Law of inertia

Definition

The law of inertia states that an object at rest will remain at rest, and an object in motion will continue in motion with a constant velocity, unless acted upon by a net external force. It is also known as Newton's First Law of Motion.

5 Must Know Facts For Your Next Test

1. The law of inertia describes the natural tendency of objects to resist changes in their state of motion.
2. Inertia is directly related to the mass of an object; greater mass means greater inertia.
3. A net external force is required to change the velocity (speed or direction) of an object.
4. Newton's First Law applies to both linear and rotational motion.
5. The concept of equilibrium involves zero net force, meaning an object either remains at rest or moves with constant velocity.

Review Questions

• What happens to an object at rest according to the law of inertia if no external force acts on it?
• How does mass affect the inertia of an object?
• Explain how Newton’s First Law applies when driving a car and suddenly applying brakes.

Related terms

Net Force: The overall force acting on an object when all the individual forces are combined.

Equilibrium: A state where the sum of forces and torques acting on a system is zero, resulting in no acceleration.

Newton's Second Law: $F = ma$, which states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.