Newton’s Third Law of Motion

INTRODUCTION

Sir Isaac Newton was one of the greatest scientists of all time. He was an English Physicist whose contribution to physics and astronomy still had an influential effect on the scientific revolutions. Newton’s laws of motion are mechanics, providing a relationship between the object and motion. It studies the effect of forces acting on an object in motion. He has laid down 3 classical laws of motion used in physics. These 3 laws of motion have revolutionized physics and are still used widely with forecasting capabilities. In this article, we shall be discussing the third law of motion.

THE THREE LAWS OF MOTION

Newton’s First Law of Motion:  A body continues in its state of rest, or uniform motion in a straight line unless acted upon by a force.

Newton’s Second Law of Motion:   A body acted upon by a force moves in such a manner that the time rate of change of momentum equals the force.

Newton’s Third Law of Motion: If two bodies exert forces on each other, these forces are equal in magnitude and opposite in direction.

NEWTON’S THIRD LAW OF MOTION

Newton’s third law of motion provides that all the forces present between two bodies are of an equal magnitude if they are directed opposite. For example, if body 1 exerts a force F₁ on body 2, then body 2 would exert a force F₂ over body 1. Also, these two forces F₁ and F₂ will be of equivalent magnitude however in opposite directions.

Thus,

F₁ = −F₂.

Newton’s third law of motion states that all forces present between two objects are nothing but merely interactions between those two objects in different areas. Therefore, as per the third law, it is just not possible in mechanics that an existing force in an object is not accompanied or associated by an equal and opposite force. This is also known as the action & reaction law.

Further, as per Newton’s third law of motion, at times, the magnitude and direction of the forces are decided and dependent completely on only one object and the other object remains only under influence.

For example, in Object 1, the force exerted by Object 1 over Object 2 can be conveniently called an “action”. Therefore, the force exerted by Object 2 over Object 1 in return, would be called the “reaction”. That is why this phenomenon is called the action & reaction law. As per the above-mentioned example, the force exerted by Object 1, F₁ will be called the “action” and the force exerted by Object 2, F₂ will be called the “reaction”.

However, in the rest of the cases, the magnitude and directions of the forces are decided and dependent on both of the bodies. Also, in those cases, it becomes unrequited to pick out force exerted by one object as the “action” and force exerted by the other one as the “reaction”. In those cases, both the actions and the reactions take place at the same point in time. Therefore, it is of no significance which force has to be given the name of the action and which would be named as a reaction. Both these forces are simultaneous. They are part of a single interaction and run concurrently. No single force would have a subsistence without the other. Therefore, it can be concluded that Newton’s third law of motion is based upon the conservation of momentum.

EXAMPLES OF NEWTON’S THIRD LAW OF MOTION

Birds while flying in the sky, exert forces by pushing the air towards the downward direction, this was the action. In reaction, they experience a force exerted towards the upward direction which aids them in flying. Helicopters, Aeroplanes, and other air transports can take off and fly on this same phenomenon.

If an object is put on a table and a person comes to lift it, the object is already experiencing a force exerted on it in a downward direction due to the effect of gravity. When the person picks the object a force is exerted in the upward direction which makes the person able to pick that object from the table.

When a person walks in the forward direction, a force is exerted in the forward direction. While the ground exerts a force towards the backward direction making the person able to walk continuously. The acceleration of cars, bikes, and other vehicles is also possible due to this phenomenon only. Swimming or rowing of boats by a person is also attributed to the third law of motion.

Similarly, slingshots or pulling of elastic bands, bouncing off a ball, or jumping off a person at a place or on a trampoline, sitting down, and standing up of a person is also attributed to Newton’s third law of motion. Therefore, it is quite evident that this law has a direct application in regular day-to-day life.

CONCLUSION

Newton’s Third Law of Motion is one of the most significant phenomena of mechanics. It is relevant to find out about the forces being exerted on a system or an object. The practical applications of Newton’s Third Law of Motion are very easy to find in daily lives. From the walking or swimming of a person, moving of cars of vehicles, rowing of boats, to flying of birds, contact of bat and ball during a game of cricket or baseball, everything is an example of application of Newton’s Third Law of Motion. Therefore, it can be concluded that Issac Newton has given physics and Aerodynamic forces a better understanding through his Laws of Motion.