Phys1_03-Friction_c56f19ac-c609-4500-b40e-80780bdc644f

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Georgia Institute Of Technology *

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2111

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Electrical Engineering

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Apr 3, 2024

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Slide 1 The Force of Friction Objectives Study how the force of friction changes with mass. Solve for the coefficient of kinetic friction between the device and the surface. Physics Overview Friction is a force that opposes the sliding of an object. There are two main types of friction, static and kinetic. Static friction deals with the force needed to start an object sliding. Static friction opposes motion until an external force is strong enough to overcome it. Once the object starts moving, kinetic friction takes over. Because a larger force is required to start an object moving than to keep it moving, static friction must be greater than or equal to kinetic friction. In this lab, the force of kinetic friction will be determined as the mass is increased. We will be attaching masses to the top of the iOLab device and securing them with tape to ensure they do not move. For this lab, we will be pushing the iOLab device on a horizontal surface. Think about what that means about the relationship between the Normal Force and the Force of Gravity. In addition, by using the equation for friction, , it is possible to determine the coefficient of kinetic friction, between the device and the surface. The coefficient of friction only depends on the materials which the two surfaces are made of. Therefore, this value should be constant even as the mass changes. If you wish for a review on the topic of friction, you can choose to watch any of these videos: TiedBlocks

StaticFriction

Slide 2 Let's try it out! Attach the screw to the force probe.

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Slide 3 Accelerometer (200 Hz) Remote 1 Ax Ay Az Time (s) 0 1 2 3 4 5 6 7 8 9 10 a (m/s²) -20 -15 -10 -5 0 5 10 15 20 ∆t: 3.67667 s μ: 0.139 m/s² — σ: 0.048 m/s² a: 0.511 m/s s: 0.00 m/s³ (r²: 0.00) μ: -9.757 m/s² — σ: 0.16 m/s² a: -35.872 m/s s: -0.02 m/s³ (r²: 0.02) μ: 0.123 m/s² — σ: 0.054 m/s² a: 0.454 m/s s: 0.00 m/s³ (r²: 0.01)   Force (200 Hz) Remote 1 Time (s) 0 1 2 3 4 5 6 7 8 9 10 Fᵧ (N) -4 -2 0 2 4 6 8 10 12 14 ∆t: 3.67482 s μ: -2.015 N — σ: 0.029 N a: -7.404 Ns s: -0.01 N/s (r²: 0.06)  Rezero sensor  Finding the "Known" Value of the Mass Watch the video below to find out how to find the mass of the device. Please note that the iOLab mass will be needed in many future labs and you should remember the procedure you've done here in order to repeat it for those labs. 01 Finding the Mass of the Device

Here are some instructions in words: Take off the plate and attach the screw instead. Turn the device so that the y-axis is pointing downwards. Press record and let it sit there for 1 second. Then use the screw to lift the device. Hold it steady. Find the average force and acceleration (in the direction) once you have picked up the device. This will give you the force due to gravity and the acceleration due to gravity, respectively. Again, since the force of gravity is in the direction, you can uncheck the and the boxes.) Using the gravitational force equation, you can find the mass. Be certain that you include a sceenshot of your own data in your lab report in the "Analysis Mode", while highlighting the region over which you wish to average the data. Be certain to extract meaningful numbers into a clear table and explain in detail how you use the measurements to calculate the mass of your iOLab.

Slide 4 Accelerometer (200 Hz) Remote 1 Ax Ay Az Time (s) 0 1 2 3 4 5 6 7 8 9 10 a (m/s²) -20 -15 -10 -5 0 5 10 15 20 ∆t: 3.67667 s μ: 0.139 m/s² — σ: 0.048 m/s² a: 0.511 m/s s: 0.00 m/s³ (r²: 0.00) μ: -9.757 m/s² — σ: 0.16 m/s² a: -35.872 m/s s: -0.02 m/s³ (r²: 0.02) μ: 0.123 m/s² — σ: 0.054 m/s² a: 0.454 m/s s: 0.00 m/s³ (r²: 0.01)   Force (200 Hz) Remote 1 Time (s) 0 1 2 3 4 5 6 7 8 9 10 Fᵧ (N) -4 -2 0 2 4 6 8 10 12 14 ∆t: 3.67482 s μ: -2.015 N — σ: 0.029 N a: -7.404 Ns s: -0.01 N/s (r²: 0.06)  Rezero sensor  Find the Mass of the Device Recall from last lab how you found the mass of the device and repeat this. If you need a refresher, you can watch the video below: 01 Finding the Mass of the Device

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Be certain to document how you performed this measurement using screenshots of your data, tables of extracted numbers (with units), and clear descriptions of how your calculations are performed.

Slide 5 Accelerometer (200 Hz) Remote 1 Ax Ay Az Time (s) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 a (m/s²) -5 0 5 10 15 20 25 30 35   Force (200 Hz) Remote 1 Time (s) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 Fᵧ (N) -4 -2 0 2 4 6 8 10 12 14  Rezero sensor  Give the Device a Push Replace the screw with the plate. Place the device with the wheels up (not in contact with the table). Give the device a push from the plate in the direction. Use Analysis mode to find the acceleration of the device after your push (Look at the picture below for more information). We are only looking at the acceleration in the direction since that was the direction of the force. Therefore, you can uncheck the and boxes to only look at . You can also increase the smoothing if you choose.

Before moving on, please consider these questions: 1. When you stop pushing on the device, it still has an acceleration. Why? 2. Using the mass and the acceleration, how can you find the force acting on the device?

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Slide 6 Procedure Please note: You will be taking data in the next 6 slides. You can return to the data you take by clicking on the proper slide number, but you MUST hit "Save & Go Next" in order to save your data. If you take data and move to a previous slide without hitting the save button, your data will be lost. Please be careful! 1. Attach a mass to the device with scotch tape as shown in the picture below. 2. On the next slide, find the mass of this new system. 3. On slide 7, give the system a push, and find the acceleration after the push. 4. Add a second mass to the top of the first and repeat again (taking data in the upcoming slides). 5. Use the force of gravity to calculate the normal force. 6. Plot the force of friction vs. the normal force in Excel and add a linear trendline. 7. Calculate for each trial (each mass) and average the values. 8. Using the slope of the force of friction vs. the normal force plot, find 9. Compare the two values of

Some Things to Consider Do not add too much mass to the system. The force probe can only withstand 10 Newtons. Always make sure you add the masses to the side of the device with the wheels. We want to make sure that the bottom of the device is always the side sliding against the surface. Do not change the table or surface you are using in the middle of the experiment!!! Measure the friction acceleration from the region AFTER the push (not before).

Slide 7 Force (200 Hz) Remote 1 Time (s) 1 2 3 4 5 6 7 8 9 10 Fᵧ (N) -8 -6 -4 -2 0 2 4 6 8 10 ∆t: 3.35500 s μ: -3.992 N — σ: 0.10 N a: -13.393 Ns s: -0.05 N/s (r²: 0.23)  Rezero sensor  Accelerometer (200 Hz) Remote 1 Ax Ay Az Time (s) 1 2 3 4 5 6 7 8 9 10 a (m/s²) -20 -15 -10 -5 0 5 10 15 20 25 ∆t: 3.35571 s μ: 0.190 m/s² — σ: 0.12 m/s² a: 0.639 m/s s: 0.02 m/s³ (r²: 0.04) μ: -9.605 m/s² — σ: 0.26 m/s² a: -32.232 m/s s: -0.07 m/s³ (r²: 0.07) μ: -1.318 m/s² — σ: 0.29 m/s² a: -4.422 m/s s: 0.19 m/s³ (r²: 0.41)   Mass Number 2 (the iOLab device with another mass added)

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Slide 8 Accelerometer (200 Hz) Remote 1 Ax Ay Az Time (s) 0 1 2 3 4 5 6 7 8 9 10 a (m/s²) -20 -15 -10 -5 0 5 10 15 20 25   Acceleration Number 2

Slide 9 Force (200 Hz) Remote 1 Time (s) 1 2 3 4 5 6 7 8 9 10 Fᵧ (N) -10 -8 -6 -4 -2 0 2 4 6 8 ∆t: 3.95298 s μ: -5.817 N — σ: 0.16 N a: -22.994 Ns s: 0.07 N/s (r²: 0.24)  Rezero sensor  Accelerometer (200 Hz) Remote 1 Ax Ay Az Time (s) 1 2 3 4 5 6 7 8 9 10 a (m/s²) -20 -15 -10 -5 0 5 10 15 20 25 ∆t: 3.94558 s μ: 0.223 m/s² — σ: 0.13 m/s² a: 0.880 m/s s: 0.03 m/s³ (r²: 0.10) μ: -9.743 m/s² — σ: 0.13 m/s² a: -38.441 m/s s: -0.01 m/s³ (r²: 0.02) μ: -0.125 m/s² — σ: 0.19 m/s² a: -0.493 m/s s: 0.01 m/s³ (r²: 0.01)   Mass Number 3

Slide 10 Accelerometer (200 Hz) Remote 1 Ax Ay Az Time (s) 0 1 2 3 4 5 6 7 8 9 10 a (m/s²) -20 -15 -10 -5 0 5 10 15 20 25   Acceleration Number 3

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Slide 11 Error Analysis Error in the frictional force It is due to the force of friction that the device slows down and comes to a stop instead of continuing to move at a constant velocity after you give it a push. Therefore, the acceleration that you find after the push has occurred is due to friction. Since you were able to find the mass of the device along with acceleration due to friction, you can use Newton's Second Law, to find the force of friction (friction is the only force acting in the direction in this case). However, the mass and acceleration values both have errors associated with them. (You can find the error in the mass in the same manner as last lab and you can find the error in the acceleration given by in analysis mode.) With the error values of both the mass and the acceleration, you can then use the multiplication/division rule from the error and uncertainty guide to find the error in the frictional force. Error bars Since you will be plotting the frictional force vs. the normal force, you will be able to include error bars on your plot. We just found out how to find the error in the frictional force in the section above. By adding custom error bars in Excel, you can include the error values you calculated as error bars. You can also find the error in the normal force by relating it to the gravitational force. Due to the fact that the device is on a flat surface, there are no other forces acting in the direction, and there is no acceleration in the direction, the normal force and the gravitational force are equal in magnitude. Therefore, by finding the error in you have found the error You can then include these as custom error bars. Finding the error in When you found the mass of the device, you used analysis mode to find the average force while holding the device from the screw. You can also use analysis mode to find the of this value. This will be the error in the gravitational force.