The first law of motion, also known as Newton's first law of motion, is one of the fundamental principles of classical mechanics established by Sir Isaac Newton.

It is often referred to as the "law of inertia." The first law of motion states:

"An object at rest tends to stay at rest, and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced external force."

In simpler terms, this law implies that objects will not change their state of motion unless a force is applied to them.

If there is no net force acting on an object, it will either remain at rest or continue to move with a constant velocity.

This concept of inertia is fundamental to our understanding of how objects behave in the absence of forces, and it forms the basis for much of classical mechanics.