1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Equal to zero if angular velocity is constant

  1. Mar 13, 2010 #1
    1. The problem statement, all variables and given/known data

    Which is equal to zero if angular velocity is constant, normal or tangential acceleration?
    The one with zero angular velocity is a crank. The crank moves at a fixed point.

    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Mar 13, 2010 #2

    rock.freak667

    User Avatar
    Homework Helper

    Re: acceleration

    So which do you think it is and why?
     
  4. Mar 14, 2010 #3
    Re: acceleration

    I think it is the tangential one because that means it is a uniform motion but continuously changing speed? is that correct?
     
  5. Mar 14, 2010 #4

    rock.freak667

    User Avatar
    Homework Helper

    Re: acceleration

    But it is not changing speed, the angular velocity is the same.

    At different points in the circular motion, if you draw a tangent to the circle, you will get the direction of velocity right? Does this tangent always point in the same direction?
     
  6. Mar 14, 2010 #5
    Re: acceleration

    sorry it should be constant velocity. changing direction but constant speed, right?
     
  7. Mar 14, 2010 #6

    rock.freak667

    User Avatar
    Homework Helper

    Re: acceleration

    Yes. So would the tangential velocity be changing is α is defined as α=dω/dt ? Since the direction of the tangential velocity is changing what does that say about acceleration?
     
  8. Mar 14, 2010 #7
    Re: acceleration

    velocity is changing. If that is changing, acceleration is also changing?
     
  9. Mar 14, 2010 #8

    rock.freak667

    User Avatar
    Homework Helper

    Re: acceleration

    Right so if you were to draw the two velocity tangents and then find the change in velocity, it would point towards the center of rotation. So which acceleration is zero?
     
  10. Mar 14, 2010 #9
    Re: acceleration

    Normal acceleration is always towards the fixed point. The normal one?
     
  11. Mar 14, 2010 #10

    rock.freak667

    User Avatar
    Homework Helper

    Re: acceleration

    That would be correct.
     
  12. Mar 14, 2010 #11
    Re: acceleration

    Can you give a summary on how to determine which is zero among the two in different situations?

    How can I determine the tangential acceleration if I have given the angular velocity?
     
  13. Mar 14, 2010 #12

    rock.freak667

    User Avatar
    Homework Helper

    Re: acceleration

    tangential acceleration is related to α by atangential=αr
     
  14. Mar 14, 2010 #13
    Re: acceleration

    so, if normal is zero, then tangential equals the angular acceleration. I only depend on the tangential and normal formula.
     
  15. Mar 14, 2010 #14

    rock.freak667

    User Avatar
    Homework Helper

    Re: acceleration

    no no, the only way for your normal acceleration to be zero is if the object is not spinning. Remember a=ω2r
     
  16. Mar 14, 2010 #15
    Re: acceleration

    so normal is zero in a sliding block?
     
  17. Mar 14, 2010 #16

    rock.freak667

    User Avatar
    Homework Helper

    Re: acceleration

    You mean a sliding block on a curved surface? No, the normal is not zero. In that case there is still a normal acceleration.
     
  18. Mar 14, 2010 #17
    Re: acceleration

    i mean in a mechanism, in a flat surface. the sliding block has zero normal? I'll be back.
     
  19. Mar 14, 2010 #18

    rock.freak667

    User Avatar
    Homework Helper

    Re: acceleration

    Once your object is basically rotating with respect to some point, there will be a normal acceleration.
     
  20. Mar 14, 2010 #19
    Re: acceleration

    I mean in a mechanism, the sliding block, the normal in a flat surface is zero?
     
  21. Mar 14, 2010 #20

    rock.freak667

    User Avatar
    Homework Helper

    Re: acceleration

    ok, what sort of mechanism are you talking about?
     
  22. Mar 14, 2010 #21
    Re: acceleration

    its only a sample, only a schematic drawing.
     
  23. Mar 14, 2010 #22

    rock.freak667

    User Avatar
    Homework Helper

    Re: acceleration

    Can you post a picture of the schematic?
     
  24. Mar 14, 2010 #23
    Re: acceleration

    its only a sketch angular velocity at 2 is constant
     

    Attached Files:

  25. Mar 14, 2010 #24

    rock.freak667

    User Avatar
    Homework Helper

    Re: acceleration

    If your surface is flat in that manner, then there is no normal acceleration.
     
  26. Mar 14, 2010 #25
    Re: acceleration

    what is the normal acceleration doing?
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook