Average velocity and average speed


When a particle has moved from position xi to position xf during the time interval Dt = tf - ti, its average velocity vavg is 



vavg    is a vector; it has a direction and a magnitude.

The average speed Savg is 


Savg does not have a direction.  It only has a magnitude and it is always positive. Savg is an example of a scalar quantity. 

x versus t graph




Average velocity is the slope of the straight line connecting the initial and final points on the x(t) curve.


A particle moving on a straight line takes Dt1 = 100 sec to move from x1 = 5.0 m to x2 = 20. m and it takes Dt2 = 150 sec to move back to position x3=- 5.0 m.  What is the particle average velocity and average speed during its total journey?