PASCO ME-8950A COMPLETE ROTATIONAL SYSTEM - Manual (Page 25)

012-05293F Complete Rotational System
21
5. Calculate the centripetal force from the slope
and record in Table 3.2.
6. Calculate the percent difference between the
two values found for the centripetal force
and record in Table 3.2.
Part II: Vary Force (constant radius and mass)
The radius of rotation and the mass of the hanging object will be held constant for this part of the
experiment.
1. Weigh the object and record its mass in Table 3.3. Hang the object from the side post and connect
the string from the spring to the object. The string must pass under the pulley on the center post.
2. Attach the clamp-on pulley to the end of the track nearer to the hanging object. Attach a string to
the hanging object and hang a known mass over the clamp-on pulley. Record this mass in Table
3.3. This determines the centripetal force.
3. Select a radius by aligning the line on the side post with any desired position on the measuring
tape. While pressing down on the side post to assure that it is vertical, tighten the thumb screw on
the side post to secure its position. Record this radius in Table 3.3.
4. The object on the side bracket must hang vertically: On the center post, adjust the spring bracket
vertically until the string from which the object hangs on the side post is aligned with the vertical
line on the side post.
5. Align the indicator bracket on the center post with the orange indicator.
6. Remove the mass that is hanging over the pulley and remove the pulley.
7. Rotate the apparatus, increasing the speed until the orange indicator is centered in the indicator
bracket on the center post. This indicates that the string supporting the hanging object is once
again vertical and thus the hanging object is at the desired radius.
8. Maintaining this speed, use a stopwatch to time ten revolutions. Divide the time by ten and record
the period in Table 3.3.
9. To vary the centripetal force, clamp the pulley to the track again and hang a different mass over
the pulley. Keep the radius constant and repeat the procedure from Step #4. Do this for a total of
five different forces.
Analysis
1. The weight of the mass hanging over the pulley is equal to the centripetal force applied by the
spring. Calculate this force for each trial by multiplying the mass hung over the pulley by “g” and
record the results in Table 3.3.
2. Calculate the inverse of the square of the period for each trial and record this in Table 3.3.
3. Plot the centripetal force versus the inverse square of the period. This will give a straight line
since:
4. Draw the best-fit line through the data points and measure the slope of the line. Record the slope
in Table 3.3.
F
4 π
2
mr
T
2
---------------- =
Centripetal Force = mg
Centripetal Force From Slope
Percent Difference
Table 3.2: Results (varying raduis)