206Conclusion Sample-2004   206ConSam

Sample conclusion for a pendulum experiment lab.  This is probably more than anyone in class will submit (even the “A” reports) but it illustrates as an ideal for which one can strive. Notice that it is typed and spell checked, and should not contain errors such as interchanging “affect “ and “effect”.  Typos may be corrected in pen or pencil if they are not too numerous.

In this experiment we investigated the dependence of the period pf a pendulum on two variable, the mass of the bob and the length of the string. We followed the instructions and tried to keep the amplitude constant for all the measurements so that it would not affect the result, because we learned in class that in the case of a pendulum, large amplitude can change the period. We found that changing the mass from 25 grams to 200 grams did not seem to have much effect on the period, so we concluded that the period is independent of the mass.

In the case of changing the length of the string, we used strings from 0.25m to 1.5 m long, between the point of suspension and the center of the bob. There was an uncertainty in the measured length because we had to estimate the center of the bob, and the point of suspension. We believe this error to have been less than 10mm(or 0.01m), so for the 1.5m string the uncertainty was only 0.01/ 1.5= 0.6%, while for the shortest string it was .01/. 25=4%. We assumed that the mass of the string was negligible compared to that of the bob. We measured the period using the clock on the wall for 20 swings. It was difficult to read the time to better than 1 second. So if 20 swings took 8 seconds, an error of one second would be 1/8 or 12%, which would be the largest contributor to the error. If we had used 100 swings for each trial the error would be less but we did not have sufficient time.

When we charted and made a trend line with Excel, the period was proportional to the length raised to the0.45 power. This is to be compared with the value in the text that states that the period is proportional to the square root of the length (0.5 power). This is an error of about 10%, which seems reasonable compared to the timing error.

The experiment could be improved by using wire which doesn’t stretch instead of string, greater number of swings and perhaps a watch readable to better than one second.

(Note to students: errors in results are very seldom below 3% and often 10 or 20% depending upon the apparatus, difficulty of the experiment, and time available.)