Name: ____________________________ LAB: CENTRIPETAL FORCE PHYSICS - TALBOO Date: ______________ Period: ________ OBJECTIVE Students will investigate the relationship between centripetal force, velocity and radius for a revolving rubber stopper. MATERIALS - Stopwatch Metal tube Calibrated mass set Calculator - Nylon string - Rubber stopper with hole - Paper clip PROCEDURE 1. Thread the free end of the string through the metal tube. The length of string between the rubber stopper and the handle should be 0.5 meter (marked in red line on your string). 2. Hold the free end of the string firmly in one hand and the metal tube in the other. Make sure you have an area clear of other students. Begin to swing the stopper slowly in a horizontal circle overhead. a. Feel the pull on the string as the speed of the stopper increases. As the speed of the stopper increases, does the pull on the string increase or decrease? b. Try swinging the rubber stopper at a constant speed and slowly let some string out to increase the radius of the circle. How does the force on the string change? 3. Return the string to its original half-meter length. Tie a loop in the free end of the string and hook the paperclip to it. 4. Hook a mass on the end of the paper clip. Convert this mass into weight and record this value in the data table. 5. Slowly begin to swing the rubber stopper overhead. Increase or decrease the speed of rotation until the red line is lined up with the top of the metal tube. 6. The centripetal force and the hanging weight are equal when the red line is stationary at the top of the metal tube. 7. Find the period (T) of the rubber stopper by timing 20 revolutions and then dividing by 20. Record this value in the data table. 8. Find the rubber stopper’s velocity (v) by v = 2πr / T where r = 0.5 m. Record this value in the data table. 9. Calculate v2 and record this value in the data table. 10. Add an additional 50 g to the paper clip and repeat steps 5 – 9. DATA Mass (g) Weight = Centripetal Force (N) 0 0 50 100 150 200 250 300 350 T (s) v (m/s) v2 (m2/s2) 0 0 ANALYSIS 1. Make a graph of centripetal force vs. velocity and a graph of centripetal force vs. v2. 2. The graph that better approximates a straight line represents the relationship between force and velocity. Which graph better approximates a straight line? Draw a best fit line on that graph. 3. According to your graphs, is force dependent of velocity or velocity squared? 4. What will happen to the centripetal force acting on an object if its velocity is doubled? 5. If your radius doubled, what would need to happen to your centripetal force? (assume constant velocity and mass) 6. If your radius increased, what would need to happen to your velocity? (assume constant centripetal force and mass)
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