What is Newton’s first law of motion?
An object at rest stays at rest, and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an external unbalanced force.
Examples of Newton’s first law of motion
Object at rest
A stationary ball kept on the ground experiences zero net force. This is because the downward gravitational force is balanced by the normal force of equal magnitude, acting in the upward direction.
Body at rest stays at rest
Now if there is no external force applied to this stationary ball, it will continue to stay at rest. But if there is an external force applied to this ball, the net force is no longer zero. This causes the ball to accelerate and change its position.
Object in motion
If a ball is moving with a constant velocity on a frictionless surface, it experiences a zero net force. This is because the downward gravitational force is balanced by the normal force of equal magnitude, acting in the upward direction. Also, there is no force of friction.
Body in motion stays in motion
In such a case, the ball will continue to move with a uniform velocity in the same direction. But if we apply an external force to it, the ball will accelerate, decelerate, or change direction depending on the direction of external force.