Newton’s Third (3rd) Law of Motion | Law of Action & Reaction

Isaac newton is one of the famous and great scientist and specially known for his work in the field of physics. Sir Isaac Newton has discovered many laws but one of the important Law of the physics which is Laws of motion. There are three laws of motion basically but today we are going to discuss the Newton third law of motion which is applicable in daily life also. These laws describe the relationship between a body and a force acting on that body. So, we will get in touch with detailed information and focus about the third law of motion given by Newton.

What is Newton’s Third Law Definition?

The third law of Newton is considered as the very famous law and is always comes in the normal conversation. This law is very interesting and popular in the field of physics as it the simplest one and easily memorable. When any two objects interact with each other there is a force of push or pull in between them. According to the statement given by Sir Issac Newton : ” For each and every action there is an equal and opposite reaction “ which means that when an external force is applied on one object then there will be an equal and opposite force will be opposed by another object in reverse direction so that it will try to null the net force. In this law, the force will always act as the action-reaction force which is equal but in the opposite direction.

Both of these forces are equal in term of the magnitude but re opposite in direction and these pairs cannot be separated from each other and are coexisting in nature. As this third law is very common so we can see a lot of examples for this law in our daily life when we apply any force on a particular object and in the result of it there will be an equal force is experienced by the first of next due to the second object.

Formula of Newton’s Third Law

F12 = – F21

In this formula F12 is the force which is acting on the first body due to the second body and similarly F21 is telling force which is being acted on the second body due to the first body which is also known as reaction force and opposite to the first one which is denoted by the minus ( – ) sign in front of F21.

Therefore , Force 1 = – Force 2
that is F ( action ) = – F ( reaction )

Let us know something more about both of these forces :

* Both of them Acts simultaneously
* Both are Equal in their magnitude
* Direction is opposite to each other

As , they are equal and opposite forces but these forces do not cancel each other and the reason of it is that these force acts on different bodies, not on the same bodies. So, the above-mentioned points are generally followed by the action-reaction pairs and we also know that the third law is for every action there is an equal and opposite reaction.

Now, as there is action reaction pairs of every object but this does not mean that both two forces will exist together as it can also be possible or not, everything depends on the situation like as an example there is a boy who is pulling a dog but on the other hand the dog is putting his own force not to be pulled in the direction of force applied in this situation the two forces are existing together but on the other hand there is another boy who is trying to pull a toy now in this case the toy is not acting any reaction force on boy so both force are not available here. This clearly indicates that in different situations the presence of forces will be also different.

Examples of Newtons Third Law of Motion

So , now we come to know that the action-reaction law is one of the most important laws of universe which is applicable in day to day life and there are many things which are impossible to do if the third law is not applied like when you swim you place a backward force on water and on the other hand water also exerts a forward force which is in opposite direction and in this way you can swim easily so , this follows the third law of motion which is given by Newton. Now, we have learned a lot about third law but it will get more clear to you when you will learn it with help of examples of daily life just have a look over these examples :

1. Surface force

Whenever we sit on a hard surface our bossy feels pain , this pain occurs because of the third law of motion according to which surface causes equal and opposite force on you upward , this opposite force is dependable upon the weight of body as much heavier the body is more opposite force will be applied in high amount, on the other hand when you sit on the chair or desk for a long you start feeling pain , this also happens because of the Newton’s third law of motion.

2. Friction force of surface

We have faced that it is difficult to walk on a slippery surface, but easy to walk on a rough surface have you wonder it why? This also happens because of the Newton’s third law of motion , when moving on a rough surface there are horizontal components which helps your feet to get more reaction force whereas while moving on a slippery surface there is lack of friction force and we start to take small steps on slippers surface to grab more opposite force , this is the reason why we felt difficult to walk on a slippery surface, but it is easy to walk on a rough surface.

3. Rocket Propulsion

Rocket propulsion is one of the amazing examples of Newton’s third law of motion. If the third law of motion does not exist it is impossible to go in the space. As when the rocket takes off first of it creates a huge amount of force on the surface and in return of which surface reverts and equal force in opposite direction on rocket due to which it exerts out from the gravitational field.

4. Flying of Birds

Birds use there wings to fly, but if third law of motion does not exist then it will be hard for a bird to fly in sky, the birds use action and reaction pair of forces while flying, for flying bird moves their wings downward which pushes the air in downside direction , and due to opposite force this pushes the bird upward which make a bird fly in the sky and this is possible only because of the third law of motion given by Newton.

5. While you fire a piston it moves in backward direction

Have you ever assume that why is a piston moves back when you fire it , this is happening due to the existence of Newton’s 3 law of motion, piston exerts a force on bullet to make it fire which makes gunpowder to burst and bullet moves in the forward direction, but the piston moves in the backward direction this all happens because in this case, the firing of a bullet is an action and the movement of a piston in backward direction is its reaction. A proper way of firing a bullet follow the action-reaction law of Newton.

For every action, there is an equal and opposite reaction

We have discussed and learned almost everything of Newton’s third law of motion like the statement of this law which is – For every action, there is an equal and opposite reaction is a part of Newton’s third law of motion now, here we will be going to discuss space flight.

So, till now we have come to know that for every action there is an opposite reaction let us have an example , when you hit any ball in space then the force which is applied by you on the ball is forward force but in the same context the ball also exerts an equal backward force on our body due to which ball moves in the forward direction but your body do not move in backward just only take a slight change which is not that much noticeable this is due to the friction force which is being applied by the surface on your feet which holds you and make you able to stand on the same position while hitting a ball but what if you reduce this friction force of surface , so just try to reduce this surface friction by having skates so now when you will hit the ball in forwarding direction your body will move in backward direction as there is no friction force exerted by the surface anymore so there will be a movement in your body which can be noticed easily.

So , in the pushing is acting as the action force and the pull will act as the reaction force. This is due to the third law of motion we can see that action-reaction force is applicable here.

Law of Action and Reaction

When any two different object interacts with each other then it is termed as the collision of these objects, this collision is due to the interaction of objects between the forces and these collisions also follows the third law of Newton.

When an object comes from one side and another object comes from the opposite side then both will exert an equal and opposite force with each other and due to which gets stick and collide and due to this collision force the momentum is occupied due to this force. Forgetting this concept to be more clear let us take an example :

In this above image you can see that there are two balls one is of green colour and other of black both of them are moving towards each other When both of the balls collide to each other they will face an equal and opposite force on both of them and with this these balls will get move in opposite directions as the ass of balls is equal so they will get the equal acceleration. There is an action of collision and a reaction which is separating this collision.


So , this was all about the Newton third law of motion we almost explained you each and everything regarding the third law of Newton , this law is considered as the most simpler and universal law which is almost applicable on all objects as there is always some opposite force when we put an action force on any object.

Now , next as in the first and second law of motion you have seen some new things and which are a little bit difficult to remember but the third law of Newton is easy and practical which you have seen in your every day life so it will stick to your memory. You will not be going to face any numerical type problem for this law as there is just a simple formula for third law which F = – F that means when any force acting then there will be another force which is acting on the same object but in opposite direction, you just need to keep this concept in your mind as you can get some of the conceptual problems on this law.

Do not afraid and make physics a fear just take it as practical and you will see how everything will get in to your mind and similar the case is with newtons law just keep the concept and important points clear and you will be able to solve any kind of question-related to this law. So , we hope that you will like it and got the perfect answer to your question although you will not face any problem but still, if occur then you can simply comment below we will answer to your query and solve it for your complete satisfaction. Stay tuned and get physics on your fingertips.

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