# Newton's third law confusions [duplicate]

According to Newton's third law of motion, if body A exerts a force on body B, then body B exerts a force on body A that is equal in size but opposite in direction, then how do things move?

• In your picture, only one force acts on each body, so it moves. Aug 16, 2016 at 11:39
• When the wheels of a car gain traction against the road, a reaction force is exerted on the Earth. But because the Earth is much larger that the car, so the car moves but not the Earth, at least not perceptibly (Newton's second law).
– Gert
Aug 16, 2016 at 11:46

In your picture, only one force acts on each body, so it moves or better it has acceleration according to $\vec{a}= \frac{1}{m}\vec{F}$.
It is true that the sum of all forces is zero. This has a consequence only for the whole system made of the two bodies: Since the center of mass of the system always moves in accordance with the second law of dynamics where $\vec{F}$ is the sum of all forces acting on each part of the system, the center of mass has here vanishing acceleration and thus it does move if its initial velocity is zero.