The Skinny on Velocity
Since velocity is defined as the change in position per second, we can
say the following (for motion along the x- or y-axis):If v is positive, then the displacement is positive: The object is traveling
in a positive direction.If v is negative, then the displacement is negative: The object is traveling
in a negative direction.If v = 0, then the displacement is zero: The object is motionless.(The bar over the v means average.) Because ∆s is a vector, v is also a vector, and
because ∆t is a positive scalar, the direction of v is the same as the direction of ∆s.
The magnitude of the velocity vector is called the object’s speed and is expressed
in units of meters per second (m/s).
Notice the distinction between speed and velocity. In everyday language, they’re
often used interchangeably. However, in physics, speed and velocity are technical
terms with different definitions.
Speed has no direction and is always taken as a positive.Velocity is speed and direction.The magnitude of the average velocity is not called the average speed. Average
speed is the total distance traveled divided by the elapsed time. Average velocity
is the net distance traveled divided by the elapsed time.
Average Velocity vs. Average SpeedAverage speed is not the magnitude of the average velocity unless the
object has moved in a straight line.- Assume that the runner in sample question 3 completes the race