Why are graphs used to understand an objects motion?

Hello!

Graphs are used to understand an object's motion because they can show the exact location of the object at any given moment. 

This is done with the help of a reference system. The most common reference system is the Cartesian coordinate system, which describes the location of an object through a set of 2 or 3 coordinates (depending if the system is in 2D or 3D).

Studying graphs of movement, we can know if the movement is cyclical, or the direction of the movement, determine tendencies and overall getting an unambiguous and precise understanding of the motion.

Have a good day!