Forces Acting on the Cardboard:

* Gravity (Weight): This force pulls the cardboard downwards due to the Earth's gravitational attraction. Its magnitude is equal to the cardboard's mass multiplied by the acceleration due to gravity (approximately 9.8 m/s²). Its direction is downwards, towards the center of the Earth.

* Normal Force: This force acts perpendicularly upward from the surface the cardboard is resting on. It balances out the force of gravity, preventing the cardboard from falling through the surface. The magnitude of the normal force is equal to the weight of the cardboard, but its direction is upwards, opposite gravity.

Pair Forces:

The normal force and gravity are considered a pair of forces, specifically an action-reaction pair as described by Newton's Third Law of Motion. This law states that for every action, there is an equal and opposite reaction.

* Action: The cardboard exerts a force on the surface (the weight, pulling downwards).

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

Key Points:

* Equal Magnitudes: The magnitudes of the normal force and gravity are always equal when the cardboard is at rest. This ensures the forces are balanced.

* Opposite Directions: The directions of the normal force and gravity are always opposite. One pushes upwards, and the other pulls downwards.

In Summary:

When the cardboard is at rest, the forces acting on it are balanced. The weight (gravity) pulls downwards, and the normal force from the surface pushes upwards. These forces are equal in magnitude and opposite in direction, forming an action-reaction pair.