Lab 4

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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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docx

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Lab 4: Friction Goals The goals of the experiment were to understand Newton’s Laws and to understand the differences between static and kinetic friction. It was also important to understand and interpret the graphs of applied and friction forces. Procedure To start the experiment the force sensor needed to be calibrated to the Pasco Capstone software. To test for a force sliding at a constant velocity, a block was placed, wood faced down, onto the wood surface. Using the hook on the force sensor, it was attached to the block by string and pulled to create a graph of force v. time. To test for static friction the wood surface was set to an angle and slowly made steeper until the block slid down the plane. Error and Precautions There were multiple sources of error that have had an impact on the way that the results came out. One way to minimize problems during the experiment was making sure that the string remained parallel with the block of wood as well as not deviating higher or lower than the hook attached to the wooden block. Another aspect of it would be making sure that the force sensor works properly as sensors tend to be sensitive to drops. Making sure that the sensors are calibrated would make the forces more accurate. Results m k = T mg = 0.95 0.4312 kg ⋅ 9.8 = 0.225 kg Questions Question 1 . When moving at constant speed how does the magnitude and direction of the friction force compare to that of the force you apply to the block?

When moving at a constant speed the magnitude and direction of the friction force compares to that of the force applied to the block in that the friction force is equal to magnitude that is put in. The direction though moves in the opposite direction. 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? In Newton’s 3 rd law, it states that for every action there is an equal and opposite reaction. If block A exerts a force on block B, block B will also exert the equal and opposite reaction to block A. The force acting on the block is equal to the force of the weight because their equal forces being acted upon each other and hence and exerted on with the same force. Question 3 . Was the value of µS 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 The value of our µS is 0.225 which is a reasonable outcome. Similar values of dynamic wood to wood values are between .2-.4 and so we are in the respective values. 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 larger an angle is, the larger the sliding will be, and thus it will be harder to stop sliding the larger an angle is. Furthermore, it takes a larger angle for an object to move rest as opposed to stopping an object or the block from sliding. This is since friction is being added to the object or block as it slides, and it loses energy because of moving. 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. B. No force is applied. The box is stationary. C. Enough force is being applied that the box is moving. D. Some amount of force is applied but the box remains stationary. Increasing the force slightly causes the box to start moving.

Question 6. When trying to stop a car on icy pavement for 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. When stopping a car, it is better to gently press the brakes and try to roll to a stop because of the type of friction applied during the different stopping methods. When the car rolls to a stop, there is static friction between the car and the road. It is usually greater than kinetic friction which will allow greater traction to the surface of the road. Discussion The Expected and the actual results were the same as both were expected as the experiment went on. Through each of the processes such as measuring the force or measuring the force at an angle is each of the results remained the same. The results from the different experiments are Trial 1: 18%, Trial 2: 14, Trial 3: 15%.The reproducibility is very similar as the experiment can be redone with different forces resulting in longer or shorter times giving approximately the same answer as the experiment would go on. The sources of error may have had a negative effect on the way that the results came out. If the string was not parallel with the board or if the tension was not maintained throughout the entire process the results may be a bit different from what was expected to be.

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