From left to right, follow the dots in line 1 with your finger. Count a steady beat out loud, and time your motion so your finger crosses a dot at the end of each beat. Don’t pause at the dots, and move as smoothly as you can. A good way to count is to say or think “1 Mississippi, 2 Mississippi,” and so on. Is your finger moving at a constant rate, or is the rate changing?

Show him another sport or something

You need to be more specific.  i really don't know what a "motion map" is.you can draw a graph of an object's position, distance, displacement, speed,velocity, or acceleration versus time, or you can draw a graph of the object's x-position versus its y-position and not give any information about time at all.if the graph presents position or displacement against time,  then constant velocity is a straight line . . i.e. a line that has  constant slope.if the graph shows speed against time, then constant velocityis a horizontal piece of line.if the graph shows acceleration against time, then constant  velocity is a piece of line that lies on the x-axis . . it's value is zero.