A box is pushed across a horizontal table at constant speed. Of the forces on it, which pair do we know are equal in magnitude because of Newton's third law? The force of kinetic friction on the box and the force applied to the box by the one pushing it. None of these are interaction pairs. Normal force on the box and the normal force on the table by the box. Normal force on the box and the weight of the box.

Normal force on the box and the normal force on the table by the box.

Explanation:

a) The force of kinetic friction on the box and the force applied to the box by the one pushing it: This pair of forces is compared by Newton's second law.

b) None of these are interaction pairs: If there is a couple of interaction

c) Normal force on the box and the normal force on the table by the box: We know that this pair of forces are equal in magnitude due to Newton's third law, or, the principle of action and reaction, which establishes that when two bodies interact, equal forces and opposite senses appear in each of them.

When a body A exerts a force on another body B, B will react by exerting another force on A of the same modulus and direction although in the opposite direction. The first of the forces is called the action force and the second reaction force:

FAB = - FBA

FAB: It is the force of action of A on B.

FBA: It is the reaction force of B on A

d) Normal force on the box and the weight of the box: This pair of forces is compared by Newton's second law.