Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025
Definition
Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. This means that forces always come in pairs, acting on two interacting objects.
5 Must Know Facts For Your Next Test
The law implies that forces are mutual and occur simultaneously.
An example includes a swimmer pushing against water; the water pushes back with an equal force.
Action-reaction forces act on different objects, not on the same object.
The magnitude of both forces is always equal, but they are in opposite directions.
This law is fundamental in understanding the conservation of momentum.