If an object has a mass of 20 kg, what is the force of gravity acting on it on earth?

That force is what most people would call the object's "weight".

Wherever the object is, its weight is

                            (mass) x (acceleration due to local gravity) .

On Earth, the acceleration due to gravity is   9.8 m/s² . (rounded)

The object's weight is      (20 kg) x (9.8 m/s²)  =  196 newtons .

                                                                   (about 44.1 pounds)

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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.