Physics Pendulum

                 Enter your results in table C.

Results:

Table A

Length = 20 cm, amplitude = 6 cm

      Table B

      Length = 20 cm, mass of bob constant

Table C

      Mass of bob constant, amplitude of swing = 6 cm

Discussion and questions:

1. Plot a graph of period (T) against length (L) and period against the square root of L. What do these graphs indicate about the relationship between period and length?

The graphs indicate that as the length of the string increases so does the period of motion of the pendulum due to the gravitational force of the earth exerted on the bob mass.  

2. What other factors (not investigated in this practical) may influence the period of a pendulum?

There are many factors that may influence the period of a pendulum that were not investigated in this practical. One of these factors would be natural and artificial wind (air-conditioning), both of these affect the surrounding atmosphere of the pendulum and may influence the rate at which it moves. Another factor is the force at which the pendulum is pushed can influence the movement of the pendulum.

Some abstract factors that may influence the period of the pendulum are the height we are above sea level, because this will affect the density of the air, which will affect the friction of the bob mass. The distance we are away from the equator (the closer we are to the equator the stronger the gravitational force/pull). The orientation (whether it swings North, South, East, West) of the pendulum will be affected by the rotation of the earth.

3. What are the main sources of error in this practical?

The main source of error in the Pendulum practical is the reaction time of the person using the stopwatch. When the stopwatch is pressed, the time on it is inaccurate due to the reaction time of the person pressing it. Inaccurate measures of the length of string, the movement of the pivot point or the amplitude you release the bob mass from are more sources of error.  A major error in this practical is if the person swinging the bob mass accidentally puts more pressure on one swing they have unintentionally affected the outcome of the results for that swing. My group collected our data/results over two days. An error could be found there in the change of the equipment used, (a slightly heavier bob mass, different string, a change of people in timing/measuring/swinging etc).  

4. How could you improve the accuracy of your results?

To improve the accuracy of the results of the experiment have the same person swinging, timing and measuring throughout the whole experiment, will reduce random error. The accuracy of the results could also have been improved by repetition. Repeating the experiment more times and taking the average result of a broader range of results could make the final result more accurate. Conducting the experiment in a building, where the wind flow is minimal will ensure that the motion period of the pendulum is only slightly affected. Using the same equipment used the day before will ensure there are no changes in the experiment due to manufacturing uncertainties.    

Evaluation

This pendulum practical could have proved more successful if the random and systematic errors were cut down, things such as the delay of the person stopping the stopwatch, the pressure the pendulum was released and the exact length of the amplitude were hard to perfect each trial. However repetition pulled us through and the average of the results turned out fairly accurate. When calculating the gravitational force the theoretical value is 9.8 m/s². Our experimental value of the gravitational force was 10.6 m/s². The difference of 0.8 m/s² is possible due to the random errors obtained in the practical or some of the abstract factors (see question two) could have influenced the results.

Conclusion

How does the period of a pendulum depend on...

(a) The mass of the bob

(b) The amplitude of the swing

(c) The length of the string

The time the pendulum takes to complete one oscillation varies depending on the mass of the bob and the length of the string. To show the way in which these varieties of a Pendulum effect the motion period, a series of experiments were conducted. In experiment A, the mass of the bob was changed, going up 50 grams each test. From this particular experiment it was found that the heavier the bob became, the faster the swings became. The next experiment conducted was B, where the amplitude was increased by 2cm. It was shown that as the amplitude was lengthened, the motion of period increased due to the greater distance being travelled by the bob mass.  In C, the length of the string was altered. As the string lengthened by 10cm each time it resulted in the increase in the period of time and motion.

After experiments A, B, and C were conducted, the data obtained was recorded in tables and the square root of the length of the string, the period of motion and length of string were put into graphs.

From these graphs the gravity difference of 10.6 m/s² was worked out. Against the theoretical value our experimental value of the gravitational force was only 0.8 of a difference. This could be due to all the random and systematical errors we stated in our practical.

Through this practical report, it can be concluded that one oscillation of the pendulum is dependent on mass of the bob, the amplitude of the swing and the length of the string.