8.2.1 Newton’s first law of motion

Therefore, we conclude that everybody continues in its state of rest or of uniform motion in a straight line unless and until it is compelled by some unbalanced force to change that state. This is the statement of Newton’s First Law of Motion.
So, Newton’s first law of motion may be used to define force. It also defines another concept called inertia. The property of a body by virtue of which it is unable to change its state of rest or of uniform motion in a straight line is called inertia.
You can do another activity to understand the concept of inertia.