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THE PENDULUM LAB

Completed February 15, 2010 

By Natalia A.E. and Cat D.


 Purpose

The purpose of this lab was to discover the variables that affect the period length (the time it takes for a bob to swing forth and then return to its starting place once) of a pendulum the greatest. The tested variables were: the angle of release, the mass of the bob, and the length of the string.

  1. Hypothesis

    We expect the variable that will cause the greatest effect on the pendulum's period length the most is the angle of release--a greater angle resulting in a faster time, and a lesser angle resulting in a slower time. 



Materials

As shown in the image above, the materials included:
  • 3 bobs with masses of: 100 grams, 500 g, and 1000 g
  • String to suspend the bob (39 cm is shown; we also tested a 10 cm string)
  • Protractor to determine angle of release

Procedure

1. The apparatus was assembled.

2. The 100 g bob was suspended on the 39 cm string. Using the protractor, the bob was released at an angle of 20 degrees. The length the bob took to complete 10 periods was recorded.

3. For each variable, 3 trials of data were recorded.

The process in number 2 was repeated; changing the masses of the bob to 500 g and 1000 g; then the 100 g bob was returned to the string and the angle of release was changed to 10 degrees and 30 degrees, and the length of string to 10 cm  instead of 39 cm.

4. The necessary calculations were performed to determine the average length of one period for each variable and  the results were studied to determine which variable yielded the greatest change in average period time.

After these steps, the data collection was complete.

Data











Analysis

This experiment proved that the length of the string effects the period length of the swing of a pendulum the most. This data was compared to other variables, which included angle of release and mass of the bob. The starting length, 39 centimeters, demonstrated a much slower period time then the smaller length, 10 centimeters. On average, the difference in time of the period for the string lengths was 0.494 seconds. The average difference of time for the various masses was 0.073 seconds and the average difference of time for the various angles of release was 0.004 seconds. Evidently, the difference in time for the length of string is the greatest difference compared to the other variables. Therefore, our hypothesis was not supported. The outcome of the difference for angle of release actually proved to be the smallest difference compared to the other variables.

We conclude that the length of string effected the time of the period swing the most because with the longer string the bob had much more distance it could cover, when with the shorter length it could only swing a short distance. Since the longer length string had more distance to cover, it took a greater amount of time to reach its release point. The shorter length string did not have much distance to cover, making it return to the release point in a shorter amount of time. 

Sources of Experimental Error

The sources of experimental error on this particular lab are found in measurement of the period, angle, and length of the string. Since there is no exact stopping point for the period of the swing, it is difficult to stop the stopwatch at the exact same point of the string multiple times. It is also difficult to synchronize the moment when the stopwatch person says "Go" while pressing the start button with the instant the partner releases the pendulum bob. Also, the protractor was held at a difficult place to determine the exact angle while collecting data, the angles of release could not be exact. In addition, because we had to create the same exact length of the string on two separate days, the exact length of the string varied slightly. Naturally, these potential errors prevented the ability to obtain exact, precise data.

Summary

This experiment tested what variable would effect the length of a period of a pendulum swing the greatest. Our hypothesis suggested that the angle of release of the bob would create the greatest effect on the length of a period. Our trials, however, proved that the length of string made the greatest effect on the period. This was proven by testing each of the variables in three trials. 


Comments

Rita G - Feb 16, 2010 2:23 PM

Your analysis goes well in-depth, as do your sources of error and your summary. Your data is easy to understand and to read. It also seems to have been collected well, with the exception of the length vs. time data. Instead of three different lengths, only two were used, making it slightly incomplete. Your analysis is highly detailed and the data is explained very well. This report is very good, even if it all the data is not entirely complete.
R. Grosbard

Jane Rem - Feb 16, 2010 3:43 PM

Your website is very organized and looks great! I really like the theme you chose and the way you put the text and picture side by side. However, the graphs are a bit small and hard to read. By making both the charts and graphs bigger, they would fill up the column and there would be less empty space in your project. Other than that, your analysis and summary are easy to follow and explain your point very well. Overall, I think you demonstrate an understanding on the subject in a very aesthetically pleasing format.
-JaneR

christina mccarthy - Feb 16, 2010 4:31 PM

Your website is well structured, and pleasing to look at to the eye. Although, at first it is slightly confusing to determine which data table goes with which graph. Breaking the data up into sections with lines, as you did with the rest of the site, may be helpful to the viewer. Your analysis and experimental error are very in-depth and well thought out. Credits to you two for making a great website.

Kevin Mahaffey - Feb 18, 2010 8:12 PM

I like the format and coloring of this page. The analysis is probably the strongest part of this site and because it is very detailed and the summary is straight forward. Some weaker parts include the material list which could be bigger and the graphs were kind of small. Other than that great job!