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

Ball Revolving around Stick

  1. Oct 18, 2011 #1
    1. The problem statement, all variables and given/known data

    Two wires are tied to the 150 g ball shown in the figure. The ball revolves in a horizontal circle at a constant speed of 5.0m/s. gravity is 10m/s2.


    Draw a free-body diagram and specify any relevant dimensions or angles.

    Write expressions applying Newton's second law on the ball.

    Calculate the tension in each of the wires.

    If we remove the lower wire, but want the ball to revolve in the same path, what must we do to the ball. (i.e. increase decrease speed). Explain

  2. jcsd
  3. Oct 18, 2011 #2


    User Avatar
    Science Advisor

    Have you read the board rules? You are expected to attempt the problem yourself and SHOW what you have tried to do.
  4. Oct 18, 2011 #3
    Oh, sorry. I'm in a rush and I actually didn't read it. I attempted to make a freebody diagram, but all I came up with was that the two tensions added up equaled to the force of gravity. I don't think that is right though. I feel like there is supposed to be some sort of centripital force involved, but I don't know where
  5. Oct 18, 2011 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    It's not. All three forces, added up using vector addition, equal a. And, it's helpful to separate the forces into x and y components to do the vector addition.

    a is the centripetal force; it does not get included in the freebody diagram. The freebody diagram should only have forces with identifiable, physical causes -- for example, gravity, rope/string tension, forces applied by people or other objects, friction, normal force, etc. The centripetal force is simply the net result of those forces.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook