Download Static Friction

NAME: __________________________________________
PERIOD: ________
Lab 2B-2: Static and Kinetic Friction
OBJECTIVES

Use a Dual-Range Force Sensor to measure the force of static friction.
 Determine the relationship between force of static friction/kinetic friction and the
weight/Normal Force of an object.
MATERIALS
computer
Vernier computer interface
Logger Pro
Vernier Force Sensor
string
carts with different surfaces
balance or scale
mass set
Mass
Wooden block
Dual-Range
Force Sensor
Pull
PROCEDURE
1. Choose a cart, and measure its mass use the balance at the front of the classroom. Circle the
cart used, and record the mass in the data table.
2. Connect the Dual-Range Force Sensor to Channel 1 of the interface. Set the range switch on
the Force Sensor to 50 N.
3. Open the file “12a Static Kinetic Frict” from the drop box.
4. Tie one end of a string to the hook on the Force Sensor and the other end to the hook on the
wooden block. Place a total of 1 kg mass inside the cart, fastened so the masses cannot shift.
Practice pulling the block and masses with the Force Sensor using this straight-line motion:
Slowly and gently pull horizontally with a small force. Very gradually, taking one full second,
increase the force until the block starts to slide, and then keep the block moving at a constant
speed for another second.
5. Hold the Force Sensor in position, ready to pull the block, but with no tension in the string.
Click
to set the Force Sensor to zero.
6. Click
to begin collecting data. Pull the block as before, taking care to increase the
force gradually. Repeat the process as needed until you have a graph that reflects the desired
motion, including pulling the block at constant speed once it begins moving.
7.
8.
Now you will measure the peak static friction force and the kinetic friction force as a
function of the normal force on the block. In each run, you will pull the block as before, but
by changing the masses on the block, you will vary the normal force on the block.
To find the value of the static friction off the force vs. time graph, examine the data by
clicking the Statistics button, . The maximum value of the force occurs when the block
started to slide (creating a peak on the graph). Read this value of the maximum force of static
friction from the floating box and record the number in your data table.
Physics with Vernier
12 - 1
Lab 2B-2
9. To find the value of the kinetic friction, highlight the segment of the graph that leveled out
(when the cart was moving at a constant velocity). Click the statistics button again to read
the mean or average force during this portion. This represents the magnitude of the kinetic
frictional force.
10. Repeat Steps 6-9 for two more measurements and average the results to determine the
reliability of your measurements. Record the values in the data table.
11. Repeat Steps 6-10 with 4 more weights, recording values in the data table.
DATA TABLE
Type of Cart Used
Cork
Plastic
Mass of Cart
Felt
kg
Table 1. Peak Static Friction
Peak static friction
Total mass
(m)
Normal
force
(N)
Trial 1
Trial 2
Average
Trial 3
peak static
friction
(N)
Table 2. Kinetic Friction
Kinetic friction
Total mass
(m)
12 - 2
Normal
force
(N)
Trial 1
Trial 2
Trial 3
Average
kinetic
friction
(N)
Physics with Vernier
Static and Kinetic Friction
ANALYSIS
1. Plot a graph of the maximum static friction force vs. the normal force on Logger Pro. Write
the equation of the line below.
2. Create a plot of the average kinetic friction forces vs. the normal force (you can add a new
page if you want). Write the equation of the line below.
3. What is the relationship between static friction and the normal force? And between kinetic
friction and the normal force?
4.
Compare the slopes of the two equations and explain the differences. What do you think the
slopes represent?
5. Is there a significant intercept? Why or why not?
6. Discuss your possible sources of error.
Physics with Vernier
12 - 3