A child picks up a tennis ball tied to the end of a rope. He swings the rope around, over his head, in a circle. Once the ball is spinning, he lets go of the string and the ball goes flying. Explain which of the following images correctly shows which way the ball will fly and why.

The ball will fly tangential to the original circle

Explanation:

The image here is missing, however we can still answer to the question.

In fact, the circular motion of the ball when it is tied to the rope is a combination of two separate effects:

1- The centripetal force, in the form of the tension in the rop, that pulls the ball at any time towards the centre of the circular path

2- The inertia of the ball, which tends to continue its motion in a straight direction, tangential to the circle and perpendicular to the direction of the centripetal force

When child let the string go, there is no more tension in the string acting on the ball, and therefore, there is no longer a centripetal force.

As a result, number 1) disappears, and therefore there is only the inertia of the ball that will determine its motion: and therefore, the ball will continue its motion straight in a direction tangential to the original circle.

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