PASCO ME-8930 SMART TIMER - Manual (Page 22)

Smart Timer 012–06734A
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5. Place the Dynamics Cart on the track, attach a string to the hole in the end of the cart,
and tie a mass hanger on the other end of the string. The string must be just long enough
so the cart hits the end stop before the mass hanger reaches the floor.
6. Pull the cart back until the mass hanger reaches the pulley. Make a test run to determine
how much mass is required on the mass hanger so that the cart takes about 2 seconds to
complete the run. Record the hanging mass in Table 2.1.
7. Set up the Smart Timer to record Acceleration: Linear Pulley.
Note: Use masses of between 50 and 100 g, and be sure that the runs are not
longer than 2 seconds.
8. Pull the cart back until the mass hanger reaches the pulley. Release the cart from rest,
and activate the Smart Timer once the car has started moving. (The timing will begin
when the photogate beam is first blocked.) Repeat this measurement 3 times with the
same masses. Record all the values in Table 2.1. Calculate the average accelerations and
record in Table 2.1.
9. Increase the mass of the cart using the bar mass and repeat the procedure.
Analysis
1. Calculate the measured force F = (m
1
+ m
2
)a and record in Table 2.1.
2. Calculate the theoretical force F = m
2
g and record on Table 2.1.
3. Calculate the percent difference of the theoretical force vs. the measured force and
record in Table 2.1.
Questions
1. Did the results of this experiment verify that F = ma? Explain.
2. Why is the mass in F = ma not just equal to the mass of the cart?
3. When calculating the force on the cart using mass times gravity, why isn’t the mass of
cart included?
4. Discuss the impact on the results of assuming the frictional force to be zero.
* % difference =
theoretical – measured
theoretical
x 100%
cart hanging ave. measured theoretical
mass (m
1
) mass (m
2
) accel. 1 accel. 2 accel. 3 accel. force force % difference*
a (m
1
+ m
2
)a m
2
g
Table 2.1 Data