Question

Newton’s first law of motion states that an object will keep a constant speed and direction unless acted upon by an unbalanced force.

To test this statement, Martin rolled a ball on a long, level street. The ball did not bump into any object, but it eventually came to a stop. How is this possible?

Answer 1

The unbalanced force that caused the ball to stop was friction

Step-by-step explanation:

As Newton's second law states, the acceleration of an object is proportional to the net force applied on the object:

F = ma

therefore, in order to move at constant speed, an object should have a net force of zero (balanced forces) acting on it.

In this case, the ball slows down and eventually comes to a stop: it means that the ball is decelerating, so there are unbalanced forces (net force different from zero) acting on it. The unbalanced force acting on the ball is the friction: friction is a force against the motion of the object, which is due to the contact between the surface of the ball and the surface of the street, and this force is responsible for slowing down the ball

Answer 2

The answer to your question is because of the force of friction between the ball and the ground.

Step-by-step explanation:

Exactly, Newton's first law states that every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impress on it.

After analyzing Martin's experiment we could conclude that Newton's first law of motion is wrong but we must remember that between a body and the surface there is a force of friction that causes that the object comes to stop.

We can not see this force but it is there.