Question

A ball is whirled on a string, then the string breaks. What causes the ball to move off in a straight line?

Answer 1

Inertia causes the ball to continue to move off in a straight line.

Explanation:

Newton's 1st Law says that an object at rest tends to stay at rest and an object in motion tends to continue to move in a straight line unless acted on by an outside force. The property of mass that causes this behavior is called inertia.

The line that the ball follows after the string breaks will be tangential to the circular path it was previously moving in.

I hope this helps,
Steve