Newton's first law of motion, also known as the law of inertia, states that an object at rest will remain at rest, and an object in motion will continue moving in a straight line with constant velocity, unless acted upon by an external force.

This concept of inertia can be observed in our everyday lives. For instance, when you push a book on a table, it eventually comes to a stop due to the friction between the book and the table's surface. In the absence of this frictional force, the book would continue its motion in a straight line indefinitely.

Another example can be seen in a moving car suddenly coming to a halt. As the car breaks, our bodies tend to lunge forward. This is because our bodies have the inertia of motion, wanting to continue moving forward at the same speed as the car. It is the seatbelt that applies an external force to bring our bodies to rest along with the car.

In summary, Newton's first law emphasizes that objects have a tendency to maintain their current state of motion and it takes an external force to change that state.