Newton’s First Law or Law of Inertia
Newton’s First Law or Law of Inertia :- If an object is at rest, then it will remain at rest and if it is in motion, then it will remain in motion in the same direction unless an external force is applied on it. This law is also called “Newton’s first law of motion” or “law of inertia”.
Let us first talk about Inertia, what is Inertia?
Inertia is the inability of an object to change its state on its own.
An object can neither automatically come to motion from rest, nor from rest to motion, nor can an object automatically change its direction of motion. This inability of the object is inertia. Inertia means “to resist the change of state”.
Measurement of Inertia : –
The greater the inertia of an object, the greater the mass of that object. For example, if a person wants to push a truck and bring it in motion, this task will not be easy, because the mass of the truck will cause it to resist too much to change in its state, that is, due to the mass Inertia will also be higher.
Therefore, “inertia is proportional to the mass of the object”.
Examples of Inertia:-
(a) When a bus suddenly starts / stops, passengers fall backwards / forwards.
(b) A carpet is beaten with a stick to remove its dust.
(c) Athlete runs some distance before making a jump.
(d) A coin kept on a cardboard on a glass tumbler, on striking hard the cardboard, the coin falls into the glass tumbler.
The first law can be summarized in the following figure:-
Why is Newton’s first law of motion also called the law of inertia?
The word inertia means “lack of activity or interest”, or “unwillingness to make an effort” or “Inactive”. Newton’s first law also talk about inability of an object to change it’s state of rest/motion without any external effort. So this is the reason that Newton’s first law is also called The Law of Inertia.