7.5 Newton’s Third Law of Motion
The Law of Action and Reaction
For every action, there is an equal and opposite reaction that exists both in magnitude and direction against the object from which the force originated.
To best explain this law, we must define what specific type of force is known as a ‘Normal’ force.
[latex]\begin{align*} (F_N) \end{align*}[/latex]
This type of force acts upward and is opposite to the force of gravity. Take yourself for example. You are probably sitting in a chair somewhere, reading this resource. In this case, the forces acting upon your body are:
- The force of gravity
- The ‘normal’ force
Gravity is pulling everything down, correct? Well, why doesn’t it pull you right through your chair onto the floor? Or better yet, why doesn’t it pull you straight through the floor or the ground beneath you? It sounds absurd, I know, but it’s because a normal force is acting against gravity in an equal but opposite way. The force your body is exerting downward on the chair is equally counteracted by the normal force of that chair on you.
