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  • Writer's pictureTerence Pang

O Level Physics Practical - Period of a Pendulum


The period of a simple pendulum is the time it takes for one complete oscillation.


It depends on the length of the string and the acceleration due to gravity, but not on the mass or amplitude of the bob.

The formula for the period of a simple pendulum is:

T=2πsqrt(l/g)

where T is the period, l is the length of the string, and g is the acceleration due to gravity.


To measure the period of a simple pendulum, one can use a stopwatch to record the time for a certain number of oscillations, and then divide by that number to get the average time for one oscillation.


However, there are several sources of error that can affect the accuracy and precision of this measurement. Some of these sources are:

  • Human reaction time: There is a delay between when the pendulum reaches its extreme position and when the person starts or stops the stopwatch. This can introduce a random error in the measurement of time, which can be reduced by using a larger number of oscillations or by repeating the experiment several times and taking the average.

  • Air resistance: The air exerts a drag force on the bob, which reduces its speed and amplitude over time. This means that the period of the pendulum is not constant, but increases slightly with each oscillation. This can introduce a systematic error in the measurement of time, which can be reduced by using a small and dense bob or by performing the experiment in a vacuum.

  • Friction at the pivot: The point where the string is attached to the support exerts a frictional force on the string, which opposes its motion and reduces its speed and amplitude over time. This also means that the period of the pendulum is not constant, but increases slightly with each oscillation. This can introduce a systematic error in the measurement of time, which can be reduced by using a smooth and lubricated pivot or by minimizing the angle of swing.

  • Non-uniform string: The string may not have a uniform thickness or density along its length, which means that its effective length may vary slightly with each oscillation. This can introduce a random error in the measurement of length, which can be reduced by using a thin and uniform string or by measuring its length carefully.

  • Non-point mass: The bob may not have a negligible size compared to the length of the string, which means that its center of mass may not coincide with its geometric center. This can introduce a systematic error in the measurement of length, which can be reduced by using a spherical and symmetrical bob or by measuring its diameter and adjusting its position accordingly.

These are some of the common sources of error for measuring the period of a simple pendulum for O Level Physics Syllabus.


By identifying and minimizing these sources of error, one can improve the reliability and validity of their experiment.

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