Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Angular Momentum

  1. Mar 30, 2006 #1
    I read about angular momentum on wikipedia.com.

    It states that a child sliding down a slide at constant speed would be in mechanical equilibrium but not in static equilbrium. Why? Is it because the child is not stationary? What kinds of forces are involved besides gravity and friction? Do they not cancel each other?

    May seem like a dumb quesiton, but I just need a little push.

  2. jcsd
  3. Mar 30, 2006 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Newton stated that a body would remain at rest or continue at a uniform velocity unless acted upon by an unbalance external force. Does that help?

    (It may be paraphrased but the basics are there)
  4. Mar 30, 2006 #3


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    A body is in equilibirum if the net force is zero [itex] \sum {\vec F} = 0 [/itex]. This means that the acceleration is zero. Such a body is in mechanical equilibrium. But if the acceleration is zero, it can either be that the object moves at constant velocity or that it is at rest (with respect to some frame). If it moves at constant velocity it is in mechanical equilibrium (which had to do with forces) but not in static equilibirum (because it is in motion).

    I am assuming that the slide is straight (no curvature). Otherwise in the curved part, the net force would not be zero.

    The forces are: gravity, friction and the normal force.

  5. Mar 30, 2006 #4
    It makes sense now. Thank you everyone. Have a great weekend! :-)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook