Bill Jameson (DeForest Area HS, DeForest, WI) sent us a clever, inexpensive lab idea for studying centripetal force. This is an improvement on an idea he had written for The Physics Teacher in December 1999. The photo shows the setup. A Dual-Range Force Sensor is mounted on the rotating board. A Light Sensor is fastened near it, pointing down. On the other end of the board, the LabPro is taped to counterweight the system. A mass has been attached to the force sensor. When the system is spun, the Light Sensor passes over a flashlight, which allows the students to determine the time for one rotation. In one run, you can measure the centripetal force for several different angular speeds as the device slows down in its rotation. One graph gives you the force data for many different rotation speeds. The period can be determined from the time between peaks from the Light Sensor, and the force is measured directly.