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Homework Help: Quick friction concept question

  1. Feb 6, 2008 #1
    1. The problem statement, all variables and given/known data

    A box is pulled across a rough horizontal surface with force F. Each time the box moves a distance D, howeveer the angle of F varies. Which angle causes the most/least amount of friction. An angle above/below/horizontal to the surface.

    2. Relevant equations

    3. The attempt at a solution

    I know that the least friction is caused by a force above horizontal and the most is caused by a force below horizontal but I have no clue how to explain it using physics.
  2. jcsd
  3. Feb 7, 2008 #2
    Try imagining the forces resolved into horizontal and vertical components. Does that help?
  4. Feb 7, 2008 #3
    2. Relevant equations,

    Force of Friction = mu*Normal Force

    So if u are pulling bellow the horiziontal, u are pusing the box into the ground, thus increasing the normal force => increasing friction.

    If you pull above horizontal, then u are pulling up the box => less Normal force => less friction

    make sense?

    question ? ask me

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