Download 10 Friction File

Student _______________________________________
Lab # _____
Lab Date ________________
Due Date ________________
Static & Kinetic Friction
PURPOSE: (1) To determine the effect that an increase in mass has on the force of friction.
(2) To determine the coefficient of static friction and kinetic friction for wood on
four different surfaces.
MATERIALS: wooden block; different surfaces; force sensor; GLX Xplorer; masses
INTRODUCTION:
Friction is a very common and sometimes troublesome force that is a result of two surfaces in
contact with each other. Friction is a force that opposes the motion of an object. If the object is
at rest, the force of friction opposing the start of motion is called static friction. If the object is
moving, the force of friction that opposes the motion is called
kinetic friction. Static friction is less than kinetic friction which
means that a smaller force is needed to maintain motion. The
force sensor is easy to zero just press the button and the zero
setting is stored digitally. No confusing manipulations of data
are necessary. Make sure you place the force sensor parallel to
the plane of the board and use the digit display to measure the
forces in the direction of the sensor.
PRE-LAB: Answer all questions in complete sentences.
1. Draw a free body diagram showing a wooden block with a
force being applied to the right. Show the direction of the gravitational force (weight), normal
force and frictional force acting on the object.
2. How does the maximum force of static friction compare to the force being applied for an object
that is just about to move? ________________________________________________________________________________
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3. How does the force of kinetic friction compare to te force being applied for an object moving
with constant speed? ______________________________________________________________________________________
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4. How does the gravitational force (weight) compare to the normal force? _________________________
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PROCEDURE & DATA:
Lay the wooden block on one surface. The weight of wooden block is 25 g, which is
approximately 0.25 N. Change the mass on top of the block 5 times. Pull on the force sensor with
two fingers and practice sliding the block across the surface at constant speed. Record with the
GLX Xplorer the force needed to just above move the block (the maximum static friction force)
and the force needed to keep the block moving at a constant speed (the kinetic friction force).
CARDBOARD
Weight
Fg (N)
Normal Force
FN (N)
Max Static Friction
Force Ffsmax (N)
Kinetic Friction
Force Ffk (N)
s
k
s
k
s
k
s
k
2.25
3.25
4.25
5.25
6.25
Average
CORK
Weight
Fg (N)
Normal Force
FN (N)
Max Static Friction
Force Ffsmax (N)
Kinetic Friction
Force Ffk (N)
2.25
3.25
4.25
5.25
6.25
Average
RUBBER
Weight
Fg (N)
Normal Force
FN (N)
Max Static Friction
Force Ffsmax (N)
Kinetic Friction
Force Ffk (N)
2.25
3.25
4.25
5.25
6.25
Average
SANDPAPER
Weight
Fg (N)
Normal Force
FN (N)
Max Static Friction
Force Ffsmax (N)
Kinetic Friction
Force Ffk (N)
2.25
3.25
4.25
5.25
6.25
Average
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CONCLUSIONS:
1. Does the dragging speed have any effect on the coefficient of sliding friction?
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2. At each weight, how does the static force compare with the sliding force?
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3. If you press down on the block while it is sliding, the force of friction increases but the
coefficient does not. Explain why.
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4. Why are there no units for the coefficient of friction?
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5. What is the physical significance the slope of Ff vs. FN?
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6. A force of 450 N is used to pull a desk weighing 700. N across the classroom floor at a
constant velocity.
a. What is the frictional force on the desk? [Show all calculations, including equation
and substitution with units.]
b. What is the coefficient of kinetic friction? [Show all calculations, including
equation and substitution with units.]
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