What is the 3rd of Newton's laws?

Every action has an equal and opposition reaction: if an object exerts a force on another object, that object will exert an equal and opposite force on the other.

Newton's Third Law is often misunderstood. The statement is: "If one object exerts a force on another object, then that other object exerts an equal and opposite force on the first object." Sometimes this is mixed up with eg WEIGHT and REACTION (R) force. A good example is the Earth-Moon system. The Earth exerts a gravitational pull on the moon (it orbits the Earth!). The moon equally pulls the Earth with exactly the same force (we can see evidence of this in TIDES). At A level we see exactly this effect when Newtons Law of gravitation is explored using F = GM1M2/r^2. The force for the Earth and the Moon are the same!

You can think of Newton's third law as simply saying that forces always come in pairs! If you push on a wall, the wall pushes back on you too. You may have heard of the third law expressed as "for every action, there is an equal and opposite reaction." This means that the forces in the pair have an equal magnitude, but act in opposite directions and onto different objects.

Newton's laws of motion are based on observation from the real life. The third law is based on the observation that whenever one object exerts a force on a second object, the second object exerts and equal force in the opposition direction on the first object.

The exact statement is "For every action, there is an equal and opposite reaction".

For every action force there is an equal and opposite reaction force. Basically all forces come in pairs and must be the same magnitude (size), same type, act in opposite directions and act on different bodies.

Text book definition would be "If object A exerts a force on object B, then object B exerts a force of equal magnitude but in the opposite direction on object A." I find students develop misconceptions. I tend to start with is that the idea all forces come in pairs. We call them Newton pairs. Newton pairs are the same size, opposite in direction, of the same type and act on different bodies.