NEWTON’s LAWS OF MOTION

Newton further studied Galileo’s ideas on force and motion and presented three fundamental laws that govern the motion of objects. These three laws are known as Newton’s laws of motion.

NEWTON’S FIRST LAW OF MOTION:

According to this law - A body continues to be in a state of rest or in a state of uniform motion along a straight line unless compelled by an external force to change its state of rest or of uniform motion. 

This statement of the first law is divided into two parts:

• A body continues to be in a state of rest unless compelled by an external force to change its state of rest. For e.g. a book lying on a table continues to be there unless it is removed by us. The book will not move by itself till we apply force to move it.
• A body continues in its state of uniform motion in a straight line unless compelled by some external force to change this state of the body. In other words, a moving body cannot come to rest by itself. This part of the law is difficult to realise as we find that a ball rolling on the ground does stop after some time. Similarly, when the engine of a moving car is switched off, it stops after travelling some distance. In fact, motion of every body is being opposed by the invisible forces like ‘Air Resistance’ and ‘Friction’ between the body and the ground. If these opposing forces were removed, a body in uniform motion will continue to move uniformly, and never stop on its own.

Newton’s First Law Defines Force

From the above discussion, it is clear that Newton’s first law of motion gives us the definition of force. It says that a force is needed to change the state of rest or of uniform motion of the body. Thus force is defined as an external effort which changes or tends to change the state of rest or of uniform motion of the body in a straight line.