6C Newton's 3rd Law

Newton's Third
Law of Motion

By Jo Johnson

​Equal strength and opposite in direction. Have you ever seen a balloon fly up in the air as the gases inside of it were coming out of the bottom? This is an example of Newton’s Third Law of Motion. The force pushing the balloon up into the air is equal in strength as to the gases coming out of the bottom and opposite in the direction. Forces that act on different objects that are of equal strength that opposite in direction are called action and reaction pairs.

Newton's 3rd law

Open Ended

What is an action and reaction pair?

Newton’s Third Law of Motion.
Action and reaction pairs are everywhere. You cannot push anything unless it pushes back. A dog pulls on his leash and the leash pulls back. The action and reaction are equal and opposite to one another. When you walk, you push backward on the ground with your feet. That is the action. The reaction is the ground pushing forward with equal but opposite force.

Newton’s Third Law of Motion states that for every action, there is an equal and opposite reaction. Another example of this law is a fireman with a firehose. The action is the water spraying out of the hose. The reaction is the fireman being pushed back from the force of the water coming out of the hose.

Open Ended

What does Newton's 3rd Law of Motion tell us?

Action and reaction forces. Action and reaction forces do not cancel each other out. This is because they work on different objects. A swimmer exerts a backward force on the water. The water then exerts an equal but opposite forward action of her hands. So, the action force is acting on the water and the reaction force acts on the hands.

Action & Reaction

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Jet engines work because of Newton’s Third Law of Motion. When the air enters the front of the jet engine, it is squeezed into a combustion chamber. This makes the air really hot. In the combustion chamber, the hot air ignites the jet fuel to form burning gases. The gases expand and create pressure. The pressure forces the gases out of the back of the engine. That is the action. The reaction is the jet engine accelerating forward.

Jet Engines

Multiple Choice

Action and reaction forces acting on an object in opposite directions cancel each other out.

• True

• False