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1、Static and Kinetic Friction LabIntroductionThe amount of friction force (Ffr) between two surfaces in contact depend on the nature of the surfaces in contact (m) and the amount of compression between the surfaces (FN) according to Ffr = m FN Objectives Measure the coefficients of static and kinetic
2、friction for pads on a calculator cover and track. Determine if the coefficient of kinetic friction depends on weight.MaterialscomputerstringVernier computer interfaceCalculator cover with pads and block of wood with hookLogger Probalance or scaleVernier Force Sensormass setProtractormetal rampProce
3、durePart I Peak Static Friction and Kinetic Friction1.Measure the mass of the block and calculator cover and record it in the data table. 2.Connect the Dual-Range Force Sensor to Channel 1 of the interface. Set the range switch on the Force Sensor to 50N. 3.Open the file “12a Static Kinetic Frict” f
4、rom the Physics with Computers folder.4.Tie one end of a string to the hook on the Force Sensor and the other end to the hook on the wooden block. Put the block on the calculator cover with the pads facing down on the metal ramp. (see diagram below) Practice pulling the block and masses with the For
5、ce Sensor using this straight-line motion: Slowly and gently pull horizontally with a small force. Very gradually, taking one full second, increase the force until the block starts to slide, and then keep the block moving at a constant speed for another second.Metal rampCalculator cover5.Hold the Fo
6、rce Sensor in position, ready to pull the block, but with no tension in the string. Click to set the Force Sensor to zero. 6.Click to begin collecting data. Pull the block as before, taking care to increase the force gradually. Repeat the process as needed until you have a graph that reflects the de
7、sired motion, including pulling the block at constant speed once it begins moving. 7.Examine the data by clicking the Statistics button, . The maximum value of the force occurs when the block started to slide. Read this value of the maximum force of static friction from the floating box and record t
8、he number in your data table.8.Drag across the region of the graph corresponding to the block moving at constant velocity. Click on the Statistics button again and read the average (or mean) force during the time interval. This force is the magnitude of the kinetic frictional force.9.Repeat Steps 6-
9、8 for two more measurements and average the results to determine the reliability of your measurements. Record the values in the data table.10.Add masses totaling 250 g to the block. Repeat Steps 6 9, recording values in the data table.11.Repeat for additional masses of 500, 750, and 1000 g. Record v
10、alues in your data table.Part 2 Peak Static Friction for an incline1. Put the calculator cover on the horizontal ramp with 500 g mass inside. 2. Slowly increase the ramps angle of inclination to the horizontal until the box just begins to slide. 3. The largest angle at which the box does not slide i
11、s called the critical angle, qc. Measure this with a protractor and enter in the table.4. Repeat two more times. Average the results.5. Repeat 1 4 with 1000 g mass.DATA TABLEPart I Peak Static and Kinetic FrictionMass of block (kg)Peak static friction (N)AverageTotal mass (kg)Normal force (N)Trial 1
12、Trial 2Trial 3peak static friction (N)Kinetic friction (N)AverageTotal mass (kg)Normal force (N)Trial 1Trial 2Trial 3kinetic friction (N)Part 2 Peak Static Friction for an InclineCritical Angle (qc)AverageTotal mass (kg)Trial 1Trial 2Trial 3Critical Angle (qc)Analysis1.For Part I, calculate the norm
13、al force of the table on the block alone and with each combination of added masses. Since the block is on a horizontal surface, the normal force will be equal in magnitude and opposite in direction to the weight of the block and any masses it carries. Fill in the Normal Force entries for both Part I
14、 data tables.2.Plot a graph of the maximum static friction force (vertical axis) vs. the normal force (horizontal axis). Use either Logger Pro or graph paper. Include full title, axis labels and units.3.Since Fmaximum static = ms FN, the slope of this graph is the coefficient of static friction ms.
15、Find the numeric value of the slope, including any units. Should a line fitted to these data pass through the origin?4.In a similar graphical manner, find the coefficient of kinetic friction mk. Create a plot of the average kinetic friction forces vs. the normal force. Recall that Fkinetic =mkFN. Sh
16、ould a line fitted to these data pass through the origin? 5. Does the force of kinetic friction depend on the weight of the block? Explain.6.Does the coefficient of kinetic friction depend on the weight of the block?7. For Part 2, show that the maximum angle for which the box will not slide down the
17、 ramp is qc = tan-1(s) where s is the coefficient of static friction8. Using the critical angle, determine ms 9.Compare your coefficients of static friction determined in Part 1 to that determined in Part2. Discuss the values. Do you expect them to be the same or different?Static and Kinetic Frictio
18、n LabScoring RubricName(s) _ Class _1. Data Tables filled out correctly _ 15 pts2. Graph of the maximum static friction force (vertical axis) vs. the normal force. Title, fully labeled, linear fit with slope. _ 10 pts3. Stated coefficient of static friction ms from graph _ 2 pts 4. Graph of the aver
19、age kinetic friction forces vs. the normal force. Title, fully labeled, linear fit with slope. _ 10 pts5. Stated coefficient of kinetic friction mk from graph _ 2 pts6. Explained whether the force of kinetic friction depends on the weight of the block _ 2 pts 7. Explained whether coefficient of kine
20、tic friction depends on the weight of the block? _ 2 pts8. Showed that the maximum angle before slipping is given by qc = tan-1(s) _ 4 pts9. Show how used critical angle to determine the coefficient of static friction _ 3 pts10. Compared the two calculated values for the coefficient of static friction _ 2 pts Total _ 52 pts
