September 19, 2016: Modeling Friction Forces

Anthony Betancourt
Lab Partner: Josh Fofrich
Professor Wolf

Lab #7: Modeling Friction Forces

Purpose:

The purpose of this lab is to introduce the student to the concept of friction forces that occur between two surfaces of different material.  Also, to be able to derive calculations relating friction forces in the lab experiments.  

Procedure:

Part 1:

1. Place large wooden board on lab table.  attach a pulley to one end hanging off the edge of the table.
2. Grab a wooden block with one side having tile flooring surface attached.  Place the tile side down on top of the white wooden boards surface.  
3. Attach string from one of block, over the pulley, and down towards the ground with a loop to hang masses from.  
4. Place slotted masses onto hanging mass in small increments until the wooden block begins to start moving.  
5. Repeat step 4 until you have successfully completed 5 trials, adding a larger mass to the wooden block in increments of 200g for each additional trial.  
6. Draw free body diagram in order to solve for the coefficient of static friction

(Setup for Part 1)

Part 2:

1. Place wooden block onto white wooden board surface with tile side down.  
2. Calibrate the force sensor prior to using it in experiment
3. Attach force sensor onto the side of the block with string.
4. Pull the block at a constant speed while running logger pro.  The data collected can be linear fit on the graph and averaged out for the force pulled the block with.  
5. Place an added mass on top of the wooden block and run experiment again with logger pro to collect the data.  Repeat until 4 trials have been completed.

Part 3:

1. Place wooden block with tile side down on the white wooden board.  
2. Utilizing your smart phone level app, tilt one end of the board up until the block begins to move.  
3. Write down the angle at which the board was raised just before the block started to move. 

(Setup for Part 3)

Part 4:

1. Place wooden white board on an angle using a lab stand to hold it up.
2. Place a motion detector at the top of the incline in order to capture the block motions as it slides down.  
3. Be sure to measure the incline and the acceleration of the block.  

Part 5:

1. Place the white wooden board down on the table top with a pulley attached to the end hanging off the table.  
2. Place motion sensor on the opposite directly behind the path of the moving block. 
3. Attach string between the wooden block and a hanging mass that is above the surface of the ground.
4. Choose a mass large enough to accelerate the block toward the edge.  
5. Utilize derived expression for kinetic friction to predict the acceleration of the system.  
6. Compare experimental results with theoretical values.  

(Setup for part 5)

Theory:

In order to determine the coefficients of friction for both kinetic and static, we need to understand the difference between the two.  Kinetic friction is present between two surfaces that are moving opposite one another. Static friction is when two surfaces are in contact but not in motion.  From free body diagrams, one can derive the equations in order to calculate these two friction forces given their specific scenarios.  In this lab, parts 1 through 4 will have its own variation of the general experiment in order to collect data regarding kinetic and static friction.  

Measured Data:

(Data Table and for part 1)

(Data for Part 2)

(Calculations for Part 3)

(Calculations for Part 4)

(Calculations for Part 5)

(graph for part 1)

(graph for part 2)

(graph for part 4)

(graph for part 5)

Analysis:

From part 1 we noticed that trying to find an exact amount of mass to hang became more trivial than expected.  Several trials had to be ran in order to get a sufficient outcome for the static friction.  For Part 2, we had better luck with determining the coefficient of kinetic friction.  The force sensor was able to give a relatively accurate reading when the block was pulled at a constant speed. Each trial was consistent and we were able to achieve a value of 0.27 for kinetic friction.  Part 3 of the lab was another success.  The iPhone level app proved to be fairly accurate enough for this part of the experiment. In part 4, some minor issues came up with the use of our motion sensor.  Fortunately, Professor Wolf came to the rescue and helped adjust the sensor to get a better reading on our block.  In Part 5 we were able to utilize all the data gathered thus far and make educated predictions to how the system would accelerate.  The correlation value on our graph for part 5 was able to reach 0.9997.  

Conclusion:

After close examination of our data we collected, the method of trying to determine the coefficient of static friction was more difficult than kinetic friction.  Ultimately our data represents well that through proper experimentation and calculations, the coefficients of kinetic and static friction can be achieved.