How did the period of revolution change to account for a largerand smaller radius?

Physics 310 Lab 13 – Uniform Circular Motion

Tutorial includes complete laboratory (including methods andmaterials, experimental data, full explanations, and diagrams) withthe following questions answered:

Lab Exercise

Experiment 1: Balancing the Centripetal Force

Table 1: Period data for revolving washer with variable radius

1. If you suddenly cut the string connected to your rotating mass,what would be the direction of its velocity? Draw a diagram showingthe direction of motion of an object just cut from a circularrevolution.

2. How did the period of revolution change to account for a largerand smaller radius? How did the angular frequency change?

3. Draw a circle to represent the path taken by your rotating mass.Place a dot on the circle to represent your rotating washer. Add astraight line from the dot to the center of the circle,representing the radius of rotation (the string). Now label thedirection of the tangential velocity, centripetal force, and thecentrifugal “force.”

4. Use your data to find the average period for each radius. Usethis and the rest of your data to calculate a) the average velocityof your spinning mass, b) its angular velocity in rad/sec, and c)the centripetal acceleration for each radius.

5. How is the centripetal force on the revolving washer related tothe force of gravity on the hanging washers? Write an expressionthat equates the centripetal force Fc of the rotating mass to theforce of gravity on the hanging mass. Write your expression interms of m1 (revolving mass), m2 (hanging mass), T, R, and g.

6. What do you notice about your centripetal acceleration values inQuestion 4? Explain this result knowing the relationship betweencentripetal acceleration and centripetal force, given theexperimental constant 4m1 = m2.

7. Solve your expression above for the period T in terms of R andg.

8. Plug in your radius values into this equation to find theexpected frequency of rotation. Record these values in the tableabove. Were your experimental values close? How could you improvethe experiment to reduce error?

9. Use the rotational kinematics equations to calculate the angularacceleration necessary to increase the angular velocity of yourspinning mass from 10 rad/s to 20 rad/s in a time of 8 seconds.

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