# Law of Inertia

Okay, let’s assume that there is a flat surface and we keep a cricket ball simply on the ground. What will you notice?

The ball is at rest, or we can say it isn’t moving until we apply some force to move it or make the ball come into motion.

Similarly, take an inclined surface on which you slightly roll a ball down. What will you notice about the ball?

The ball will keep moving, or we can say the ball will be in motion until we exert some external force against it to make the ball stop.

So basically, the 1st law of motion says that when a body continues in its state of rest or in uniform motion in a straight line, unless acted upon by a force, Newton’s first law is also known as the “Law of Inertia.”

If we need to calculate different external forces acting on a body, then the net force will be the vector sum of the external forces.

Now let’s talk about the difference between inertia and Newton’s 1st law of motion. Inertia is the resistance of a particular object to any change in its velocity and the changes in the object’s speed or direction of motion.

Whereas Newton’s 1st law states that a physical object that is at rest and an object that is in motion or moving will stay in motion until there is any external force provided on the object, this law refers to inertia.

Newton’s 1st law of motion can be referred to as the law of inertia, and inertia can be referred to as the stillness of an object.