Static and Kinetic Friction Experiment 12a In this experiment, you will use a Force Sensor to study static and kinetic on a wooden block. A Motion Detector will also be used to analyze the kinetic acting on a sliding block. OBJECTIVES Use a Dual-Range Force Sensor to measure the of static. Determine the relationship between of static and the weight of an object. Measure the coefficients of static and kinetic for a particular block and track. MATERIALS computer Vernier computer interface Logger Pro Vernier Motion Detector Vernier Force Sensor string block of wood with hook balance or scale set PRELIMINARY QUESTIONS 1. In pushing a heavy box across the floor, is the you need to apply to start the box moving greater than, less than, or the same as the needed to keep the box moving? 2. Draw a free body diagram of the block being pulled across a al surface. 3. Using your free body diagram, show the equation that will allow you to determine your al. 4. Using your free body diagram, show the equation that will allow you to calculate normal. Physics with Computers 12-1
Dual-Range Force Sensor Experiment 12 PROCEDURE 1. Measure the of the block 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 50 N. 3. Open the file 12a Static Kinetic Frict from the Physics with Venier 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. 5. Hold the Force Sensor in position, ready to pull the block, but with no tension in the string. Click to set the Force Sensor to zero. 6. You will measure the maximum static and the kinetic as a function of the normal on the block. In each run, you will pull the block with the Force Sensor using a straight-line motion: Slowly and gently pull horizontally with a small. Very gradually, taking one full second, increase the until the block starts to slide, and then keep the block moving at a constant speed for another second. In further runs, when you change the es on the block, you will vary the normal on the block. Wooden block Mass Pull 7. Click to begin collecting data and pull as described in step 6 to gather vs. time data. 8. Examine the data by clicking the Statistics button,. The maximum value of the occurs when the block started to slide. Read this value of the maximum of static from the floating box and record the number in your data table. 9. Drag the cursor 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) during the time interval. This is the magnitude of the kinetic al. Record in data table (2 nd table). 10. Print one of your graphs for use in analysis question 1. (Pick a good one!) 11. Repeat Steps 6-9 for two more measurements and average the results to determine the reliability of your measurements. Record the values in the data table. 12. Add to the block. Repeat Steps 6 9, recording values in the data table. 13. Repeat for larger that is added to your block. Record values in your data table. 12-2 Physics with Computers
DATA TABLE Static and Kinetic Friction Mass of block kg Peak static Trial 1 Trial 2 Trial 3 maximum static Kinetic Trial 1 Trial 2 Trial 3 kinetic (When you get a particularly nice graph, print one for use in the analysis section later.) ANALYSIS 1. Inspect the vs. time graph that you printed. Determine the portion of the graph corresponding to the block at rest, the time when the block just started to move, and the time when the block was moving at constant speed. Label these sections on your graph. (One per group is fine.) 2. Still using the vs. time graph you created in Part I, compare the necessary to keep the block sliding compared to the necessary to start the slide. Do you need to adjust your answer in Preliminary Question #1 or were you correct? If you need to correct it, state what the correct answer is here. 3. On a piece of graph paper or using Logger Pro, plot a graph of the average maximum static (vertical axis) vs. the normal (horizontal axis). (Print a group copy of this graph.) 4. Since F maximum static = s F N, the slope of this graph is the coefficient of static s. Use a best fit line to find the numeric value of the slope. µ s = 5. On a piece of graph paper or using Logger Pro, plot a graph of the average kinetic (vertical axis) vs. the normal (horizontal axis). (Print a group copy of this graph.) 6. The slope of this graph is the coefficient of kinetic µ k. Use a best fit line to find the numeric value of the slope. µ k = Physics with Computers 12-3
Experiment 12 Physics Static and Kinetic Friction Lab PRELIMINARY QUESTIONS 1. In pushing a heavy box across the floor, is the you need to apply to start the box moving greater than, less than, or the same as the needed to keep the box moving? 2. Draw a free body diagram of the block being pulled across a al surface. 3. Using your free body diagram, show the equation that will allow you to determine your al. 4. Using your free body diagram, show the equation that will allow you to calculate normal. DATA TABLE Mass of block kg Peak static Trial 1 Trial 2 Trial 3 maximum static Kinetic Trial 1 Trial 2 Trial 3 kinetic (When you get a particularly nice graph, print one for use in the analysis section later.) 12-4 Physics with Computers
Static and Kinetic Friction ANALYSIS 1. Inspect the vs. time graph that you printed. Determine the portion of the graph corresponding to the block at rest, the time when the block just started to move, and the time when the block was moving at constant speed. Label these sections on your graph. (One per group is fine.) 2. Still using the vs. time graph you created in Part I, compare the necessary to keep the block sliding compared to the necessary to start the slide. Do you need to adjust your answer in Preliminary Question #1 or were you correct? If you need to correct it, state what the correct answer is here. 3. On a piece of graph paper or using Logger Pro, plot a graph of the average maximum static (vertical axis) vs. the normal (horizontal axis). (Print a group copy of this graph.) 4. Since F maximum static = s F N, the slope of this graph is the coefficient of static s. Use a best fit line to find the numeric value of the slope. µ s = 5. On a piece of graph paper or using Logger Pro, plot a graph of the average kinetic (vertical axis) vs. the normal (horizontal axis). (Print a group copy of this graph.) 6. The slope of this graph is the coefficient of kinetic µ k. Use a best fit line to find the numeric value of the slope. µ k = Physics with Computers 12-5