PASCO ME-6950 PAScar with Mass - Manual (Page 21)

012-07361B PAScar with Mass
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Figure 6.2
Procedure
NOTE: To get consistent results in this experiment, you must insure that the ramp you will be
using is both straight and clean. Wipe the surface of the ramp and the friction block with a rag.
Determining coefficient of kinetic or “sliding” friction:
1. Place the car with the friction block on the ramp. Set up the ramp at a relatively low angle (one that
does not cause the friction block to begin sliding down the ramp by itself).
2. Increase the angle of the ramp until the block begins to slide down the ramp on its own, but only after
you “release” it by slapping the table (or tapping the ramp very lightly). Now increase the angle of the
ramp by a few more degrees, so that the block will slide down the ramp with a uniform acceleration
when you release it with a “slap” or tap. The angle of the ramp must be low enough so that the block
does not begin to slide on its own - only when you release it. Measure the angle of the ramp with the
protractor and record it as the angle of uniform acceleration (ø) in the data table.
3. Release the block from the grasp of static friction as
described in the previous step and measure the time
of the car’s descent down the ramp. Record this time
as t in data Table 6.1. Measure the distance d that the
block slides down the ramp and record this data in
Table 6.1. Repeat the measurements four times. Use
EQN-3 to compute the accelerations of the block and
enter the values in data Table 6.1. Determine the
average value of acceleration and enter it below data
Table 6.1.
4. Use EQN-2 to calculate the coefficient of kinetic or
“sliding” friction. Enter it below the data table.
Prediction of D and Measurement of D:
5. Now slightly reduce the angle of the ramp until the block will just barely slide down the ramp with a
uniform speed when you release it with a slap or tap. Measure this “slip” angle. Reduce the angle of the
ramp to about one half of the “slip” angle. Measure this new angle and record its value in data Table
6.2 as
θ. Secure a brick or block at the upper end of the ramp as shown in Figure 6.2.
6. It is time to make a prediction – Using EQN-1 and the information that you have recorded, predict D,
the distance that the car will slide down the ramp after being launched. Assume that the plunger on the
car is fully cocked at the position of maximum spring compression. Record your prediction at the top
of Table 6.2.
7. After double checking your work in the previous step, launch the car down the ramp by placing it on
the ramp with its cocked plunger against the secured brick. Then tap the spring-release trigger with a
rod or stick using a flat edge.
NOTE: This will help to insure that you do not give the car an initial velocity other than that
supplied by the spring plunger.
8. For six trials, measure the distance D that the car slides and record these in Table 6.2.
NOTE: Sometimes the car will twist a bit as it descends, so use the midpoint of the back edge of
your car as a reference point for measuring D.
9. Compare your results with your prediction. Compute the percent difference between these two values
and enter it below Table 6.2.
Block or
brick
(about 1/2 the
slip angle) θ