Newton’s First Law of Motion

Newton’s first law of motion states that every body continues in its state of rest or of uniform motion in a straight line, unless it is compelled by some external force to change that state.

Explanation of Newton’s First Law of Motion:

Newton’s first law consists of three parts:

(i) Without applying an external force, a body at rest continues to be at rest. This part is self-evident. For example, we find in day-to-day life that every object continues to lie where it is unless we move it.

(ii) Without applying an external force, a body in uniform motion continues to move uniformly. This part is slightly difficult to realize because in everyday life, 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 traveling some distance. In fact, motion of bodies is being opposed by the invisible forces like air resistance and the force of friction between the body and the ground. If these forces were removed, a body moving uniformly shall never stop on its own.

(iii) Without the application of an external force, a body cannot change its direction of motion, i.e., it continues to move along the same straight line. For example, to turn a car moving over a straight road, we have to apply force on the steering wheel of the car. Similarly, a bike cannot change its straight path on its own. We have to turn its handle.

Newton’s First Law Defines Force

According to Newton’s first law of motion, a body continues to be in a state of rest or of uniform motion along a straight line, unless it is acted upon by an external force to change its state. This means force applied on a body alone, can change its state of rest or state of uniform motion along a straight line.

Hence, we define force as an external effort in the form of a push or pull that moves or tries to move a body at rest; stops or tries to stop a body in motion; changes or tries to change the direction of motion of a body.

Hence, Newton’s first law defines force.