Final answer:
Momentum, represented by the symbol p, is the variable that describes an object's quantity of motion and includes both mass and velocity, with direction considered for the velocity vector.
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 an important concept in Physics and is represented by the symbol p. It is calculated as the product of an object's mass (m) and its velocity (v). Momentum not only includes the mass and velocity of an object, as kinetic energy does, but also includes the direction of the moving object's velocity vector, making it a vector quantity. Because momentum involves both mass and the velocity vector, changes in either quantity will affect an object's momentum.
To understand momentum better, consider that it essentially measures how difficult it would be to stop a moving object. A larger momentum means that more force would be required to bring the object to rest. For example, a heavy truck moving at a high velocity has more momentum than a small car moving at the same speed because the truck has more mass.