332 PHYSICS
FRICTION LAB
PURPOSE: TO DETERMINE THE COEFFICIENT OF STATIC AND KINETIC FRICTION for various surfaces.
MATERIALS: LABQUEST, 20cm string, FRICTION BOXES, FORCE SENSOR BOX, WOODEN PLANK, MASSES.
PROCEDURE:
1) PLACE plank on lab table. Obtain friction box that has CORK on bottom.
2) Set force sensor to ±10N setting. Turn on LabQuest device. Plug force sensor into CH 1.
3) With force sensor lying on table (nothing attached to hook), using the stylus, tap SENSORS → tap ZERO.
4) Tie one end of string to friction box. Tie other end to force sensor hook.
5) Position force sensor and friction box on plank as shown at right.
6) Make sure the string is PARALLEL TO PLANK.
7) Place 300g into box.
8) PRACTICE THIS: Using stylus, tap collect button (lower left arrow). With the
string a little slack, SLOWLY and gradually, increase the force until the box starts
to slide, and then keep the block moving at a constant speed for another second.
If you are successful, your graph will resemble the one at right.
9) Prepare to pull like in step 8. Using stylus, tap collect button. Once you have
achieved this, tap STOP BUTTON.
10) Using stylus, HIGHLIGHT the area around the peak of graph as shown below.
Tap ANALYZE → STATISTICS → check FORCE BOX. Statistics should show on right
of screen.
11) Record the MAX VALUE. This is the maximum static
friction occurring at the peak of graph, right before box
broke free.
12) Tap ANALYZE → STATISTICS → uncheck force box.
Highlight should disappear.
13) Highlight the flat section ONLY (after peak). Repeat
step 10. RECORD MEAN VALUE. This represents the
kinetic friction when box was sliding.
14) Repeat steps 9-13 adding 300g at a time until you have completed 6 total trials (up to and including 1800g).
15) REPLACE cork friction box for a FELT friction box FOR PART 2. Repeat lab.
16) RECORD mass of BOTH empty friction boxes.
ANALYSIS:
1) For the Data Section, see back side for examples.
2) For the Calculations Section:
For Part I and II, calculate the normal force on the box for each combination of added masses.
Show how you determined this. Only 1 example calculation is necessary. Place the values to
the normal force in a table similar to one shown for each surface.
Cork Surface
Total
mass
(including
block)
(kg)
Normal force
(N)
3) For the Graph Section:
a. Plot a graph of the maximum static friction force (vertical axis) vs. the normal force
(horizontal axis) for CORK. On the same graph, plot static friction values for FELT. Use
different point protectors to distinguish. Insert best-fit lines for both and have Excel
determine slope. Place slope on graph for each line. Determine what the slope represents
and place in your summary.
b. Plot a graph of the kinetic friction force (vertical axis) vs. the normal force (horizontal axis)
for CORK. On the same graph, plot kinetic friction values for FELT. Use different point
protectors to distinguish. Insert best-fit lines for both and have Excel determine slope.
Place slope on graph for each line. Determine what the slope represents and place in your
summary.
4) For the Conclusion Section:
Thoughts for discussion (do not list these questions, rather, work them into conclusion): What
are your graphs telling you between static and kinetic? What are the graphs telling you about felt
vs cork? Does the force of kinetic friction depend on the weight of the block? Explain. Does the
coefficient of kinetic friction depend on the weight of the block? Explain. Why was it important
to pull the block at constant speed for kinetic friction? Explain.
SAMPLE DATA TABLES FOR FRICTION LAB
Mass of box
kg
Part I: Max Static Friction and Kinetic Friction
Cork surface:
STATIC FRICTION VALUE
Total
mass
(including
block)
(kg)
KINETIC FRICTION VALUE
Maximum
static
friction
(N)
Total
mass
(kg)
MEAN kinetic
friction
(N)
Part 2: Max Static Friction and Kinetic Friction
FELT surface: STATIC FRICTION VALUE
Total
mass
(including
block)
(kg)
Maximum
static
friction
(N)
KINETIC FRICTION VALUE
Total
mass
(kg)
MEAN kinetic
friction
(N)