Name: Partner: K/U /39 T/I /50 C /102 A Purpose: What is the relationship between the magnitude of the force causing the acceleration and the frequency of revolution of an object in uniform circular motion? Hypothesis: Derive the relationship between the frequency of rotation of the stopper and the weight of the suspended mass. (Hint, start with Newton s second law) /5 T/I Apparatus: a plastic tube with smooth ends one holed rubber stopper metal masses metre stick approx. 1 metre of fishing line masking tape balance goggles Procedure: 1. Measure and record the mass of the stopper (with uncertainty). 2. Attach the rubber stopper to one end of the fishing line. 3. Thread the fishing line through the plastic tube as shown by your teacher 4. Attach the first metal mass to the other end of the fishing line and record its mass in the table on the next page. 5. Place a piece of masking tape onto the fishing line below the tube so that the length of fishing line from the top of the tube to the bottom of the stopper is 75 cm. K/U /5 T/I /2 C A Page 1 of 10
6. Put your goggles on. 7. Twirl the stopper above your head in a horizontal circle with uniform radius at uniform speed in such a way as the hanging mass remains at a fixed height and the masking tape remains a fixed distance from the bottom of the tube. Things to note: the masking tape must not remain in contact with the bottom of the tube the radius must be the same for each trial. 8. Measure and record the time it takes for the stopper to complete 10 revolutions. 9. Repeat step 7 and 8 twice more. 10. Repeat steps 4 through 9 using progressively higher hanging mass. Observations: Mass of rubber stopper: Radius of circular path: Mass (gm.) Times for 10 Cycles (s.) Trial #1 Trial #2 Trial #3 K/U T/I /12 C A Page 2 of 10
Analysis: Notes: 1. When writing up the lab, you must record answers to the analysis questions in full sentences. 2. When references have been used, they must be properly cited at the bottom of the page they are quoted on. 1a. Calculate the weight in Newtons that corresponds to each mass and the frequency of rotation (including uncertainty) and record in the below: Force (N.) Modified Force ( ) Frequency (Hz.) Sample calculation of weight /20 A /5 A K/U T/I /12 C /25 A Page 3 of 10
Sample calculation of frequency including uncertainty /10 A 2. Plot a graph of the frequency (the dependent variable) vs. Force (the independent variable) on the graph paper on the page 5. 3a. Using the graph from step 2 and your hypothesis, determine the proportionality statement between the force and frequency. b. Modify the independent variable using the proportionality statement from step 3. Show the sample calculation below with uncertainty: /10 A 4. Draw a new graph that forms a straight line on the graph paper on page 6. 5a. Calculate the slope of the straight line graph obtained. This value represents the experimental value of the proportionality constant between f and F. /5 A K/U T/I /4 C /25 A Page 4 of 10
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b. Calculate the expected value of the proportionality constant between f and F. /6 A c. Calculate the percentage error in your slope. /6 A Discussion: 1. Discuss your hypothesis, your results and any discrepancies. /6 TI K/U /6 T/I /6 C /12 A Page 7 of 10
2. Describe the sources of error in this experiment, as well as ways you tried to minimize them. /6 TI 3. Discuss the controlled variables used in this lab if any. /4 TI Synthesis: 1. Discuss how this experiment illustrates all three of Newton s three laws of motion. /6 T/I K/U /16 T/I /6 C A Page 8 of 10
2. Discuss the difference between centripetal and centrifugal force. /6 T/I 3. Discuss what happens to the internal forces when the frequency of rotation of a spinning object increases. Include in your discussion a treatment of why this happens and what can be done to prevent structural failure of the spinning device. /6 T/I Conclusion: What is the relationship between the frequency of revolution of an object in uniform circular motion and the magnitude of the force causing the acceleration? /4 C K/U /12 T/I /8 C A Page 9 of 10
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