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LAB
FACTORS AFFECTING FRICTION
Mr. Koenig
Factors affecting friction.
Concepts to Investigate: Friction equation, coefficient of static friction, coefficient of sliding
friction (kinetic), independence of surface area and friction.
FN
Ffriction
Fapplied
m1
m1
m1g = Wt
Friction is the force that opposes
motion
The minimum force needed to keep a
body moving is equal to the friction
force.
That is, Fapplied = Ffriction, if velocity  0
& Acceleration = 0
Weight (Wt) is the downward force
of gravity. If no other forces act on
the object then Wt = FN, where FN is
the upward force the surface exerts
on the object.
Materials Needed:
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Athletic shoe
Set of masses
Pasco force sensor
Computer with Data Studio
Koenig Physics 2014-15
Direction of motion (constant velocity)
Fk and Fs
Fapplied
Force probe
Computer w/ Data
Data Studio
Shoe
USB
link
Procedure:
To Open Data studio: plug USB connector into computer and a force probe to the USB link.
Each time the Force probe is to be used you must click the start key on the computer and then the zero button on the Force probe,
then you may use the probe to pull, push, or hang something.
In order to calculate the weight of the friction shoe, first click the start key on the computer and then click the zero
button on the force probe then hang the friction Shoe from it and hold as steady as possible.
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Attach a force probe to the Shoe. Press the start button on the computer to prepare it for data collection.
While in the relaxed position, press the zero button, on the force probe- Pull horizontally until the Shoe
JUST begins to move. Measure this value as the magnitude of static friction, (the force required to set the
shoe sliding) Remember, pull gently and watch for when the Shoe just “Breaks Free”, record the force
required to accomplish this. When the shoe has no additional mass in it you may have to do this several
times to get an accurate average value. Use the digits display with the graph display.
After the shoe begins to move measure the force required to keep it moving at a constant velocity.
This is a measurement of the magnitude of the sliding friction force (kinetic).
Repeat these procedures by completing the table below.
Graph your results, using the weight of the shoe as the independent variable (x-axis), and force of friction
as the dependent variable (y-axis). Using Graphical Analysis plot the Friction vs. Normal Force (weight)
and determine the relationship.( i.e: determine the slope of the line) for both Static and Kinetic friction.
Graph both static values and kinetic values on the same graph.
What can you conclude from your results concerning the relationship of weight and friction?
Shoe #1 on Surface #1
Part 1
Does wt. Affect
Friction?
Shoe
Shoe+ 100g
Shoe +200g
Shoe+300g
Shoe+400g
Shoe +500g
Shoe +600g
Shoe +700g
Shoe + 800g
Shoe + 900g
Shoe + 1kg
Koenig Physics 2014-15
Weight
(N)
Static
friction
(N)
Sliding
friction
(N)
Shoe #1 Surface #2
Part 1
Does wt. Affect
Friction?
Weight
(N)
Static
friction
(N)
Sliding
friction
(N)
Shoe
Shoe+ 100g
Shoe +200g
Shoe+300g
Shoe+400g
Shoe +500g
Shoe +600g
Shoe +700g
Shoe + 800g
Shoe + 900g
Shoe + 1kg
The friction equation states Ff =  FN where Ff is the force of friction, and FN is the normal force. This is the
equation of a straight line with the slope equal to the coefficient of friction . (y=mx+b)
Thus, a graph of friction as a function of weight should produce a straight line with a slope equal to the coefficient
of friction.
1) Does a graph of your data produce a straight line?
2) Determine the coefficient of friction by measuring the slope.
3) Inspect your results in the table and describe the relationship between weight and static friction, and
between weight and kinetic (sliding) friction
4) Will the soles of your shoes wear out faster when hiking or back- packing with a pack on your back?
Explain.
5) Do you think the coefficient of friction is different for each surface the shoe is in contact with?
Give reasons for your answer.
6) Do you think the surface area of contact affects friction? Explain.
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Answer all questions to this lab.
1 lab for each person(no more than 4 persons per group)
All answers to questions to be typed.
Graph should show all calculations (if printing is unavailable graph paper will be used)
Attach the data table to your graph.
Be sure to include names of all lab partners on the report.
Koenig Physics 2014-15
Koenig Physics 2014-15