Newtons Law Of Motion




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Newton’s Laws of Motion

Newton’s Laws of Motion are some of the fundamental laws of physics. They have significant scientific applications.

Newton’s laws are a set of physical laws which describe the motion of objects. These laws are found in Newton’s work ‘Philosophiae Naturalis Principia Mathematica’. They have changed mankind’s understanding of the universe. Classical mechanics is based on these laws.

Newton’s 1st Law of Motion

Every object or body continues to be in its state of rest or of motion unless acted upon by an external unbalanced force. This is taken as the definition of inertia. If there is no net force resulting from unbalanced forces acting on an object (if all the external forces cancel each other out), then the object will maintain a constant velocity. If that velocity is zero, then the object will remain at rest. If an additional external force is applied, the velocity will change because of the force.


For instance, on a frictionless surface, a ball would continue to remain at rest until pushed and once in motion, it will continue moving in a straight line until a force causes it to stop or change direction.

Take a tumbler and place a cardboard piece on it. Now put a coin on this cardboard piece and pull out the cardboard with jerk. What happens? If you do it properly, the coin will drop into the tumbler. The reason is ‘inertia of rest’. The force was applied on the cardboard and the coin is left behind because of its inertia of rest.

Newton’s 2nd law of Motion

The rate of change of momentum of a body is equal to the force applied to that body and in the direction of the force. The acceleration of an object is directly proportional to the force applied to that object, in the direction of the force.This law is expressed by the equation, F = ma, where F is the net force acting on an object of mass m with acceleration a. If an object of mass m has an acceleration a (change in velocity with time) then the net force F acting upon that object is the product of its mass and acceleration. It also accelerates as it is moving.


You are pushing a table across a frictionless surface, if you want to speed up the table faster (increase in acceleration), you push harder (increase in force). If the table was replaced with a heavier table (increase in mass), you have to push harder (increase in force) to speed it up at the same rate as before.

Newton’s 3rd law of Motion

Every action has an equal and opposite reaction.
It means that if a force is applied by an object X upon another object Y, then object Y will also exert an equal and opposite force on object X.


When a shooter fires his gun , he experiences the recoil upon the gun. The “kick” felt by the shooter is the reaction force upon the gun which is equal in magnitude to the force that pushes the bullets. How do airplanes fly at high altitudes and space crafts propelled? High altitude airplanes use jet engines; that is, engines burn fuel at high temperatures and expel it backward. In expelling the burnt fuel a force is exerted backward on it which exerts an equal forward force on the airplane. The same principle applies to space crafts.

Newtons laws have a significant use in several engineering applications. Without these laws many modern technologies would not have been possible.

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