Forces Lab rev aug23(1)

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William Rainey Harper College *

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EN615474

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Dec 6, 2023

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Forces-HYBRID LAB Rev. 8/16/22 DLD Page 1 of 9 LAB Examining Force and Acceleration Objective Examine and confirm Newton’s 2 nd Law of Motion Examine the force of friction for a “frictionless” system Simulate the behavior of static and kinetic friction Equipment Lab Quest interface Mass and hanger set Air Track and air source String Motion Detector Electronic balance Glider/cart with flag Ruler or straight edge (optional) Computer (with internet access, LoggerPro, and Excel or the equivalent) Theory Recall from the pre-lab that the 2 nd Law will be examined by keeping the total mass constant. The general setup class uses the air track, as seen in the photo below. This setup has been diagramed to the left of the photo. Mass 1 is the glider/cart on top of the track. Mass 2 is labeled as the accelerating (hanging) mass at the far right in the photograph. General lab setup: Investigation 1: Fletcher’s Trolley -Using Real Data to Confirm the Second Law 1. To give you a sense of how the experiment will be conducted, you first need to watch the following videos on YouTube. You should have done this prior to completing Part 2: Pre-lab Assignment for the lab, but it wouldn’t hurt to watch them again. https://www.youtube.com/watch?v=6nqJFKS_HD8This This video demonstrates the operation of the air track to acquire the data. The only differences between the method shown in the video and the one that you will use to collect data are that a) the masses used in the video are larger and b) photogates were used in the video, but you will have a motion sensor located at the starting end of the track. https://www.youtube.com/watch?v=NKnXc8ZB-vQ This second video demonstrates the exact method you will be required to use to acquire the value of the acceleration of the cart (glider) from the collected motion sensor data. Links to both videos are also posted in Blackboard. m 1 m 2 a g

Forces-HYBRID LAB Rev. 8/12/23 DLD Page 2 of 9 LAB 2. Use the electronic classroom balance to measure the following masses. m glider = (including the flag on top and hook) Total Mass of all small moveable masses (silver and black) = Mass of hanger = Calculate the total measured mass of the system and record below. This includes the flag, hook, and total hanging mass (including the hanger). Total mass of system (measured) = (kg) 3. Turn on the air supply. Once on, please leave on for the duration of the experiment. If your air supply is used by two tracks, do not adjust or turn off the air until BOTH groups are done. 4. Attach a piece of string to the air track glider, place it over the pulley and attach a weight hanger to the other end. Choose the length of the string so that the hanging mass will hit the table before the glider hits the end of the track. 5. Attach the motion detector to the Dig/Sonic 1 port on the Lab Quest mini interface from the computer accessory box. Attach the interface to the laptop using the appropriate cable from the computer accessory box. 6. Start the computer and open Logger Pro. The program should automatically identify the motion detector and open a file on the screen to measure appropriate quantities. If the words “No device connected” appear below the tool bar on the left side of the screen, unplug your Lab Quest mini from the computer and plug it back in to see if it connects. If not, ask your instructor for assistance. 7. Before collecting data, go to the FILE menu and select “Settings” (3 rd from bottom). When it opens, change the values in the drop down menus for the number of points used in both the derivative calculations and in the smoothing calculations to 39 and then click OK. 8. Place all five of the small masses on the hanger. Place the glider onto the track and pull it close to the motion detector. Remember to keep the glider at least 15 cm from the motion detector. 9. Press Collect on the computer. Wait until you hear the detector clicking and then release the glider down the track and record the graph of its velocity vs. time. Select the appropriate straight section of the graph where the glider was accelerating by clicking and dragging that portion of the graph. Complete a linear best fit on the graph by clicking on the icon in the tool bar that looks like this . Record the acceleration in Table 1 as the slope of the velocity vs. time graph. You do not need to include the error on the value.

Forces-HYBRID LAB Rev. 8/12/23 DLD Page 3 of 9 LAB 10. Record the total hanging mass (including the hanger) and the acceleration in the Table 1. It is NOT recommended that you try the experiment with only the hook. It is too light and makes data collection difficult. 11. Move 1 g of mass from the hanger to the glider in steps. This will require shifting masses between the hanger and the glider. All of the masses MUST remain in the system at all times. Repeat your steps until you have completed ten runs with 10 different values of hanging mass. Record all of your values in Table 1. 12. Calculate the hanging weight (from the hanging mass) and add that information to Table 1. Show a sample calculation below (equation, substitution with units, answer). Table 1: Acceleration of the Glider Hanging Mass (kg) Hanging Weight (N) Acceleration (m/s 2 ) 13. In Excel (or a similar program) create a graph of Accelerating Force vs. Acceleration and apply a linear best fit line to the data. Use your equation from question 2 Activity 2 in the pre-lab handout to help you fill in the following blanks with the appropriate information. let y = Eq'n in y mx b   form: let x = Slope from equation = Slope from graph = Intercept from equation = Intercept from graph = Total System Mass = Frictional force =

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Forces-HYBRID LAB Rev. 8/12/23 DLD Page 4 of 9 LAB Insert your graph (with its corresponding data table) here or attach it at the end of the lab for submission. 14. a) How did you determine m tot from the graph? b) Compare the m tot measured by the balance (and calculated in #1) with the m tot found using the graph. You should calculate either a percent error or a percent difference-which one of these is the correct calculation in this case and why? Answer the question and show all of your work (equation, substitution with units, answer) in completing the appropriate calculation. 15. How well does the value for the total mass that you determined from the graph appear to represent the total mass of the system? Use numbers and references to the data presentation. Explain your answer completely.

Forces-HYBRID LAB Rev. 8/12/23 DLD Page 5 of 9 LAB 16. a) How do you determine the estimated average force of friction? b) Does the estimated friction seem reasonable? Why or why not? Explain. c) Should the algebraic sign on the frictional force be positive or negative? Explain your answer completely. 17. a) Redraw your free body diagrams from the prelab, question 1 Activity 2. Using the average frictional force you determined from your graph , calculate the approximate coefficient of friction for the system for the cases listed in b) and c). ( Hint: what is your normal force?) Show all your work (equation, substitution with units, answer) in the space below. b) The case when all of the small masses are on the hanger (highest m 2 ). c) The case when the lowest mass was on the hanger (lowest m 2 ). d) Calculate the percent difference between these two values. Knowing this information, is it reasonable to determine an average value for the frictional force on the system from your graph? Explain your answer completely. Trolley/cart Hanging mass

Forces-HYBRID LAB Rev. 8/12/23 DLD Page 6 of 9 LAB 18. Think carefully about this experiment. As always, there were many opportunities for experimental errors to influence your data and results. Identify the 2 errors that you feel MOST influenced your results for confirming the mass of the system and determining the average frictional force. Complete the table for those 2 errors. The columns correspond to the questions you have been answering in previous labs. If your answers do not fit in the space provided, please expand the table or make your own. Complete Description of Error Type of Error (Systemic or Random) Influence on Data and/or Results Suggestion for Mitigation

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Forces-HYBRID LAB Rev. 8/12/23 DLD Page 7 of 9 LAB Investigation 2: Examining Friction (Extra Credit) 18. Open the simulation at http://www.thephysicsaviary.com/Physics/Programs/Labs/ForceFriction/index.html 19. Press BEGIN and set your mass to be between 400 and 600 grams by clicking on the red arrows. Record your value here and calculate the normal force on the block. Show all your work (equation, substitution with units, answer) to the right. Mass____________________ F N ______________________ 20. There are 6 surface combinations to test. You will test all of them so you may start with whichever one you like. You select your surface combination by clicking on the words “Type of Surfaces.” Once you have made your selection, press the START button and observe the force on the monitor as the hand pulls the force probe. Scroll down on the screen to see the graph that should look something like the graph at the top of the next page. 21. Find the highest point on the graph. This will be the point of maximum static friction. Determine a best estimate of this force value and record it in Table S1 in the appropriate location. You may find a straight edge or ruler helpful. 22. The graph becomes a constant when the friction changes from static friction to kinetic friction. Determine a best estimate for the kinetic frictional force from the graph and record it in Table S1 in the appropriate location. Again, you may find a straight edge or ruler helpful. 23. Repeat this process for the other 4 surface combinations. You need to press RESET before each new trial.

Forces-HYBRID LAB Rev. 8/12/23 DLD Page 8 of 9 LAB 24. Using your understanding of the relationships for determining the static and kinetic frictional forces, determine the coefficients of friction for each type of friction for each surface combination. Show sample calculations (equation, substitution with units, answer) for ONE of your surface combinations here. Surface combination selected: ___________________________ Finding Coefficient of Static Friction Finding Coefficient of Kinetic Friction Table S1: Frictional Forces and Coefficients Surfaces Maximum F of Static Friction (N) Coefficient of Static Friction Average F of Kinetic Friction (N) Coefficient of Kinetic Friction Wood on Lab Table Rubber on Ice Aluminum on Steel Glass on Glass Graphite on Graphite Rubber on Concrete

Forces-HYBRID LAB Rev. 8/12/23 DLD Page 9 of 9 LAB 25. The accepted value for the coefficient of static friction for aluminum on steel is 0.61; for kinetic friction, the coefficient is 0.47. Calculate the percent error between your values for these coefficients and the accepted values, showing all your work (equation, substitution with units, answer) below. Coefficient of Static Friction Coefficient of Kinetic Friction 26. Do you think the simulation gave a realistic representation of the behavior of friction? You should incorporate your knowledge of friction from lecture and your results from question 25 in giving a complete response, just stating % errors is not sufficient.

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