单摆实验英文报告.doc

THE SIMPLE PENDULUM: A CLASSIC CASE STUDY The purpose of the simple pendulum is to research the factors of period and measure the period. In order to do this experiment, we should prepare for some materials include some different pendulum bobs with different mass, a long pendulum string, a pencil, a mobile phone with a stopwatch, a ruler and an inclinometer. Our team chooses an iron bob and a copper bob. We think the heavier bobs can help us finish this experiment. Of course, it doesnt have a work. Firstly, we make the long string through the copper bob, and tie the bob. Then, we put the string around the pencil, so we can control the length of string optionally. Lastly, we put the pencil on the side of the table. A simple pendulum apparatus is finished. After finishing the apparatus, we started to do the experiment. What are factors will influence the period? There will be three factors: the angle between the original position of string and upright, the mass of bob and the length of pendulum string. Therefore, we control the incidence angle is 30 degrees and the length of pendulum string is 20 centimeters in the first experiment. When one member releases the copper bob from the original position, another member starts the stopwatch. After the bob finishes 30 cycles, the member stops the stopwatch right now. The number on the screen is the time for 30 cycles. Then we change the angle and length and bob to repeat the steps we finished just now. When we finish all the steps, we have some different records, and we draw a chart for the records.This is the chart.numberMass of bob(gram)Angle(degree)Length(cm)Time(second)1Copper 7230 20 28.2662 72 20 20 28.1053 72 10 20 27.9244 72 10 30 32.800 5 72 10 40 37.1506Iron 95 10 20 28.1177 95 20 20 28.109895 30 20 27.986Now, we should analyze these data. First of all, we look at the number 1 to number 5. We just use a copper bob. In other word, we cant change the mass of pendulum bob. From number 1 to 3, only the angle is changed. When we change another bob, the time has no change. We can say that maybe the angle is not the factor, but we should have a father analysis. Compared number 3, number 4 and number 5, we find that the time changes with the changing of length of bob. So, we can have a conclusion that the length of bob is one of the factors. At present, we will explore the connection between the mass and period. So we keep the angle and length constant and change the bob, an iron bob. Taking the data of number 3 and number 6 together, we can obviously see the time is same (just has a little difference). We also could put number 2 and 7 or number 1 and 8 together, the time is not change. From the above analysis, we may have a conclusion only the length of string is the factor which can change the period of the simple pendulum. In order to let us have a clearer feeling, we draw some graphs.In the process of analyzing data, we notice that the data should be same rather than similar. Why is the time different？the reason is that this experiment has random error. When we do this experiment, we just stop the stopwatch by our feeling. We cant stop the stopwatch accurately when the bob arrives at the original position. In addition, we also cant start the stopwatch accurately. As a result, we will choose to measure the total elapsed time for 30 full cycles, and then, figure out the time for each swing cycle. It is the period we want to research. When the little ball comes back to the original position, at the time, the ball is resting. But you cant see the ball didnt move in you eyes or your feeling. So you cant stop the chronograph at that time accurately. Hence the data is not very accurate. In other words, the error is much bigger. If you choose to measure the 30 cycles time, you can reduce the error as far as possible.In the end, we should give a conclusion for this experiment. The period is influenced by the length of pendulum string. For the farther, we can also find out that an expression about the period: T = k*L1/2. The k is a constant number which not affected by this experiment. If we want to determine the number, we should have more experiments. After the experiment, we do an evaluation. Because