1. Not finding help here? Sign up for a free 30min 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!

Rolling and climbing cylinder

  1. May 5, 2015 #1
    1. The problem statement, all variables and given/known data
    The question says:
    A uniform solid cylinder rolling with angular velocity ##\omega## along a plane surface strikes a vertical rigid wall. With what angular velocity the cylinder begins to roll up the wall because of impulsive blow? It is observed it rolls without sliding after striking the wall.
    1. ##\omega##/2
    2. ##\omega##/3
    3. ##\omega##/5
    4. ##\omega##/4

    2. Relevant equations
    ##I_1\omega _1=I_2\omega _2##

    3. The attempt at a solution
    Can we conserve angular momentum along the point at which the cylinder strikes the wall? I don't think so because that point gives an impulse to the cylinder.
     
  2. jcsd
  3. May 5, 2015 #2

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    what moment would that impulse have about that point?
     
  4. May 5, 2015 #3
    Since it passes through it, zero?
     
  5. May 5, 2015 #4

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Yes.
     
  6. May 5, 2015 #5

    ehild

    User Avatar
    Homework Helper
    Gold Member

    Friction plays the main role. During the collision, some impulsive force of friction is exerted on the cylinder. That force causes upward acceleration and its torque changes the initial angular velocity. Both the momentum and the angular momentum change.
     
  7. May 5, 2015 #6

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Indeed, but that also has no moment about the point of contact, so the OP's proposed method works fine.
     
  8. May 5, 2015 #7

    ehild

    User Avatar
    Homework Helper
    Gold Member

    The cylinder slides during the contact, it does not roll.
     
  9. May 5, 2015 #8

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Not according to the OP.
     
  10. May 6, 2015 #9
    Okay then, I am a little confused about the conditions for applying conservation of angular momentum. Is it that the torque around it should be zero?
     
  11. May 6, 2015 #10

    ehild

    User Avatar
    Homework Helper
    Gold Member

    When the rolling cylinder hits the wall, it rubs the wall. There is sliding friction. The collision takes some time when the impulsive force and impulsive torque take effect. As a result, the cylinder looses its horizontal velocity and gains an upward velocity, and also its angular velocity changes.
     
  12. May 6, 2015 #11

    ehild

    User Avatar
    Homework Helper
    Gold Member

    You can apply the the torque equation with respect of a fixed axis or with respect to the CM. Some Δt time is needed to stop the horizontal motion of the cylinder. During that time, the surface of the cylinder slides on the wall. There is no instantaneously fixed axis of rotation.
     
  13. May 6, 2015 #12

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    I see no reason to assume that. If the normal impulse is J, the frictional impulse due to static friction is up to ##\mu_sJ##. If that is enough to provide the vertical velocity consistent with the angular momentum conservation then no slipping.
    If we do allow slipping on contact, is there enough information to solve the problem? I doubt it.
     
  14. May 6, 2015 #13

    ehild

    User Avatar
    Homework Helper
    Gold Member

    Have you solved the problem? Have you got one of the given values?
     
  15. May 6, 2015 #14

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Yes.
     
  16. May 6, 2015 #15

    ehild

    User Avatar
    Homework Helper
    Gold Member

    Well, you are right, angular momentum is conserved with respect to the contact point at the wall. The result is the same obtained with my method.
     
  17. May 6, 2015 #16
    Ok now it's clear to me. Thanks haruspex and ehild. :).
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Rolling and climbing cylinder
  1. Rolling Cylinder (Replies: 6)

  2. Rolling Cylinders (Replies: 8)

Loading...