Independent variable: The length of the string of the bob
Dependent variable: Period of a swing of the pendulum
Control variable:
-The string of the pendulum,
-The mass of pendulum,
-The level of wind,
-Angle of releasing the pendulum
Apparatus used:
2 Stands
3 Clamps
3 Boss heads
1 Protractor
1 String
1 Pendulum
1 Ruler
1 Data-logger
2 Wooden clamps
1 Timer
Method:
Measuring the variables:
To measure the length of the string, it is better to use a long, straight ruler to obtain the data; we should straighten the string and then put it besides the ruler. Measure the length from the bottom that hangs the bob to the required length, and then mark it with a pen. Whenever we have to change the length, just do the same way followed by marking the point with a pen.
In order to minimize the error, we chose to use the data-logger in which electronic is always more accurate than human hands. But we still use a timer and time by hand to do a double check.
Controlling the control variables:
We use the same string, the same bob (same pendulum) throughout the whole experiment so as to keep the quality and condition of the pendulum are the same. As well as we constructed the experiment indoor without windows or doors open, so no wind is blowing at that moment, if there was wind blowing, that would totally affect the accuracy as the swinging would not only depend on the releasing force but the blow. Lastly we used a protractor to make a clear angle from releasing.
We repeated the experiment 3 times for 8 different heights from 10 cm to 45 cm of the string, 5 cm increased in length each time, measuring 10 periods of the pendulum.
Result of the experiment:
Graph obtained:
From the graph, by T=2(π^2)√(x/g), we can see, the longer the string, the longer time the pendulum needs to complete a period.