LAB05 - This lab is one of the weekly labs that you must complete. PDF

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This lab is one of the weekly labs that you must complete....

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PHYS 172

LAB 05

SPRING 2021

Friction Forces: Static and Kinetic LAST NAME (ALL CAPS): ANNEPU_____________ FIRST NAME (ALL CAPS) _SRIKEERTHAN________________ PUID:_32511138______ LAB Section DAY _FRI_______ LAB Section TIME _7:30-9:20____ LAB GROUP#_12__ (Asynchronous Students: for DAY and TIME, please type DIST)

Learning Goals After completing this activity, you should be able to:    

Distinguish between the static friction force and the kinetic friction force acting on the same object; Calculate the coefficients of static and kinetic friction; Use while loops in VPython to simulate the motion on an inclined plain; Connect the physical experiment and the computational model for the uniform motion with friction.

Equipment Needed The iOLab kit (with the hook), a string, a computer with the USB port and the internet connection.

Part 1: iOLab Experiment 

Take the two-sticky felts (red rectangles) which come with your iOLab kit. Peel off the paper cover and stick them on the back of the iOLab cart (see the figure below):

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Screw the hook into the iOLab cart for measuring force and tie a string to it. Set up the iOLab cart on a flat surface such as the top of a table. The surface must be in contact with the iOLab cart felts. Interface the iOLab cart with the computer. Select the ‘Force’ sensor in the iOLab application (iOLab cart must be ON) Click the ‘Record’ button and START TO PULL VERY VERY SLOWLY the string tied to the iOLab cart, so that the cart starts to move and continues moving with (approximately) a constant speed. YOU SHOULD PULL EXTREMELY SLOWLY. Suggestion: Close your eyes, so that your human senses are most finely tuned to the force you are applying with your hand. Slowly and very gently keep increasing the force until it starts to move with constant velocity. Then try to keep that constant motion for a while.

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You should get a graph similar to the one shown on the figure below:

If your graph is inverted with respect to the x-axis, use the ‘Reverse y-axis’ tool of the iOLab application. That tool appears when you click on the left bottom button of the plot and expand the toolbar (see the figure below).

Remember that you can zoom in/out your graphs in the iOLab application.

TAKE A SCREENSHOT OF THE GRAPH. PASTE IT BELOW.

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SHARE YOUR DATA WITH YOUR GROUP MEMBERS. Pleae note that the TAG NAME for your shared data is in this format: 'LAB GROUP'(as given in the "L-000_00" format) + ' LAB #' (e.g. "LAB04" for this week) E.g. if you are in Lab section L-052 and Group 7, the TAG NAME for ALL data that you share for this lab will be L-052_07+LAB04 [For those students who do not have the iOLab kit because you are outside the U.S./Canada, your Lab Grader GTA will share data with you. But you do NOT need to share it with your Group.] SEE LAB Data Sharing Instructions provided on Brightspace. Go to Content (top menu) > LAB Data Sharing (side bar) Q01: Looking at your Force vs Time graph, which part of the graph (i.e. time interval) corresponds to static friction? Which part corresponds to kinetic (a.k.a. sliding) friction? Why? Explain. Hint: recall the definitions of the static and kinetic friction forces. The beginning of the graph corresponds to the static friction. To be exact, from the x-intercept on the y-axis to the yintercept on the x-axis, the distance tells us the force needed to start moving the object

Q02: What is the maximum value of the static friction force in your graph? Explain how you obtained that number and comment on its precision. The slope of the graph will give us the friction coefficient, and if we track the graph to before the cart begins to move, the static friction coefficient is 0.49. If we multiply this by the normal force of the cart (which is 9.8 times the mass 0.203kg), we can conclude that the static friction force is 0.974806 N.

Q3: From your graph, estimate the approximately constant value of the kinetic friction force. To get the average value of a portion of a graph along the y-axis, you can use the tool shown below. With that tool activated, you can select the graph segment and it will show you the statistical data about that segment. Among that data, the first quantity denoted ‘𝛍’ is your average value (along the axis Y).

The slope of the graph will give you the kinetic friction coefficient. The kinetic friction coefficient of this lab is 0.131. If we multiply this by the normal force of the object, we can find out that the kinetic friction force of this cart is 0.2606114 N.

Q04: In this experiment you were required to keep the speed of the cart constant after it starts moving. If that speed indeed was constant, then what is the reason that the force on your graph was not zero? Page 3 of 10

Because if the net force is not zero, then the acceleration is not zero, so the speed should not stay constant. Is this a contradiction? Explain your reasoning. The force graph was not 0 due to human error. In a perfect experiment, there would be no acceleration, and the Net Force of the cart would equal 0. Because there is no net force, the cart does not accelerate, and instead, keeps moving with a constant velocity.

Q05: Use the iOLab cart to measure its own weight. What is the mass (in kg) of the cart? 0.203kg

TAKE A SCREENSHOT OF THE GRAPH YOU USED TO MEASURE THE WEIGHT OF THE iOLab CART. PASTE IT BELOW.

Q06: Use the results in Q2, Q3, and Q5 to calculate the values of the coefficients of static and kinetic friction. Show your calculations in detail. The slope of the graph will give us the friction coefficient, and if we track the graph to before the cart begins to move, the static friction coefficient is 0.49. If we multiply this by the normal force of the cart (which is 9.8 times the mass 0.203kg), we can conclude that the static friction force is 0.974806 N. Fstatic = 0.49 * 0.203 * 9.8 = 0.974806 N.

The slope of the graph will give you the kinetic friction coefficient. The kinetic friction coefficient of this lab is 0.131. If we multiply this by the normal force of the object, we can find out that the kinetic friction force of this cart is 0.2606114 N. Fstatic = 0.131 * 0.203 * 9.8 = 0.2606114 N.

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Mini-Challenge Use the iOLab cart and what you learned above about how to find the coefficients of friction and test these hypotheses:  (How) Does the coefficient of friction depend upon the mass of the object?  (How) Does the coefficient of friction depend upon the surface area of contact? Q07: Discuss with your team the design an investigation to find the answer the two questions above. Describe the experiment(s) you will perform. NOTE: You must clearly identify in your experiment the following:  independent variables (IVs) [i.e. measurable variables you will change]  dependent variables (DVs) [i.e. measurable variables that change as a consequence of changes to IVs]  controls [i.e. measurable physical quantities that you will ensure you do NOT change between trials.] Friction is a contact force when two surfaces interact. Friction only depend on the coefficient of friction and the normal force which is dependent on the mass. However, the coefficient of the friction force does not depend on either the mass or suraface area of the object involved. Independent variables – mass, surface area Dependent variables – the friction force Controls – velocity and acceleration of the cart that is being pulled Floor – the object that the cart is sliding on top of will not change

Conduct the experiment(s) that you planned above and collect the data necessary to answer the two questions above. Q08: Describe the results of the experiment(s) you conducted including the data collected and analyzed results. In order to determine if the mass has a result on the coefficient of friction, we will run the same experiement again with different masses. I hypothesize that when the mass increases, the normal force will increase, therefore increasing the friction force, but not the coefficients of the forces. To complete this trial, we can run the exact same experiement as before, but instead stack on extra weight on the iolab cart and measure.

TAKE A SCREENSHOT OF THE EVIDENCE (GRAPHS, CALCULATIONS, DRAWINGS, ETC.) YOU WILL USE AS SUPPORT OF THE CLAIMS YOU WILL MAKE TO ANSWER THE QUESTIONS ABOVE.

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In this graph, I have completed the same experiement, but with different masses. Visually, the different test trials resemble the same outcome, with the force applied being minimally different as that is due to human error. With an increased weight, you can see that the Force still is aroud the same value, as the accelleration is still 0 in each of these trials. Though there is a higher friction force due to there being more mass impacting the normal force it is multipled to, the coefficient of friction remains the same, and can be seen when highlighted by the slope tool.

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SHARE YOUR DATA WITH YOUR GROUP MEMBERS. Pleae note that the TAG NAME for your shared data is in this format: 'LAB GROUP'(as given in the "L-000_00" format) + ' LAB #' (e.g. "LAB04" for this week) E.g. if you are in Lab section L-052 and Group 7, the TAG NAME for ALL data that you share for this lab will be L-052_07+LAB04 [For those students who do not have the iOLab kit because you are outside the U.S./Canada, your Lab Grader GTA will share data with you. But you do NOT need to share it with your Group.] SEE LAB Data Sharing Instructions provided on Brightspace. Go to Content (top menu) > LAB Data Sharing (side bar) Q09: What is your conclusions about each of the two questions above? Remember that any claim you make must be accompanied by a reasoning supported with evidence. Friction is a contact force when two surfaces interact. Friction only depend on the coefficient of friction and the normal force which is dependent on the mass. However, the coefficient of the friction force does not depend on either the mass or suraface area of the object involved. The coefficient in no way was impacted in the experiment creates by me. As seen in the graphs above, the coefficient of friction stays the same.

Q10: Discuss with your team the conclusions you got and evaluate the strength of the evidence you presented to support your arguments. My evidence and argument can be supported by multiple sources on the internet. Because of this, I believe that my evidence and claims are very strong.

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Part 2: GlowScript Simulation Go to www.glowscript.org. In your Public folder, create a new program called “Friction” Copy and paste the code from the following link in “Friction”: https://www.glowscript.org/#/user/phys172vpython/folder/LAB6/ This program simulates the motion of a cart sliding down the inclined plane (ramp). It takes into account the force of friction between the cart and the surface of the ramp when performing the update equations. Q11: Run the program “Friction” and explain how it is possible that the speed stays constant while the cart is sliding down the ramp? This is possible if the x-component force of the cart going down is equal to the friction force in the opposite force. The will result in a Net Force of 0, and result in 0 acceleration.

Q12: What will happen if you change the magnitude of the initial velocity of the cart (“CartInitVelMag”) to zero? What does happen when you actually change it and run the program? If it were to start at 0 for the velocity, the cart should speed up over time and result in a faster final speed than initial speed. Instead, the x component of the gravitational force is not greater than the static friciton force, and the block does not move.

Q13: Change the static and kinetic coefficients of friction in the program with the values that you obtained experimentally in Part 1. They are called as “CoeffStatMax” and “CoeffKinet” in the “Main Parameters” section of the program. RUN THE PROGRAM, TAKE A SCREENSHOT OF THE GRAPHS AND PASTE IT HERE.

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Q14: Discuss with your team how to adjust the parameters of height and base of the ramp, such that you can get again a constant speed when you run the program using your experimental values of the friction coefficients. If you increase the height and base of the ramp, you can make it so that the x-component of the gravitational force equals the friction force. Once it is equal, the object will slide down the ramp as the component is higher than the static friction force, but equal to the kinetic friction. This makes it so that the acceleration is 0, and speed is constant.

Q15: What are those new adjusted parameters (the height and base of the ramp)? Show clearly your calculations. Height: 0.25 –> 0.30 Base: 1.0 –> 2.325

RUN THE PROGRAM AND TAKE A SCREENSHOT OF THE GRAPHS YOU GOT. PASTE IT BELOW.

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Q15: Copy below from your browser, the URL of your program edited. Remember to keep the folder PUBLIC. This will allow your TA to see your code. https://www.glowscript.org/#/user/sriannepu/folder/Lab5/

LAB Group Members’ Signatures/Typed Names (Make sure all agree to “sign off” on work) Anna Popkov Bennett Clark Srikeerthan Annepu Tylor Rauh William Mandeville

BEFORE LEAVING, EACH PERSON IN GROUP MUST  Get signatures/typed names of every LAB Group member in the boxes on the left OR type in their name.  If you have printed it off, take photos of each page, and combine them into a single PDF. If you have been working in the Word file as is, then simply save it as PDF. Each person MUST upload THE SINGLE PDF File your LAB worksheet on Brightspace by 11:59 PM SATURDAY See Syllabus for LATE POLICY

ASYNCHRONOUS STUDENTS: Please paste your entire Discussion Board here (or a link to Discussion video here)

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