Final answer:
Momentum, which is calculated as the product of an object's mass and velocity, describes the quantity of motion possessed by an object.
Step-by-step explanation:
The variable that may be described as "the quantity of motion" possessed by an object is known as momentum. Momentum is a vector quantity, meaning it has both magnitude and direction, and it is calculated as the product of an object's mass and its velocity. The concept of momentum is fundamental in the analysis of collisions and dynamics, as it helps in the understanding of how the mass and velocity of an object contribute to its motion.
Velocity, on its part, is a vector quantity which describes how fast an object moves as well as the direction of its motion, such as 20 kilometers per hour due south. Therefore, momentum (represented by the symbol p) can be comprehensively defined by three factors: the object's speed, the direction of its motion, and its mass.
Momentum is significant in Physics as it helps to predict the resulting motion of objects after they interact. Its conservation is a key principle that applies to isolated systems where no external forces are acting.