Forces Acting on the Cardboard

* Weight (Force of Gravity): This acts downwards, towards the center of the Earth. Its magnitude is determined by the cardboard's mass and the acceleration due to gravity (approximately 9.8 m/s²).

* Normal Force: This is the upward force exerted by the surface the cardboard is resting on. It acts perpendicular to the surface. In equilibrium, the normal force perfectly balances the weight, ensuring the cardboard stays stationary.

The Key Concept: Newton's Third Law

Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. This means:

* Action: The cardboard exerts a force (its weight) on the surface it's resting on.

* Reaction: The surface exerts an equal and opposite force (the normal force) back on the cardboard.

Comparison of Forces

* Magnitude: The normal force and the weight have the same magnitude. This is necessary for the cardboard to remain at rest.

* Direction: The normal force acts upwards, directly opposite the weight's downward direction.

In Summary

When the cardboard is at rest, the forces acting on it are balanced. The weight (downward force) and the normal force (upward force) are equal in magnitude and opposite in direction. These forces are a perfect example of Newton's Third Law in action.