Newton's Third Law
The law stating that whenever two objects interact, they exert forces on each other that are equal in magnitude and opposite in direction.
Governing formula
F_A_to_B = -F_B_to_A
SI unit
N
In depth
Action-reaction pairs act on different bodies, which is why they do not cancel out for a single body's free-body diagram. This law ensures conservation of linear momentum.
Examples in the real world
A rocket expelling hot gas downward generates an equal and opposite upward thrust force propelling the rocket into space.