What physical property is embodied in the phrase, "A body in motion tends to stay in motion"?

• A. Force
• B. Inertia
• C. Mass
• D. Momentum

Answer: (B)

The phrase "A body in motion tends to stay in motion" refers to the concept of inertia, which is a fundamental principle in physics articulated by Sir Isaac Newton in his first law of motion. Inertia is the tendency of an object to resist changes to its state of motion. This means that an object will continue to move at a constant velocity in a straight line unless acted upon by an external force.

In this context, the emphasis is on the fact that motion is not inherently lost without interference from outside forces. For example, a ball rolling on a flat surface will continue to roll until friction or another force brings it to a stop. This illustrates inertia in a practical scenario where the continuity of motion is maintained.

In contrast, the other choices involve different concepts. Force refers to a push or pull that can change an object's motion, mass is a measure of the amount of matter in an object, and momentum is the product of an object's mass and its velocity, which involves motion but does not specifically describe the tendency of an object to maintain that motion without external influence. Thus, inertia is the most appropriate term that captures the essence of the phrase.