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 felt-covered 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.
Find the coefficient of static friction.
You will examine two video clips. By stepping through these clips frame by frame
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 fs(max) = μsN
and N = mg,
you will determine μs for the wood block and the felt-covered block.
To step through video clips frame-by-frame click the
buttons below. The "Video Analysis" web page
Construct a table as shown below. Insert this table
into your log.
||normal force (N)
||c. of static friction μs
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 frame-by-frame 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 Ftotal = ma
and Ftotal = Fapplied - fk you will determine
the force of kinetic friction fk. The coefficient of kinetic
friction μk can then be found from fk = μkN.
To play the video clip or to step through it frame-by-frame 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 x-coordinate of one object.
- Calibrate your data as described in
- Highlight and copy your data table. Open Microsoft Excel, and paste the table into an Excel
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.
- Right-click the data and choose "Add Trendline". Choose Polynomial, Order 2. and under options click "Display equation on
chart". An equation of the form y = b1x2 + b2
x + b3 will be displayed where b1, b2, and b3
- For motion with constant acceleration the position
varies with time as x = x0 + v0t + (1/2)at2. Since we are plotting x versus t, the number b1 is the best
estimate for a/2 from the fit. Therefore the value of the acceleration
determined from the fit is a = 2b1.
- Find the acceleration of the block in each clip.
- Construct a table as shown below. Insert this table
into your log.
||normal force (N)
||c. of kinetic friction μk
- 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?
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.
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.