Observations: Mass of rubber stopper = W5 0 Be careful with units throug out SPH4U Centripetal Force Lab Name: An object moving along a circular trajectory at constant speed is said to be moving in uniform circular motion (UCM). Any object moving in UCM must be accelerating toward the centre of its circular path, and therefore must also experience a net force directed toward the centre. This net force is called a centripetal force, and Newton's second law for UCM becomes: Fc = mac Where Fc is the net (centripetal) force, m is the mass of the object and a is its inward centripetal acceleration. That acceleration is given by: ac = vz / r Where v is the speed of the object, and r is the radius of the circular path. In this lab, a rubber stopper will be tied to a string and whirled overhead. The centripetal force causing the stopper to move in UCM will be supplied by tension in the string which can be controlled by adjusting the mass (# of washers) hanging on the other end of the string (see diagram). The relationship between the force and the speed of the stopper can then be investigated. Purpose: To investigate the relationship between the inward centripetal force and the speed of an object undergoing uniform circular motion. length of the string/ L tube Materials: radius r Centripetal force kit rubber stopper/ m Stop watch or phone as timer Meter stick Electronic balance Hanging mass/M Procedure: 1. Measure and record the mass of the rubber stopper. 2. Adjust the cord stopper so that the length of string between the rubber stopper and the top of the acrylic tube is one meter. Leave approximately a centimeter between the tube and the cord stopper. 3. Place 6 washers on the string by passing them through the paper clip. 4. Measure the mass of the washers on the end of the string. 5. Carefully swing the rubber stopper overhead in a horizontal circle, regulating the speed so that the one centimeter gap between the tube and the cord stopper is maintained. 6. Once stable circular motion is achieved, measure and record the time required for the rubber stopper to complete ten revolutions. 7. Add two washers to the end of the string and repeat steps 3 - 5. 8. Continue to add washers until you have obtained enough data