Measuring the coefficients of static and kinetic friction
In this laboratory you will measure the coefficient of static and the
coefficient of kinetic
friction for a wood block and a feltcovered block in contact with a metal
track. A force sensor is mounted on a cart which is attached to the
block. The force sensor measures the applied force. The mass of the block,
cart, and sensor is given in the video clip.
Open a Microsoft Word document to keep a log of your procedures and your results. This log will form the basis of
lab report. Address the points highlighted in blue.
Answer all questions.
Experiment 1
Find the coefficient of static friction.
You will examine two video clips. By stepping through these clips frame by frame
you
will determine the applied force needed to overcome the force of static
friction. As the magnitude of the applied force becomes greater than the
magnitude of the maximum force of static friction the blocks will
accelerate. Using f_{s}(max) = μ_{s}N
and N = mg,
you will determine μ_{s} for the wood block and the feltcovered block.
Procedure:
To step through video clips framebyframe click the
buttons below. The "Video Analysis" web page
will open.
Construct a table as shown below. Insert this table
into your log.
surface 
f_{s}(max) (N) 
mass (kg) 
normal force (N) 
c. of static friction μ_{s} 
wood 




felt 




Experiment 2
Find the coefficient of kinetic friction.
You will examine two video clips.
You will determine the position of the block in each clip as a function of time by stepping through the video
clip framebyframe and by reading the time and the position coordinates of the
block off each frame. You will construct a spreadsheet with columns for time and
position and use this spreadsheet to find the velocity as a function of time.
The slope of a velocity versus time graph yields the acceleration of the
block. The force sensor measures the applied force and the mass of the
accelerating object is given in the video clip. Using F_{total }= ma
and F_{total }= F_{applied } f_{k} you will determine
the force of kinetic friction f_{k}. The coefficient of kinetic
friction μ_{k }can then be found from f_{k }= μ_{k}N.
Procedure:
To play the video clip or to step through it framebyframe click the
"Begin" button. The "Video Analysis" web page will open. Choose the friction_3.mp4 and the friction_4.mp4 video clips.
For each video clip:
 Play the video clip and return it to frame 0.
 In the setup window choose to track the xcoordinate of one object.
 Calibrate your data as described in
lab 1.
 Highlight and copy your data table. Open Microsoft Excel, and paste the table into an Excel
spreadsheet.
Your spreadsheet will have two columns,
time (s) and x (m). Produce a graph of position (vertical axis) versus time (horizontal
axis). Label the axes.
 Rightclick the data and choose "Add Trendline". Choose Polynomial, Order 2. and under options click "Display equation on
chart". An equation of the form y = b_{1}x^{2} + b_{2}
x + b_{3} will be displayed where b_{1}, b_{2}, and b_{3}
are numbers.
 For motion with constant acceleration the position
varies with time as x = x_{0} + v_{0}t + (1/2)at^{2}. Since we are plotting x versus t, the number b_{1} is the best
estimate for a/2 from the fit. Therefore the value of the acceleration
determined from the fit is a = 2b_{1}.
 Find the acceleration of the block in each clip.
 Construct a table as shown below. Insert this table
into your log.
surface 
acceleration(m/s^{2}) 
F_{total} (N) 
F_{applied} (N) 
f_{k} (N) 
normal force (N) 
c. of kinetic friction μ_{k} 
wood 






felt 






 Compare the coefficients of static and kinetic friction for
the two surfaces. Comment on your results. Do they make sense?
 How good do you think are your results? What factors do you think may
be responsible for the largest uncertainties?
Experiment 3
Rub your hands together and describe what you feel.
Write down what you think is happening.
Open the Friction simulation.
What do you observe as you rub the two books together? Hit RESET to do
this several times.
Does what you observe in the simulation agree with what your thought was
happening when you rubbed your hands together?
Convert your log into a lab report.
Name:
Email address:
Laboratory 5 Report
 In one or two sentences state the goal of this lab.
 Insert your log with the requested graphs and the answers to the
questions in blue font.
Save your Word document (your name_lab5.docx), go to Canvas, Assignments, Lab
5, and submit your document.