Newton's Third Law and Pair Forces

Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. This means that whenever one object exerts a force on another object, the second object exerts an equal and opposite force back on the first. These are called pair forces.

Forces on the Cardboard Box

When the cardboard box is at rest, the following forces are acting on it:

* Weight (Force of Gravity): This is the force pulling the box downwards due to Earth's gravity. Its direction is straight down, and its magnitude is equal to the box's mass times the acceleration due to gravity (9.8 m/s²).

* Normal Force: This is the force exerted by the surface the box is resting on, pushing upwards on the box. Its direction is straight upwards, and its magnitude is equal to the weight of the box. This force balances the weight of the box, keeping it at rest.

Comparing the Forces

* Magnitude: The magnitude of the weight and the normal force are equal. This is essential for the box to be at rest.

* Direction: The weight and the normal force are opposite in direction. One is pulling down, and the other is pushing up.

Summary

When the cardboard box is at rest, the pair forces of weight and normal force are equal in magnitude and opposite in direction. This ensures the box remains in equilibrium and doesn't move.