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The Concept of Work

  1. May 30, 2014 #1
    1. Hey everyone! I am currently studying for my final exam and I am trying to review work to start out. When I was reading, it gave me an example of where a person is holding a text book and the person moves the textbook in the horizontal direction. Under the picture they gave an explanation which says: No work is done on a textbook when carried in the horizontal direction at a constant velocity.



    2. None



    3. Considering Work depends on displacement, I just thought that if you move a textbook up or down and that is displacement, then why can't there be displacement if you move the textbook (or anything) horizontally?
     
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  3. May 30, 2014 #2

    Fredrik

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    Do you know the definition of "work"? I mean, do you know how to calculate it? What do you get if you use that formula to calculate the work performed moving a book horizontally?
     
  4. May 30, 2014 #3
    From the site that I am reading from....Work is the "force-displacement product". The formula shows to be: W = FΔs cos θ
     
  5. May 30, 2014 #4
    Ok...so is it because since there is a vertical force and the displacement is horizontal, then that's why work is not being done? So with that in mind, if there was a horizontal force and a horizontal displacement, then there would be work being done on the textbook?
     
  6. May 30, 2014 #5

    Fredrik

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    Right. The ##\theta## in that formula is the angle between the force vector and the displacement vector. So when the force and the displacement are perpendicular, we have ##\cos\theta=\cos\frac\pi 2=0##. When they are parallel, we have ##\cos\theta=\cos 0=1##.
     
  7. May 31, 2014 #6
    Thank you so much!!
     
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