# Use Newton's first law of motion to explain why a basketball rolls across the court?

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Newton's first law of motion states that:

In the absence of a net external force, a body is either at rest or moves with a constant velocity.

This has also been stated as a body at rest tends to stay at rest and a body in motion tends to stay in motion.  This law is the reason that when you roll a basketball down the court it will continue rolling along the floor when the ball leaves your hand.  You have imparted a net force of motion to the ball with your hand that gives the ball velocity.  However, we know that eventually the ball will stop rolling.  That is because there is another force at work on the ball: friction.  Friction from contact with the floor and wind resistance are also working against the motion of the ball and will eventually bring it to rest.

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Newton's First Law of Motion states that an object at rest will remain at rest unless acted on by an external force and an object in motion continues remains in motion with the same speed and direction unless acted on by an external force.  This is also called the law of inertia.

A basketball rolling across a court follows this law.  It does not continue with the same speed because there are external forces such as friction between the ball and the floor and air resistance acting to slow the ball down and ultimately bring it to rest.