Physics Laboratory 5

Measuring the coefficients of static and kinetic friction

Objective

In this lab Students 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.

Part I

Find the coefficient of static friction.

Students will examine two video clips, sfriction_1.avi and sfriction_2.avi.  By stepping through these clips frame by frame students 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 block will accelerate.  Using  fs(max)=msN and N=mg, students will determine ms for the wood block and the felt-covered block.

Procedure

To play the video clip or to step through it frame-by-frame click the "Begin" button.  The "Video Analysis" web page will open.  You can toggle between the current page and the "Video Analysis" page by pressing Alt-Tab.  Choose the sfriction_1.avi and the sfriction_2.avi video clips. 

Construct a table as shown below.
surface fs(max) (N) mass (kg) normal force (N) c. of static friction ms
wood        
felt        

Part II

Find the coefficient of kinetic friction.

Students will examine two video clips, friction_3.avi and friction_4.avi.  Students 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.  They 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 students will determine the force of kinetic friction fk.  The coefficient of kinetic friction mk can then be found from fk = mkN.

Procedure

To play the video clip or to step through it frame-by-frame click the "Begin" button.  The "Video Analysis" web page will open.  You can toggle between the current page and the "Video Analysis" page by pressing Alt-Tab.  Choose the friction_3.avi and the friction_4.avi video clips. 

Find the acceleration of the block in each clip by following the procedure described in Lab 4.
Construct a table as shown below.
surface acceleration (m/s2) Ftotal (N) Fapplied (N) fk (N) normal force (N) c. of kinetic friction mk
wood            
felt            

Open Microsoft Word and prepare a report using the template shown below.

Name:
E-mail address:

Laboratory 5 Report

In a few sentences summarize the experiment.

Insert your tables.

Compare the coefficients of static and kinetic friction for the two surfaces.  Comment on your results.

How good do you think are your results?  What factors do you think may be responsible for the largest uncertainties?

Save your Word document (your name_lab5.doc) and attach it to an e-mail message to mbreinig@utk.edu.