The laws of Newton are three principles that describe the motion of bodies, for which are based on a referral system with real strength and speed constant. Next, we will study Newton’s Third Law .

What is Newton’s third law?

It is about the principle of action and reaction . The postulate of this law says that every action generates an equal reaction , but in the opposite direction.

The formula of Newton ‘s third law is expressed as follows:

F _1-2 = F _2-1

The expression defines that the force of body 1 on body 2 (F1-2), that is, the action force, is equal to the force of body 2 on body 1 (F2-1), or reaction force. The bottom line is that the reaction force will have the same direction and magnitude as the action force, but in the opposite direction to it.

Characteristics

The forces always appear in pairs of equal magnitude, with opposite direction and are located on the same line.

On the other hand, it is important to know that the action and reaction forces do not cancel each other out , although they have similar value and opposite directions, since they act on different bodies.

Newton’s third law example

These are some simple examples of how Newton’s third law works.

• When we try to move a sofa, or any heavy object with respect to our body. The action force that we apply to the sofa causes it to move towards the direction where we exert that force, but at the same time, this object generates a reaction force in the opposite direction that we perceive as a resistance of the object.
• If we want to jump up, it is as if we were pushing the ground to be able to propel ourselves. The reaction of the ground is what makes us jump up.
• When we push a person or any object, we make a movement in the opposite direction. This is a consequence of the reaction that the other person or object has on us, although, really, it does not try to push us (if it is an inert body).
• An elevator is raised from almost street level to a certain floor. It feels two forces: one downwards, which refers to its own weight and the people inside it, and another upwards, which is the pull of the cable that supports it. There the forces of action and reaction are evident.
• The fire hose has a handle that firefighters must hold very firmly because the force of the water will immediately move the hose in the opposite direction.