PASCO ME-9430, Instruction Manual And Experiment Manual

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012-04840E
Dynamics Cart
20
®
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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 cart 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 will begin 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 cart’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 in data 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 reduce the angle of the ramp slightly 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 cart will slide down the ramp after being launched. Assume that the plunger
on the cart 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 cart 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 cart an initial velocity other than that
supplied by the spring plunger.
8. For six trials, measure the distance
D
that the cart slides and record these in Table 6.2.
NOTE:
Sometimes the cart will twist a bit as it descends, so use the midpoint of the back edge of
your cart 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.
Figure 6.2
Block or brick
(about 1/2 the slip angle)