Gravity
Gravity pulls "down" and the opposite force is provided by whatever is beneath the object.
100km
It pushes the car down which allows the air to pass easier
It is a force which acts in the upward direction.
The reaction force when a boy pushes down on a diving board is the diving board pushing up on the boy with an equal force. This is in accordance with Newton's Third Law of Motion, which states that for every action, there is an equal and opposite reaction.
The force to keep us and nearly everything else on the ground is GRAVITY.
When the skateboarder pushes on the ground with her foot, she exerts a force on the ground in one direction, causing the ground to exert an equal and opposite reaction force on her in the opposite direction. This reaction force propels the skateboard and the skateboarder forward, resulting in acceleration down the sidewalk.
The buoyant force pushes you toward the surface.
The external force acting on the mattress when you are lying down is the force exerted by your body weight. Your body weight pushes down on the mattress, causing it to compress and support you.
Your weight pushing down on the chair is the action force. The reaction force is the force exerted by the chair that pushes up on your body
A bicycle seat exerts a force on a rider by supporting the rider's weight through normal force. When a person sits on the seat, their weight pushes down on the seat, and the seat pushes back up with an equal force (normal force) to support the rider.
Your weight pushing down on the chair is the action force. The reaction force is the force exerted by the chair that pushes up on your body