Circular Motion

Description

A heavy ball is attached to a string and swung in a circular path in a horizontal plane as shown in the animation. At the point indicated the string suddenly breaks at the ball. Four animations represent possible results when the string breaks at point P.

Question

Which of the four animations properly represents the path of the ball if the string breaks at point P?

Instructor Resources

Reference: See Giancoli-PA: 5-1, Giancoli-SE: 3-8.

Answer: Animation B, the ball moves tangent to the circle at point P (not shown). This problem is an excellent warm up for the discussion of uniform circular motion. Students often have a hard time with the cause of uniform circular motion. Here, the string is the cause of the ball's acceleration towards the center of the circle. In fact, without it, there is no longer an acceleration and the ball continues at a constant velocity which is tangent to the circle at point P. Students will often laugh at animations such as Animation D, even though they will answer this question incorrectly (choosing this answer) on the FCI.

Script Author: Melissa Dancy