Friction

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Temple University *

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1021

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Mechanical Engineering

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Jan 9, 2024

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Uploaded by ProfessorMoleMaster802

Title: Friction Group 33: Van Tran, Elyse Gallagher, Shrenik Patel Experiment Date: October 3rd, 2023 Goals: The goal of today’s lab is to observe the friction at the interface of two objects. We explore the differences between static friction and kinetic friction and also how Newton’s laws apply to them. Procedure: Part I. ● Place block on wood surface ● Hook force sensor onto the block ● Identify force sensor on Capstone and create graph (force vs time) ● Zero the sensor, click record, and pull block slowly at a constant speed and force ● Weigh block ● Find average force on graph ● Draw force diagram of all forces acting on the block ● Calculate value of mk Part II. ● Draw free body diagram on inclined plane ● Follow instructions on lab manual and show how combining 2 two equations results in the final expression ms=tan0 ● Place block on inclined plane wood face down ● Tilt incline up until the block just starts sliding ● Record value of angle and use that value to calculate ms Precautions and Sources of Error : Sources of error include human error. In the first part of the lab we had to do our best to move the block at a constant speed. So the speed could have been more varied than constant during this part. Data:

Part I: Weight of Block: 390.5g or 0.3905 kg Mk ∗ mg = Fapp M k ∗ 0.3905 kg ( 9.8 m / s 2 )= ¿ 0.92 N Mk = 0.24 Part II: Free Body Diagram Fn Fg Fap p Fk

Incline angle- 25 degrees ∑ F X = N - F gy = 0 ∑ F Y = F gx - F s = 0 F gy = mgco s? F gx = mgsi n? M s = (mgsinθ)/(mgcosθ) M s =tanθ M s =tan25 M s =0.47N Questions: Free Body Diagram Fn Fg

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Question 1: When moving at a constant speed how does the magnitude and direction of the friction force acting on the block? The magnitude and direction of friction force remain constant since the object is moving at a constant speed. Question 2: How can Newton’s 3rd law be used to explain why the weight of the block is equal to the normal force acting on the block? The third law says that when two objects interact then they apply equal and opposite force on each other hence in this case normal force will be equal to the weight of the body. Question 3: Was the value of ℳ s you obtained reasonable? To support your answer, refer to the reported values here for a similar pair of materials noting that the block is wood. Our value seems reasonable since our Ms should be higher than our Mk and that is what we observed. Our M k is 0.24 while our M s is 0.47 Question 4: Why is the angle to get the block to start sliding larger than the angle to get the block to stop sliding? Referring to the graph in the figure below may help you. The difference in angles can be described as the difference in nature of static and kinetic friction. Static friction is generally stronger and requires more force to overcome, while kinetic friction is typically weaker and allows objects to slide more easily. A greater angle is needed to overcome the higher static friction and set the object in motion, whereas a smaller angle is sufficient to counteract the lower kinetic friction and bring the block to a stop. Question 5: Observe the figure below showing the force of friction on the y-axis, and the applied force on the x-axis. Indicate on the graph the following points a. Some amount of force is applied but the box remains stationary. Increasing the force slightly does not make the box move. i. Static Region b. No force is applied. The box is stationary. i. Origin c. Enough force is being applied that the box is moving. i. Kinetic Region d. Some amount of force is applied but the box remains stationary. Increasing the force slightly causes the box to start moving. i. Intersection of static and kinetic region

Question 6: When trying to stop a car on icy pavement in as short a distance as possible, is it better to slam on the brakes and skid to a stop or apply the brakes more gently and roll to a stop? Hint: What type of friction is acting between your tires and the roadway if your tires are sliding along the road? What if your tires are rolling along the road?) Briefly explain. As the kinetic friction is less, it is better to apply the brakes gently and roll to stop the car. This leads to less stopping distance and the motion of the car would be controlled. The static friction is greater than kinetic friction. Static friction is the friction that is between the tires and roadway when your tires are rolling along the road. Kinetic friction is the friction acting between the tires and roadway when sliding along the roadway. Discussion: This lab focused on Newton’s Laws once again more importantly friction. In the first part of the lab we looked at the forces involved when a wood black is placed on a wooden surface and is being pulled with a constant force. We used the formula Mk ∗ mg = Fapp and got 0.24 as our Mk . In part 2 we looked at static friction. We took our wooden block and elevated the block just enough that we were able to get it to slide. We used the angle to find our static friction. We were able to get 0.47 which is in the acceptable range from the given values. Overall our errors come from human error as we had to do everything to the best of our ability to keep things constant.