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How does weight influence static and knetic friction?

  1. Feb 25, 2009 #1
    we pulled an object using a spring balance {horizontally} what where we measuring with the spring balace? where does mass and weight come in? would my aim be to determine whether weight will have an effect
    on static or kinetic friction? i am just confused with this whole thing! what is the point of this expiremnent?



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Feb 25, 2009 #2

    LowlyPion

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    Welcome to PF.

    The answer is yes.

    The aim is to determine the force needed to move different weights.

    The ratio of the force required divided by the weight is your coefficient of friction. That's what they want you to determine.
     
  4. Feb 25, 2009 #3
    Weight will have an effect on friction as the friction force is the friction coefficient * the normal force. Remember static and kinetic coefficiants are different (kinetic coefficient is lower).

    If you only pulled 1 block, then the aim is to get you to see that the coefficients are different. If you pulled multiple blocks then the aim was to determine the effect of weight.
     
  5. Feb 26, 2009 #4

    tiny-tim

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    Welcome to PF!

    Hi musi! Welcome to PF! :smile:

    Was this mass pulled at a steady speed (when it was moving)?

    If so, then, both when it was stationary and when it was moving, the only horizontal forces on it were the pulling force and the friction force.

    By good ol' Newton's second law, they have to be equal, and by his third law the pulling force has to equal the force on the spring (as shown on the spring's scale)

    Though I don't understand where the difference between mass and weight came into the experiment … unless you could alter the ratio of mass to weight (say, by going to a mountain-top, or by attaching helium balloons to the mass). :confused:
     
  6. Feb 28, 2009 #5
    Oh okay. thank you i get it now.
     
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