Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Physics 2 Lab 4: Static and Kinetic Friction (this will go in your lab notebook) Introduction: If you try to slide a heavy box resting on the floor, you may find it difficult to get the box moving. Static friction is the force that is counters your force on the box. If you apply a light horizontal push that does not move the box, the static friction force is also small and directly opposite to your push. If you push harder, the friction force increases to match the magnitude of your push. There is a limit to the magnitude of static friction, so eventually you may be able to apply a force larger than the maximum static force, and the box will move. The maximum static friction force is sometimes referred to as starting friction. We model static friction, Fstatic, with the inequality Fstatic s Fn where s is the coefficient of static friction and Fn the normal force exerted by a surface on the object. The normal force is defined as the perpendicular component of the force exerted by the surface. In this case, the normal force is equal to the weight of the object. Once the box starts to slide, you must continue to exert a force to keep the object moving, or friction will slow it to a stop. The friction acting on the box while it is moving is called kinetic friction. In order to slide the box with a constant velocity, a force equivalent to the force of kinetic friction must be applied. Kinetic friction is sometimes referred to as sliding friction. Both static and kinetic friction depend on the surfaces of the box and the floor, and on how hard the box and floor are pressed together. We model kinetic friction with Fkinetic = k Fn, where k is the coefficient of kinetic friction. In this experiment, you will use a Force Sensor and an Accelerometer to study static friction and kinetic friction on a wooden block. OBJECTIVES Use a Dual Force Sensor to measure the force of static and kinetic friction. Measure the coefficients of static and kinetic friction for a particular block in contact with several surfaces. MATERIALS computer Vernier computer interface Logger Pro Wax paper Vernier Force Sensor and accelerometer Physics with Vernier string block of wood with hook balance or scale Sand paper 12 - 1 Computer 12 PRELIMINARY QUESTIONS 1. In pushing a heavy box across the floor, is the force you need to apply to start the box moving greater than, less than, or the same as the force needed to keep the box moving? On what are you basing your choice? 2. How do you think the force of friction is related to the weight of the box? Explain. 3. Predict which surface pair will show the lowest coefficients of friction: the table surface, the sandpaper, or the wax paper. PROCEDURE Part I Starting Friction 1. Measure the mass of the block and record it in the data table. 2. Connect the Accelerometer to channel 1 of the interface, and the Force Sensor to channel 2. You should see a dual screen on the laptop screen showing both force and acceleration. 3.. Hold the Force Sensor in position, ready to pull the block, but with no tension in the string. Click to set the Force Sensor and the accelerometer to zero. 4. Click to begin collecting data. Pull the block as shown below in Figure 1, taking care to increase the force gradually. Click to begin collecting data and pull as to gather force vs. time data and acceleration vs. time data. 5. With your group, decide what the data is telling you. Think about these questions and decide on a procedure to gather the needed data to find the coefficients of both static and kinetic friction. -Do you want the block to move with constant velocity? If so, how will you know that the velocity is constant? -Where on the graph is the force due to static friction? How can you measure it? -Where on the graph is the force due to kinetic friction? Again, how can you measure it? -How many trials do you need for each surface pair to accurately characterize the force for both static and kinetic? - How will you find the coefficients of friction from that data? 12 - 2 Physics with Vernier Static and Kinetic Friction Mass Wooden block Dual-Range Force Sensor Pull Figure 1 Outline your procedure below: Data Tables: Mass of block kg Data Table 1: Peak Static Friction and Kinetic Friction on the Bare Table Fill in your data table below Physics with Vernier 12 - 3 Computer 12 Data Table 2: Peak Static Friction and Kinetic Friction on the Sand Paper Data Table 3: Peak Static Friction and Kinetic Friction on the Wax Paper Data Table 4: Peak Static Friction and Kinetic Friction on the 4th surface. Record the surface here:__________________________________ 12 - 4 Physics with Vernier Static and Kinetic Friction ANALYSIS QUESTIONS: You need to explain here how you are using the date you took to calculate the coefficients of friction, and give one example for static and one for kinetic friction, stating the formulas used. Then summarize your results in a table. Conclusion: Write a paragraph conclusion summarizing your data. Compare the results to what you might have expected when you started the lab. State any sources of error that you felt could not be eliminated entirely. Lab Notebook Requirements- This should be around 4-6 pages. Title Objectives Preliminary Questions Materials Equipment set-up. Use a diagram or photo. Procedure- enough detail for another physics student who has not done this lab. Be very specific about your data collection you should have a sketch or printout of the graphs and tell me exactly how you took data for this lab. Be specific about the number of trials you did. If you used the analysis tools in Logger Pro, be sure to tell me what you did with them. Data Tables- Use a ruler, title and number each one Calculations and Results- define how calculations were done with just one example for kinetic and one for static. Summarize your results in a results table. Conclusion- State your results here, what are the coefficients of static and kinetic friction for each one of the four surface pairs. Physics with Vernier 12 - 5