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: Mechanics Particular Wheel Problem

  1. Feb 24, 2015 #1
    http://www.uzapping.eu/upload/P3.jpg [Broken]

    2. Relevant equations:
    Only Moment's formulas (I think) or Eventually Euler's Law

    3. The attempt at a solution:
    It's supposed to be an easy problem. But I just don't understand the mechanism and the meaning of the angle on the bottom. So I don't know how to set the problem and how to proceed.
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Feb 24, 2015 #2
    Where is the question? And the image appears to be blank.
  4. Feb 24, 2015 #3


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    The angle at the bottom is the slope of the line through the point of contact with the ground and tangential to the inner circle.
    For rolling wheel questions, it can help to use the fact that the instantaneous centre of rotation is the point of contact of the wheel on the ground.
  5. Feb 24, 2015 #4
    OK, I got the image.
    What are the forces acting when the wheel is in equilibrium?
    which forces provide a torque?
    What will be the direction of friction?
  6. Feb 25, 2015 #5
    Thanks for your replies. For everyone don't see the image, the link is: http://www.uzapping.eu/upload/P3.jpg [Broken]

    However... I know that in order to find the equilibrium condition, the Moment should be equals to zero.
    But what make me confused are manly these things:
    - The particular behaviour of this wheel: I ask myself how this behaviour could change the equations or the calculation. So if someone has enough patience, it would be nice to understand the difference in the procedures between this problem, and the same one but with a normal wheel (which means, the direction of rotation simply follow the tangential force).
    - Why should I choose the bottom point as point of rotation and not the centre of the wheel?
    - Where exactly should be applied this force? On a point on the circle? Make it differences if it's applied in another point? The point is not given.

    Often for me the real problem is to "understand what happens in the problem's situation". Thank you in advance.

    Ps: Sometimes I also don't see the pictures with Firefox, but using Chrome it's ok.
    Last edited by a moderator: May 7, 2017
  7. Feb 25, 2015 #6


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    You would not be choosing it as the point of rotation, it is the point of rotation. You can think of it as rotation about the centre of the wheel plus a linear movement, but if you ask what point is momentarily stationary the answer is the part of the wheel in contact with the ground.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted