Physics Lab 1.9 Inclined Plane
The
coefficient of friction can be often be easily determined
using an inclined plane. The coefficient of friction is
numerically equal to the tangent of the angle at which
sliding occurs between an object and the surface of the
plane.
This Lab illustrates the construction of a simple
inclined plane apparatus and its use in measuring the
coefficient of friction between pairs of surfaces.
Getting
Started
Set up the equipment illustrated in the video lesson and
carry out the experiments described.
Record the results of the experiment in the table
provided and carry out the calculations needed to
complete the table.
- Why does tapping the
board help us to measure the dynamic friction?
- Calculate the
coefficient of friction for the surface of an
object and the surface of an inclined plane if
the object starts to slide at an angle of 45º to
the horizontal.
- What is the sliding
force acting on a 500 gram block when it is
placed on an inclined plane with an angle of 30º
to the horizontal?
Experiment
1.9.1 Inclined Plane
The purpose of this activity is to construct a simple
inclined plane and use it to measure coefficients of
friction.
Materials and Equipment
- Spring balance –
500 g
- 2 boards, each
roughly 0.5 m x 0.2 m
- 1 board, roughly 0.5
m x 0.5 m
- Duct tape or a hinge
- A wooden block –
mass roughly 300g
- Samples of materials
to be tested.
- A protractor
- Paper
Procedure
- Connect the boards
together as illustrated in the video lesson.
- Weigh the wooden
block and measure the area of the block that will
be in contact with the inclined plane.
- Measure the angle at
which the wooden block slides on the plane –
without tapping the plane. This provides an
indication of the coefficient of static friction.
- Repeat the experiment.
This time tap the board lightly but regularly
while the angle of the plane is being increased.
The block will slide at a much smaller angle.
This indicates the coefficient of dynamic
friction.
- Turn the block on its
side and see whether the area in contact between
the two surfaces has any effect on the
coefficient of friction.
- Now attach different
pairs of materials to the plane and the block and
measure the coefficients of static and dynamic
friction for these combinations.
Calculations
The coefficient of
friction is numerically equal to the tan of the angle of
the plane to the horizontal.
The following is a typical
experimental result:
Results
- Record the results
for each of the pairs of surfaces tested on the
following datasheet:
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Lab 1.8 InclinedPlane |
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Exp
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Description
of surfaces
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Mass
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Angle
1
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Coefficient= |
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Angle
2
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Coefficient= |
#
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in
contact
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of
object
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(Static)
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Tan
of
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(Dynamic)
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Tan
of
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(kg)
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Angle
1
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Angle
2
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- Static friction is slightly larger
than dynamic friction because the sliding object
needs to lift slightly to be able to move over
the irregularities on the surfaces. Tapping the
board allows the moving object to overcome the
initial resistance to movement.
- The coefficient of friction is
equal to the tan of 45º which = 1.00
- From the diagram below, it can be
seen that the sliding force equals the
gravitational force multiplied by the sin of 30º.
The gravitational force = 0.5 kg x 9.81 N/kg = 4.9
N.
The component of this force acting in line with
the surface = 4.9 N x sin 30º.
Sliding force = 2.45 N
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