Download Friction Lab (Anything written in Italic Font should be deleted when

Friction Lab
(Anything written in Italic Font should be deleted when you turn in your lab)
Grading Rubric
Section
Paper - Table
& Graph
Sandpaper Table & Graph
Vinyl Wood Concl. #1 Concl.#2
Table &
Table &
Graph
Graph
Points
5 pts
5 pts
5 pts
5 pts
10 pts
10 pts
Purpose – To determine the coefficient of static friction for several different surfaces.
Concl#3
10 pts
Prediction – Before beginning, predict the order of surfaces from lowest to highest coefficients of static
friction below. The four surfaces are: Paper, Sandpaper, Vinyl and Wood.
Lowest µs
-____ -____ -____ -____ Highest µs.
Background
The force of friction between an object and a surface is dependent upon the makeup of the object & surface,
the mass of the object, and whether or not the object is moving. The force of friction present for a stationary
object is known as static friction. After enough force is applied to the object to overcome this static friction
force (seen in the Force (N) vs. time (s) graph below as the “Breakaway” point), the object begins to move and
now the force of fiction present is known as kinetic friction.
The force of friction can be calculating using the formula FF = µ·FN where FF is the force of friction, µ is the
coefficient of friction between the object and the surface, and FN is the normal force the surface exerts on the
object. The normal force of an object on a flat surface is equal to the weight of the object, and can be
calculated by multiplying mass of the object in kilograms by the acceleration due to gravity (9.8 m/s2) FN = mg.
A graph of static friction force plotted on the y-axis
versus a graph of normal force plotted on the x-axis,
can be used to calculate the coefficient of friction
between an object and a surface, by calculating the
slope of the line. The sample graph to the right shows a
calculated coefficient of friction of 0.2781.
Materials
- Friction Block
o (w/pole m = 81.4 g. w/out pole m = 78.6g)
- Five – 100 gram washers
- Dual Range Force Sensor – (DRFS)
- Computer with Logger Pro
- Lab Quest or Lab Quest Mini
-Meter stick
Procedure Setup
Connect the Dual Range Force Sensor to the computer by plugging the sensor into channel 1 (CH1) of the Lab
Quest / Mini. Using the computer, open Logger Pro. Be sure the DRFS is recognized by the program. The
screen should have a graph of Force (N) vs. time (s) and a clickable, green “Collect” button. Place the friction
block on the meter stick. Hook the DRFS onto the hook of the friction block.
Collecting Data
After clicking on the green “Collect” button, use the DRFS to pull the friction block so that it moves from rest
WITH THE LEAST AMOUNT OF FORCE POSSIBLE. After allowing the block to come to rest, again pull on the
friction block with the DRFS so that it moves with the least amount of force possible. Repeat for at least three
trials. To better view the graph, click on the “Autoscale Graph” icon at the top of the screen.
In order to measure the force, click on the “Examine” icon located at the top of the screen.
Move the cursor along the line of the graph so that it reads the peak of the static friction force
generated to move the block.
Select and measure the peaks of the other trials (highlighted below) and average together the
measurements of a single average force of friction. Record the average as the force of static
friction in the data table(s).
Add one additional washer to the top of the friction block to increase the normal force, and repeat the process
for measuring and averaging the force of static friction. Continue adding an additional washer and measuring
force of static friction until all 5 washers are used.
Rotate the friction block so that a different surface of the block is resting on the meter stick. Repeat the
process for each surface, averaging at least three force measurements for each surface, and adding one
additional washer until all 5 washers are used for each of the four surfaces.
Analyzing Data
For each surface, create a graph (in excel) of Force of Static Friction (FF) vs. Normal Force (FN). Check back in
the Background for information to calculate the normal force. Find the slope of the graph and record as the
coefficient of static friction.
Data
Surface: Paper_
Normal
Force – N
(FN)
Block
0.79772*
(w/pole)
Block + 1
Washer
Block + 2
Washers
Block + 3
Washers
Block + 4
Washers
Block + 5
Washers
Surface: Sandpaper_
Normal
Force – N
(FN)
Block
Block + 1
Washer
Block + 2
Washers
Block + 3
Washers
Block + 4
Washers
Block + 5
Washers
Avg. Force of
Static Friction
- N (FF)
Insert Graph Here
Coefficient of static friction µs. : __
Avg. Force of
Static
Friction - N
(FF)
Insert Graph Here
0.79772*
(w/pole)
Coefficient of static friction µs. : __
Surface: Vinyl_
Normal
Force – N
(FN)
Block
Avg. Force of
Static
Friction - N
(FF)
0.79772*
(w/pole)
Block + 1
Washer
Block + 2
Washers
Block + 3
Washers
Block + 4
Washers
Block + 5
Washers
Coefficient of static friction µs. : __
Surface: Wood_
Normal
Force – N
(FN)
Block
Block + 1
Washer
Block + 2
Washer
Block + 3
Washer
Block + 4
Washer
Block + 5
Washer
Insert Graph Here
Avg. Force of
Static
Friction - N
(FF)
Insert Graph Here
0.79772*
(w/pole)
Coefficient of static friction µs. : __
Conclusion
1. Using your calculated values for each surfaces’ coefficient of friction, order them from least to greatest.
Lowest µs
-____ -____ -____ -____ Highest µs.
Compare these results to your predictions and explain any possible differences.
2. Explain why finding the slope of a graph of Static Friction Force vs. Normal Force is used to calculate the
coefficient of friction.
3. Explain how adding washers to the friction block changes the force of static friction required to move the
block from rest.