Question

Hi! I have some questions I'd like to discuss regarding an experiment with the pendulum

I will have a laboratory class in which I will have to measure the period of oscillation of the swinging pendulum using an electronic stopwatch.

what method could I use to obtain the period of a physical pendulum using a stopwatch, taking care to minimise any uncertainties?

Can you help me to go through this questions?

Should you start the stopwatch at the same time as you set the pendulum swinging, or would it be better to start the pendulum swinging and begin timing later?

Will you measure the time for just one “to-and-fro” swing (i.e. one period), or the time for multiple swings and then divide the time by the number of swings to get the period?

How many measurements will you make at a particular pendulum length? Would it be better to take the average of several measurements?

What angle will you be using? Why?

What is the uncertainty in the length of the pendulum? Is it limited by the precision

of your equipment or something else?

What is the minimum length that you will be using? Why?

Answer 1

1) as the measurement of period is dependent upon the person who is taking the measurement (because he has to decide at which point , he will mark the starting point and to determine the exact time when the bob comes back to the starting point and stopping the stopwatch at that exact moment).

so it is impossible to get an accurate reading in only one swing of the bob. so best way is to let it oscillate for multiple time , say 10 or 20 and measure the total time taken for the same and calculate the time period as time measure/number of rotations.

2) question:Should you start the stopwatch at the same time as you set the pendulum swinging, or would it be better to start the pendulum swinging and begin timing later?

answer: better to let the pengulum fall from a high point and start the stopwatch when the bob passes through the middle point. To make the middle point as accurate as possible, better to place a vertical scale just behind the pendulum so that you can decide the exact moment when the pendulum passes the vertical position.

Q3.Will you measure the time for just one “to-and-fro” swing (i.e. one period), or the time for multiple swings and then divide the time by the number of swings to get the period?

answer: As i have mentioned in the beginning , determining only for one "to-and-fro" movment, the error may be high due to human imposiblity to stop the watch at the exact moment when the bob passes through the starting point. so take measurement for several times, say 10 or 20 to measure the total time period and get single time period=total time period/number of oscillations.

Q4.How many measurements will you make at a particular pendulum length? Would it be better to take the average of several measurements?

answer: the number of oscillations for the measurement depends on your choice. first check with 5-10 oscillations and compare your results with theoretical calculation. if the readings vary largerly, try to increase the number of oscillations.

Yes, it is better to take average of multiple oscillations.

Q5.What angle will you be using? Why?

answer: A medium angle (between 40-60 degrees with vertical) will help as small angle will result in smaller oscillations and large angle may affect the observation of first few oscillations due to high speed.

Q6.What is the uncertainty in the length of the pendulum? Is it limited by the precision

of your equipment or something else?

answer: it is limited by the equipment.

Q7. What is the minimum length you will be using?

answer: again that depends upon your lab set up and your avaialbility of precision instruments and their range.