Three boxes (labeled 1, 2, and 3) are stacked on top of each other as shown below. They rest on a floor on Earth. You push on box 2 with a horizontal force of magnitude F. Which of the following is not a third law pair of forces in this system?
The force F that you exert on box 2 and the static frictional force that box 2 exerts on box 1.
The gravitational force exerted by the Earth on box 3 and the gravitational force box 3 exerts on the Earth.
The static frictional force that box 1 exerts on the floor and the static frictional force that the floor exerts on box 1.
The normal force exerted by box 2 on box 3 and the normal force exerted by box 3 on box 2.