# Lab 106.docx - Kevin Pisacane Group 1 PHYS 102A-105 Lab...

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This preview shows page 1 out of 4 pages. Unformatted text preview: Kevin Pisacane Group 1 PHYS 102A-105 Lab Report LAB 106: Static and Kinetic Frictions Professor Aneer Lamichhane Lab Partners: Mohammed, Jordana, Arthur Introduction: The main goal of this lab is to study and measure the static and frictional force using a force sensor. Then, comparing that to a theoretical value obtained by a formula. Both static and kinetic friction coefficients depend only on the nature of the two surfaces in contact with each other, and are independent of the normal force exerted between the two surfaces. We are going to use this lab experiment to determine the relationship between friction force and normal force acting on an object. We will also learn how to measure the coefficients of static friction and kinetic friction between surfaces. Equations to be used 1. Fg = mg 2. Fx = Fg sin (θ) = mg sin (θ) 3. Fy = Fg cos (θ) = mg cos (θ) 4. Fnet,x = Fx - fs = 0 5. fs = Fx = mg sin (θ) 6. Fnet,y = N - Fy = 0 7. N = Fy = mg cos (θ) 8. fs, max = s N 9. s = fs, max = mg sin (θc) = tan (θc) N mg cos (θc) Procedure: Lab computer with Capstone software installed, 850 Universal Interface, Force sensor, Friction Apparatus, Friction Trays (Felt and Plastic), String, Standard set of weights, Digital scale on the counter. Setup: 1. Login in and plug in all necessary technology for the experiment. Part 1 1. Measure the mass of each empty Friction Tray. (Record) 2. Place the friction cart on the friction apparatus. The top of pulley should be of same height as the hook of the cart. 3. Put a mass in the friction cart and connect the cart to the Force Sensor with the string. 4. After you click record, slowly pull the motion sensor until the cart starts to move and continue pulling it at a constant velocity. 5. Find the static friction force (maximum) and the kinetic friction force (mean). 6. Repeat with five different normal forces for the friction tray that you selected. 7. Record the slopes, which are the static and kinetic friction coefficients. 8. Record and analyze your data. Part 2 1. Place a friction cart with a weight on a horizontal friction apparatus. 2. Slowly tilt the track until the cart starts to slide down. 3. Record the critical angle. 16° 4. Determine the static coefficient ( s ) using fs, max = tan (θc), and compare it with the one that you found in part 1. 5. Repeat and record and analyze your data. Data: Part 1: SN Mass (g) Static Friction Kinetic Friction Coef. of Static 1 195.79 0.37 0.16 0.1928 2 295.79 0.58 0.35 0.2001 3 495.79 1.13 0.68 0.2326 4 695.79 1.80 0.97 0.2639 5 895.79 2.13 1.34 0.2426 Average: Static friction-0.2275 Kinetic friction-0.1060 Part 2: Critical angle: Felt- 16: tan(16) = 0.2867 Plastic- 10: tan(10) = 0.176326981 Sample Calculations: Static coefficient=Fs/FN Static coefficient=Fs/mg Static coefficient=0.37/(0.19579*9.8) Static coefficient=0.1928 Coef. of Kinetic 0.0805 0.1207 0.1399 0.1423 0.1526 Kinetic coefficient=Fk/FN Kinetic coefficient=Fk/mg Kinetic coefficient=0.16/(0.19579*9.8) Kinetic coefficient=0.0805 Average=(SN1+SN2+SN3+SN4+SN5)/5 Average=(0.1928+0.2001+0.2326+0.2639+0.2426)/5 Average=0.2275 Percent difference=|experimental-theoretical|/theoretical*100 Percent difference=|0.22751-0.17633|/0.17633*100 Percent difference= 29% Questions: 1. The felt bottom has the largest friction coefficient, and this does relate to prior experiences, felt is like a rug surface which is much harder to push something along compared to a plastic surface. 2. As the motion begins, the object has a steadily increasing force acting upon it Midway through the motion the force begins to weaken and then stays at a constant force. 3. Yes, the normal force was used to calculate both coefficients, it is the weight pulling towards the center of earth, causing the coefficient to decrease as mass increases. 4. As mass increases, both values increase as well, causing more resistance to the force puling the object. Discussion: The main goal of this lab is to study and measure the static and frictional force using a force sensor, and to determine the relationship between friction force and a normal force. Friction is a force that always opposes the motion of an object. Kinetic friction occurs when two objects are moving against one another with some part of their surfaces in contact. When friction is strong enough to prevent an object from moving, we call it static friction. Kinetic friction opposes the motion of the object and is proportional to the normal force acting on an object. As seen from the data, the results were consistent with the theory that as mass increases, the opposing frictional forces increase as well. Therefore, the more an object weighs, the more resistance there will be if friction exists. The theoretical value was obtained from the critical angle where the cart moved without any force. The tangent of the critical angle was found to obtain the static friction coefficient. Opposite over adjacent, also tangent, means the static friction over the weight force as well. Essentially, the same value was divided by the same value for each to obtain to the coefficient of static friction. Conclusion It was concluded from this experiment that our results were not so precise. The critical angle seemed to be the issue, finding the exact angle the truck begins to move can be challenging. Also, moving the truck at a constant speed is merely impossible to do. Lastly, the technology may have also been a source of error since all the calculations were based off of values obtained from the technology. ...
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