Final answer:
Momentum, defined as the product of a body's mass and velocity, is the term used to describe the quantity of motion with which a body proceeds in a certain direction. It is a key concept in physics that helps explain the behavior of moving objects under various forces.
Step-by-step explanation:
The quantity of motion with which a body proceeds in a certain direction is called momentum. Momentum is a fundamental concept in physics and is dependent on two key factors: the mass of the body and its velocity. Velocity itself is a vector quantity that defines speed in a specific direction, for instance, 20 kilometers per hour due south. Hence, momentum can be concisely defined as the product of an object's mass and its velocity. It is sufficiently important in the study of mechanics that historical physicists like Newton referred to it as the quantity of motion.
Momentum is crucial for understanding various types of motion, such as projectile motion, which considers the movement of an object thrown into the air and is affected only by gravity. In the context of Newton's laws of motion, specifically Newton's second law, momentum plays a pivotal role as it describes how the motion of a body changes when it is subjected to an external force.