Newton’s third law

Definition

Newton's third law states that for every action, there is an equal and opposite reaction. This means that forces always come in pairs, acting on two different objects.

5 Must Know Facts For Your Next Test

1. The law implies that forces between two interacting objects are equal in magnitude and opposite in direction.
2. It applies to both contact and non-contact forces, such as gravitational and electromagnetic forces.
3. The third law is fundamental to understanding the conservation of momentum in isolated systems.
4. In a collision, the force one object exerts on another is matched by a force exerted back on the first object.
5. Rocket propulsion works due to Newton's third law; the expulsion of gas creates an equal and opposite thrust.

Review Questions

• What does Newton's third law state about forces?
• How does Newton's third law apply to rocket propulsion?
• Can you give an example where Newton’s third law is observed in everyday life?

Related terms

Newton's First Law:

An object will remain at rest or move in a straight line at constant speed unless acted upon by a net external force.

Newton's Second Law:

$F = ma$, where $F$ is the net force applied to an object, $m$ is its mass, and $a$ is its acceleration.

Momentum:

$p = mv$, where $p$ represents momentum, $m$ represents mass, and $v$ represents velocity. It describes the quantity of motion an object has.