Displacement and Velocity

• Displacement is the vector difference between the ending and starting positions of an object. It may be very different from the distance the object has travelled along the way.
• Velocity is the rate at which displacement changes with time. It is a vector, too.
• The average velocity over some interval is the total displacement during that interval, divided by the time.
• The instantaneous velocity at some moment in time is the velocity of the object right now!
• Instantaneous velocity is the derivative of position with respect to time.
• Speed is a scalar, which describes the total distance travelled by some object during some time interval. Speed is sometimes equal to the magnitude of a velocity vector, but not always.
• Use some common sense when you have finished a problem: look at the answer and ask yourself, "Is that reasonable?"

Viewgraphs

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