Which law states that an object at rest or in uniform motion in a straight line unless acted upon by an external force?

Which law states that an object at rest or in uniform motion in a straight line unless acted upon by an external force?

• A. Newton's Second Law
• B. Newton's First Law
• C. Law of Gravity
• D. Law of Conservation of Energy

Answer: (B)

Inertia is the tendency of objects to resist changes in their motion. An object at rest stays at rest, and an object moving in a straight line at constant speed keeps doing so unless a net external force acts on it. This is Newton's First Law, also known as the law of inertia. It helps explain why a puck on a smooth surface keeps gliding in a straight line until friction or another force slows it down or changes its direction. The other ideas describe different concepts: a force causing acceleration is Newton's Second Law; gravity is the attraction between masses; and conservation of energy is about energy staying the same in a system, not about motion persisting without a net force.

Inertia is the tendency of objects to resist changes in their motion. An object at rest stays at rest, and an object moving in a straight line at constant speed keeps doing so unless a net external force acts on it. This is Newton's First Law, also known as the law of inertia. It helps explain why a puck on a smooth surface keeps gliding in a straight line until friction or another force slows it down or changes its direction. The other ideas describe different concepts: a force causing acceleration is Newton's Second Law; gravity is the attraction between masses; and conservation of energy is about energy staying the same in a system, not about motion persisting without a net force.