Action-Reaction

When you lean against a wall, you exert a force on the wall. The wall simultaneously exerts a equal force on you. Hence you don’t fall over.

The boxer can hit the massive bag with considerable force. But with the same punch he can only exert only a tiny force on the tissue paper in midair.

In the interaction between the hammer and the stake, each exerts the same amount of force on the other.

The force on the orange, provided by the apple, is not cancelled by the reaction force on the apple. The orange still accelerates because the orange and the apple are two separate systems.

In the larger system of orange + apple, action and reaction forces are internal and cancel. If these are the only horizontal forces, with no external force, no acceleration of the system occurs.

An external horizontal force occurs when the floor pushes on the apple (reaction to the apple’s push on the floor). The orange-apple system accelerates.

A acts on B, B accelerates.

Both A and C act on B. They can cancel each other. If they do, B does not accelerate.

Earth is pulled up by the boulder with just as much force as the boulder is pulled down by Earth.

The balloon recoils from the escaping air, and it moves upward.

The rocket recoils from the “molecular cannonballs” it fires, and it moves upwards.

You cannot touch something without being touched.

Geese fly in a V formation because air pushed downward at the tips of their wings swirls upward, creating an updraft that is strongest off to the side of the bird. A trailing bird gets added lift by positioning itself in this updraft, pushes air downward, and creates another updraft for the next bird, and so on. The result of a flock flying in a V formation.