2013 #1
    If someone wanted going to push a static object a certain amount of distance how would you calculate the force the person needs to apply to the object?
    I know you have to take the static force of friction into account so lets say the force of static friction is 10N to get the object moving, I know you would have to take the Fnet to find the total force the object is given, Fa-10N. And then lets say the object has kinetic force of friction of 5N, how would you determine the force the man needs to push the object with to move the object 2 meters? And lets say the object ways 5kg. I just have no clue how I would be able to find the force. Does anybody have any equations that might help me or can explain this to me? I feel like im missing something.
     
  2. jcsd
  3. Nov 11, 2013 #2

    Nugatory

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    Staff: Mentor

    Once the object starts moving, it will continue moving at a constant speed (that is, zero acceleration) if the net force on it is zero - and that happens when you apply 5N to overcome the opposing dynamic friction.

    So in your example:
    - An initial force of slightly over 10N is required to overcome the static friction and start the object moving.
    - Once it's moving, 5N will keep it moving.
     
  4. Nov 12, 2013 #3

    Borek

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    Looks like you are under false impression that the force will depend on the distance - it won't.
     
  5. Nov 12, 2013 #4

    adjacent

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    As I suggested in your previous thread,If you make it move with a force F,it will continue to move until the force is removed.Once you remove the force,Friction will decelerate it(F=ma)and make it stop.You can find the distance traveled using kinemetics equations,once you know the deceleration and its initial speed(at the time the force was removed)
     
  6. Nov 13, 2013 #5

    CWatters

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    johnnnnyyy - Are you talking about giving a box a short shove to get it moving? In which case it will reach some initial speed and you will have given it some Kinetic Energy. It will then slow down and stop as kinetic friction converts that to heat.

    You can work out how much KE you need to give it to make it slide 2m....If the kinetic force of friction of 5N then you need to give it 5 x 2 = 10 Joules of KE but the whole answer isn't quite that simple..

    If the static friction is 10N then you need to apply at least that much force to get it moving. If you continue to apply that much force the box will accelerate because the kinetic friction is lower. Provided you push with more than 5N, at some point it will have acquired enough KE to slide the remaining distance on it's own and you can stop pushing. The remaining distance will be less than 2m so 10 Joules is no longer the energy needed to give it.

    In short there is no one answer for the force required. You could reduce the force from 10 down to 5N once it's moving and push it the whole way with 5N... or give it a very short push with a much higher force, say 1000N (which it give it 10 Joules in quite a short distance compared to 2m) and let it slide the rest of the way.
     
    Last edited: Nov 13, 2013
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