In this experiment, students will use a Motion Sensor to discover
the relationship between the force of sliding friction and the
working on a sliding object. Using this relationship, they will
be able to solve for the coefficient of kinetic friction.
Click the Start button and then release the car's
plunger. Data collection will automatically stop after 3
seconds.
Reset the car and record one more data run.
Now, remove the cork-bottomed tray and place it in front
of the car, so the car will push it down the track when
the plunger is released.
Push the plunger into the second setting and place the
car against the metal flap on the Force Accessory bracket.
Click the Start button and then release the car's plunger.
Record the change in position of the tray/car system resulting
from the force exerted on it.
Reset the car and record one more data run. Note the change
in position for this data run as well.
Describe the changes in energy as the car is
released with the cork-bottomed tray riding in the car.
Describe the changes in energy as the car is released
and pushes the cork-bottomed tray down the track.
How is the motion of the tray/car system different for
the situations described in questions 1 and 2? Explain why
the motion is different.
Use the mass of the tray/car system and the maximum velocity
to find its kinetic energy. Use data when the tray is riding
in the car for this calculation.
Use this kinetic energy and the change in position you
measured to determine the force of kinetic friction between
the track and cork-bottomed tray (Hint: W = Fx).
Use the force of kinetic friction and the normal force
of the tray/car system to find the coefficient of kinetic
friction.
Compare your answer to the table of friction coefficients
in your textbook to see if your answer is reasonable. Explain
why or why not.
If this experiment was repeated with the plastic-bottomed
tray, how would the results change? Explain the rationale
behind your answer.
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