Lab Report #3

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Thomas Edison State College *

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Dec 6, 2023

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LAB EXERCISE 3 Kennedy 1 Lab Exercise 3: Friction Kaylyn A. Kennedy Thomas Edison State University PHY-1280-OL009 Professor Robert Hill September 17, 2023

LAB EXERCISE 3 Kennedy 2 Lab Exercise 3: Fcceleration 1. Introduction The purpose of this lab is to investigate the relationship between static and kinetic friction forces. Friction is a force that opposes the relative motion of two objects. It is caused by the relative roughness of the surfaces of the objects. The outcome of this experiment should show a real-world example of these friction forces at work, proving that it takes more force to start an object’s movement than to keep it moving. 2. Methods A. Preparation and Setup ○ Each iteration of the trial was performed with a different surface combination: Table 1 was performed with the large side of the wood only block, Table 2 was performed with the small edge of the wood only block, Table 3 with the glass side of the wood/glass/sandpaper block, and Table 4 with the sandpaper side of the wood/glass/sandpaper block. All iterations were performed on a flat, finished wooden table top with a standard 12 fl. oz can on top of the blocks. Each block was pulled by a spring scale to get force measurements, taken in Newtons(N). Photos below of each setup: Figures: Figure 1: Wood only block, on large side. Figure 2: Wood only block, on small side

LAB EXERCISE 3 Kennedy 3 Methods(cont.) Figure 3: Wood/glass/sandpaper block, on glass side Figure 4: Wood/glass/sandpaper block, on sandpaper side B. Static and Kinetic Friction Measurement ○ These measurements were performed by pulling each apparatus five times and marking the force required to begin movement. Then, the action was repeated five times and force was marked when the object reached a constant speed. Results for these experiments are recorded in the tables below. 3. Data -All Forces represented are in Newtons -Mass of Block/Can apparatus in Tables 1 and 2 equal 403.1g therefore, F N =mass(kg)*9.8m/s Tables 1 and 2: F N = 3.95 N -Mass of Block/Can apparatus in Tables 3 and 4 equal 432.8g therefore, F N =mass(kg)*9.8m/s Tables 3 and 4: F N = 4.24 N

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LAB EXERCISE 3 Kennedy 4 Data (cont.) Table 1: Wood/Wood, Larger surface of wooden only block. Force Static Friction (F s ) Force Kinetic Friction (F k ) Coeff. Static Friction μ s =F s /F N Coeff. Kinetic Friction μ k =F k /F N Trial 1 1.25 1.20 0.316 0.304 Trial 2 1.20 1.15 0.304 0.291 Trial 3 1.20 1.10 0.304 0.077 Trial 4 1.20 1.15 0.304 0.291 Trial 5 1.25 1.10 0.316 0.278 Average 1.22 1.14 0.309 0.248 Standard Deviation 0.027 0.042 0.007 0.096 Table 2: Wood/Wood, Smaller surface of wooden only block. Force Static Friction (F s ) Force Kinetic Friction (F k ) Coeff. Static Friction μ s =F s /F N Coeff. Kinetic Friction μ k =F k /F N Trial 1 1.30 1.00 0.329 0.253 Trial 2 1.45 1.15 0.367 0.291 Trial 3 1.40 1.20 0.354 0.304 Trial 4 1.45 1.20 0.367 0.304 Trial 5 1.35 1.10 0.342 0.278 Average 1.39 1.13 0.352 0.286 Standard Deviation 0.065 0.084 0.017 0.021

LAB EXERCISE 3 Kennedy 5 Data (cont.) Table 3: Wood/Glass, Glass surface of multi-surface block. Force Static Friction (F s ) Force Kinetic Friction (F k ) Coeff. Static Friction μ s =F s /F N Coeff. Kinetic Friction μ k =F k /F N Trial 1 0.85 0.65 0.200 0.153 Trial 2 0.90 0.70 0.212 0.165 Trial 3 1.00 0.70 0.236 0.165 Trial 4 0.80 0.70 0.189 0.165 Trial 5 0.90 0.65 0.212 0.153 Average 0.89 0.68 0.210 0.160 Standard Deviation 0.074 0.027 0.017 0.006 Table 4: Wood/Sandpaper, Sandpaper surface of multi-surface block Force Static Friction (F s ) Force Kinetic Friction (F k ) Coeff. Static Friction μ s =F s /F N Coeff. Kinetic Friction μ k =F k /F N Trial 1 1.70 1.40 0.401 0.330 Trial 2 1.60 1.30 0.377 0.307 Trial 3 1.60 1.30 0.377 0.307 Trial 4 1.55 1.20 0.366 0.283 Trial 5 1.65 1.40 0.389 0.330 Average 1.62 1.32 0.382 0.311 Standard Deviation 0.057 0.084 0.013 0.020

LAB EXERCISE 3 Kennedy 6 4. Conclusion Through this experiment, I learned that friction is a force that directly correlates to the materials in contact. The coefficient of friction is a measure of how much friction there is between two surfaces. It is calculated by dividing the force of friction by the normal force. During this experiment, I had some issues conceptualizing what the coefficients of friction meant at first. However, I was able to understand them better after doing the experiment and comparing the values of the two in each iteration of the experiment. I also confirmed that the coefficient of static friction is always greater than the coefficient of kinetic friction, meaning it does take more force to start an object’s movement versus keep it moving. Additionally, I learned that the coefficient of friction depends on the materials that are in contact. For example, the coefficient of friction between wood and wood is greater than the coefficient of friction between wood and glass. Overall, I found this experiment to be very informative. I learned a lot about friction and how it works. 5. Questions 1. What is the mass of the system made of the wooden block and the soda can (or the other object that you are using)? a. Mass of wood only block: 403.1 g or 0.4031 kg b. Mass of wood/glass/sandpaper block: 432.8 g or 0.4328 kg 2. Convert the mass measured in Question 1 to its weight in Newtons. This is the value of F N that will be used in the calculations for the tables. a. Wood only block: F N = 3.95 N b. Wood/Glass/Sandpaper block: F N = 4.24 N 3. Study the results from Table 1 and Table 2. What can you conclude about these results? a. From the results of Tables 1 and 2 I can conclude two things. The first is that there is more force required to overcome friction when there is less surface area to dispel the weight of the object. This evidenced in the greater force required to begin to move(static force) the wood only block when it was on the smaller side vs. larger side. This is also evidenced in the higher friction coefficients for both static and kinetic friction. These higher coefficients exhibit that there is more force required to move the block when it is on its side vs. when it lays flat. The second conclusion evidenced by Tables 1 and 2 is that both setups, regardless of block orientation, required more force to begin to move than to keep moving. This is evidenced by higher static friction values than kinetic friction values.

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LAB EXERCISE 3 Kennedy 7 Questions(cont.) 4. Using the data from the same tables, do you think that the ratio of μ k to μ s is constant in both cases? If so, what do you think this indicates? a. I believe that the ratio of μ k to μ s is constant in both cases. When compared, the ratio of both(μ k tables 1 and 2, μ s tables 1 and 2) are 0.878 and 0.867 respectively. This indicates to me that regardless of the setup, flat or narrow edge in contact with the table when dragged, the coefficient of kinetic friction will be less than that of the coefficient of static friction. This means less force is required to keep an object moving when it is already moving versus beginning its movement from rest. 5. Studying the standard deviation data from all the 4 tables, which experiment do you think is the most reproducible? Why? a. The experiment that I consider most reproducible is the first, large lfat side of the wood only block. I came to this decision due to the fact it has the lowest standard deviation for the set of static friction force measurements as well as the second lowest standard deviation for kinetic friction force measurements. If considered for repeatability separately, Table 1 would be most repeatable for static friction force and Table 3 for kinetic friction force due to having the smallest standard deviations for those values. 6. In general, how does the coefficient of static friction compare to the coefficient of dynamic friction? a. The coefficient for static friction is generally larger than the coefficient for kinetic friction. This further exemplifies that more force is required to overcome friction when an object is at rest versus when it is already moving. 7. In designing machinery, would we prefer to use materials with larger or smaller coefficient of friction? Explain your reasoning. a. We would prefer to use materials with smaller coefficients of friction. This enables less work to be wasted on overcoming friction forces and used instead to perform the machinery’s purpose, cutting on costs and increasing efficiency.

LAB EXERCISE 3 Kennedy 8 Questions(cont.) 8. In driving a vehicle, would you prefer to use materials for the contact between the wheels and the road with larger or smaller coefficient of friction? Explain your reasoning.\ a. When driving, I would prefer to use materials that are higher in their value of friction coefficient for the contact between the wheels and the road. Without friction, between the car wheels and the pavement, the work of the wheels and drive train of the car can not make the car move. Therefore, a higher value allows the work of the drivetrain to actually move the car, making it more desirable to have a higher coefficient of friction for that material.