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Experiment
Pendulum and the Calculation of g
Experiment
Pendulum and the Calculation of g
Lab 6 Simple Pendulum
Discussion and review
A simple pendulum consists of a mass (“bob”) suspended from a light string of length
L. The bob is pulled sideways such as the string makes with the vertical direction an angle θ less than 150. When is released it oscillates back and forth within a vertical plane, with the period of the pendulum given by: T = 2π
symbol 
Description 

Period of a pendulum to complete one cycle 

Length of string 

Acceleration due to gravity: 9.81 m/s2 
Procedure
The lab activity uses a simulation developed by the University of Colorado at Colorado Boulder. Click on the link below and choose “Intro”.
1. The length of the pendulum should be set to the following lengths: 0.25, 0.5, 0.75 and 1m.
2. For each length, set the pendulum in motion by displacing the pendulum bob sideways such as the string makes
100 with the vertical direction
.
3. Start the timer when the strings appear to be aligned with the angle. Wait for next alignment and count first oscillation, the next alignment will be the second oscillation and so on. Count out a total of 10 oscillations and stop the timer precisely on the 10th oscillation. Record the total time elapsed for the 10 oscillations.
4. Repeat the previous step a total of 3 times and calculate the average of the three time trials
Tavg
5. Calculate the oscillation period,
T
, by dividing the average time by ten.
6. Calculate the acceleration due to gravity,
g
, for all lengths of the pendulum, using
T2
and the equation:
Length (m) 
Time [Trial 1] (s) 
Time [Trial 2] (s) 
Time [Trial 3] (s) 
Timeavg (s) 
T = Timeavg/10 (s) 
T2 (s2) 
g(m/s2) 
gavg(m/s2) 
1.00 m 

0.75 m 

0.50 m 

0.25 m 
Analysis
1. How is the period of the pendulum changing with length?
2. Why did you measure 10 periods of the pendulum instead of just 1?
3. What do you think the effect of the changing mass will be on the pendulum’s period if the length is fixed? Why?
You can check your assumption by running the simulation. Keep the angle to less than 150.
4. Calculate your percentage error as compared to the accepted value for
g, which is 9.81 m/s2.
% error = [
experimental value – accepted value] × 100
accepted value
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