Which principle emphasizes that an object will remain at rest unless acted upon by an external force?

• A. Principle of Acceleration
• B. Principle of Inertia
• C. Principle of Action and Reaction
• D. Principle of Momentum

Answer: (B)

The principle that emphasizes an object will remain at rest unless acted upon by an external force is known as the Principle of Inertia. This concept stems from Sir Isaac Newton's First Law of Motion, which states that an object at rest will stay at rest, and an object in motion will continue in motion with the same speed and direction unless acted upon by a net external force.

This principle is fundamental to understanding motion and provides the basis for explaining how forces affect the state of an object. For example, a stationary ball will not roll until a force, such as a kick or push, is applied to it. Inertia is directly related to mass; more massive objects require greater forces to change their state of motion.

In contrast, other principles such as acceleration, action and reaction, and momentum, each address different aspects of physics, emphasizing the relationships between forces, movements, or quantities of motion rather than the inherent tendency of objects to maintain their state unless influenced by external forces.