Unit 3 Lab Report

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Broward College *

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2048

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Mechanical Engineering

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Apr 3, 2024

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docx

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5

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Roman Yagmurov Prof. Tuero PHY2048L 2/28/2024 Unit 3 Lab: Friction Abstract: I found the coefficient of static and kinetic friction of a rubber block on a concrete surface, as well as an aluminum block on a steel surface. To do so, I used a virtual simulation, from which I recorded the values that were output by the simulation. I then graphed the data into points, with the x-axis being normal force and the y-axis being friction force. From there I used a line of best fit to average the data and then found the slope of the line, which is the coefficient of friction. I then looked online for the accepted values and compared them to my calculated values using percent error. My calculated results were: .95 for the coefficient of static friction and .71 for the coefficient of kinetic friction of rubber on concrete; and .60 for the coefficient of static friction and .47 for the coefficient of kinetic friction of aluminum on steel. The percent error for all of them was in the following order: 5.6%, -11.3%, -1.64% and 0%.
Introduction: In this lab I will be finding the coefficients of both static and kinetic for multiple combinations of objects and surfaces. I will be using different mathematical equations, as well as different sources from the internet to compare my results to their accepted values. I will be recording data and graphing it to find what I am looking for. General Principles: Friction is a force that always acts in the direction opposite to the direction of movement. It happens due to the materials’ molecular and microscopic structure, so it is invariable between objects made of the same materials. Friction is found with the use of a coefficient of friction, which quantifies how resistant a material is to movement, and the normal force, which means that friction depends on an object’s mass and weight. There are two types of friction: static and kinetic. Static friction is the friction of an object that is stationary or isn’t sliding. It is the force that needs to be overpowered in order for sliding to start, which means that the applied force needs to be greater than or equal to the force of static friction. Kinetic friction is friction that an object experiences while sliding. It is almost always less than the static friction of the object. The coefficient can be found by doing multiple trials with different weights for each of the surface-object combinations, then graphing the data, with the x-axis being normal force (N) and the y-axis being friction force (N), to find a best fit-line which basically averages the data points. Then, simply finding the slope of the best-fit line will give us the coefficient since dividing friction force by normal force will give the coefficient as per the mathematical definition of frictional forces since the equation for them is F = μ F N . Methods: Since this is a virtual lab, I will be using the website provided to “test” the different materials out. I will write down the results in a table, graph them, find a best-fit line using the point slope formula y 0 y = m ( x 0 x ) which I will use to find m since that is the slope of the line
and, by definition, the coefficient of friction. I will then find more accurate values online and compare mine to them using percent error. I will do this for multiple materials and surfaces. Analysis & Results: To find coefficient of static friction, we can use the formula F s = μ s F N and for the coefficient of kinetic friction we can use F k = μ k F N . First, I tested the maximum static and kinetic friction of a rubber block on concrete and the results are: After this test, it is evident that the coefficient of static friction is going to be greater than the coefficient of kinetic friction. From these two graphs of the data, it can be seen that the relationship between normal force and friction in general is linear, with the slope being the coefficient. For the first data set, the coefficient of static friction is μ s = .95 and the coefficient of kinetic friction is μ k = .71 . These two values are the slopes of the best-fit line of the graphed points, which means that the slopes differ. After searching the web, there isn’t a single consensus on the values for the coefficients, but they 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 0 0.5 1 1.5 2 2.5 3 3.5 4 Kinetic Friction 1B 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Static Friction 1A
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