Question

A teacher attaches a ball to a meter long string and whirls it around in a horizontal circle at constant speed. The teacher explains that the string is what makes the ball go in a circle. Why is the string necessary? A) The string is needed to apply a torque to the ball. B) The string is needed to push on the ball to get it up to speed. C) Circle motion requires an inertia which is provided by the string. D) Circle motion requires a force to give it a centripetal acceleratio

Answer 1

The string is needed to apply a torque to the ball.

Answer: Option A

Explanation:

To rotate any object in a circle, the most important factors are force and perpendicular distance around the center. The product of these two factors produces torque, i.e. Forces x vertical distance. An object moving in a circle must exert an internal force to achieve internal acceleration.

In this case, the string is needed for the ball to rotate, because that makes the ball go in a circle. This is done by dragging the object to the center of the circle.