Which statement best describes the law commonly referred to as the Law of Inertia?

Which statement best describes the law commonly referred to as the Law of Inertia?

• A. Every object persists in its state of rest, or of motion in a straight line, unless acted upon by an outside force
• B. Force equals mass times acceleration
• C. For every action, there is an equal and opposite reaction
• D. Energy is conserved in all interactions

Answer: (A)

Inertia is the tendency of matter to resist changes in its motion. That means an object will stay at rest or keep moving in a straight line at constant speed unless a net external force acts on it. The statement that describes this exactly says an object remains at rest or continues moving straight unless something external changes its motion. That captures inertia because it focuses on the resistance to change in motion, not on how forces produce acceleration or on energy or action–reaction principles. The other ideas describe different principles: force equals mass times acceleration is Newton’s second law and explains how forces change motion; the equal-and-opposite reaction is Newton’s third law about interactions between bodies; and energy conservation is a separate principle about how energy can be transformed but not created or destroyed.

Inertia is the tendency of matter to resist changes in its motion. That means an object will stay at rest or keep moving in a straight line at constant speed unless a net external force acts on it. The statement that describes this exactly says an object remains at rest or continues moving straight unless something external changes its motion. That captures inertia because it focuses on the resistance to change in motion, not on how forces produce acceleration or on energy or action–reaction principles.

The other ideas describe different principles: force equals mass times acceleration is Newton’s second law and explains how forces change motion; the equal-and-opposite reaction is Newton’s third law about interactions between bodies; and energy conservation is a separate principle about how energy can be transformed but not created or destroyed.