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Homework Help: Speed vs Velocity

  1. Oct 18, 2006 #1
    Is there a difference between the two? The problem reads:

    A grindstone of radius 4.0m is initially spinning with an angular speed of 8 rad/s. The angular speed is then increased to 10 rad/s over the next 4 seconds. Assume that the angular acceleration is constant. What is the average angular spped of the grindstone?

    r= 4m
    Wo= 8 rad/s
    W= 10 rad/s
    to= 0s
    t = 4s

    avg angular velocity = delta theta / delta t
    = 10 - 8 / 4 - 0
    = .5 rad/s

    Is this correct? I only see equations for velocity, not speed.
  2. jcsd
  3. Oct 18, 2006 #2


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    Speed is a scalar (non-directional) quantity, while velocity is a vector. Speed is the magnitude of the velocity of an object.

    This is true of angular speed and angular velocity as well. The angular velocity vector is directed along the axis of rotation of an obect. If you look down the axis of ratation, the direction is toward you for counterclockwise rotation (right hand rule).
    Last edited: Oct 18, 2006
  4. Oct 18, 2006 #3
    in the case of boject moving in a circle theres always an acceleration even though speed is constant bcoz the velocity is always changing
  5. Oct 18, 2006 #4
    Note that acceleration can be a change in the velocity vector.
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