# Physics Lab Report - What Keeps a Stopper Moving in a Circle

Topics: Force, Circular motion, Kinematics Pages: 4 (948 words) Published: February 22, 2013
What keeps the stopper moving in a circle?
Purpose: Relate the variables involved in uniform circular motion

Hypothesis: I predict that the velocity of the stopper will increase as the radius is shortened.

Rubber stopper with a hole
PVC tube or wooden spool

1. Measure the mass f the stopper and washer, m, and record it in the data and observations section. Then, prepare the experimental apparatus as shown in figure A. 2. Throughout this experiment, you will need to maintain a constant radius of uniform circular motion while ensuring that all of the centripetal force is provided by the clamp and measured on the spring scale. Practice whirling the stopper in a horizontal plane until you can keep the paper clip a short distance just below the bottom of the tube. If the paper clip touches the bottom of the tube, then the clamp is no longer supplying the centripetal force. If the paper clips rises or falls appreciably as the stopper whirls then the radius of the circle is changing.

B. Constant Radius and Variable Speed

3. With the paper clip against the tube and the string pulled taut, measure the length of the string from the top of the tube to the stopper. Record this as the radius, r, for all three data runs in 4. Whirl the stopper while maintaining a constant force reading on the scale. Once you obtain a constant force, start the stop watch and continue the whirling while monitoring the force. Stop the stopwatch after 30 rev.

5. Record your force and time in data table 1, data run 1.
6. Increase the rate of whirling while maintaining the clip just below the bottom of the tube, and observe what happens to the tension measured by the spring scale. It should increase. Repeat step 4 t this higher spring force.

7. Record your force and time in data table 1, data run 1.
8. Repeat step 6 and record the data in table 1, data run 2.

C. Contact force and Variable Radius

9. Change the position of the paper clip to decrease the radius uniform...