Waves and Radiation NOTES

Research Question: Is it possible to verify the earth’s gravitational field strength at Istra and get results that are close to the text book result (9.8ms-1)? Hypothesis: I believe that it is possible to verify the earth’s gravitational field strength at Istra just like you can verify it wherever you are in the world. There are several ways in which this can be done due to the fact that g (gravitational field strength) is met in various equations.

However, the most valid experiment in which we can find g is the pendulum one due to the fact that it is possible to do it at Istra and at the same time get a fairly accurate result. A pendulum is made up of a mass (bob) attached to a string that is fastened so that the pendulum can swing (oscillate) in a plane. In a simple pendulum, all the mass is considered to be concentrated at a single point at the centre of the bob. Physical quantities of the pendulum include length L, mass m, angle through which the pendulum swings ?, and the period T of the pendulum (which is the time it takes for the pendulum to swing through one complete oscillation).

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The equation above is the equation we will be using to try and verify the gravitational field strength at Istra. T is the period of 1 oscillation, 2? is a constant alongside with g which is the acceleration due to gravity and L is the length of the string. In our experiment we will find T and L which will leave us with a constant. Once we find the constant, we can then calculate g. To make this equation simpler i.e. to find g easier it is more convenient to square both sides.

Variables: Independent variable: The independent variable in this experiment will be the length of the string because we will be changing it. Dependant variable: The dependant variable is the Period of the pendulum Controlled Variables: There are several variables which we need to take control of. First of all, we will keep the same mass throughout all the experiments by simply using the same load. We will try and keep the angle at which the pendulum is dropped from the same by tying another string at an angle next to the one we use and by making sure that we leave the mass from the same point every time. Also the string used will be the same type i.e. only the length of it will vary.

1. Find an area where there is a small playground which you can use to tie the string. 2. Tie the string to the load or ball. 3. Measure a certain length of the string and tie the string on the metal bar. 4. Next to the string that you tied, tie another string at a small angle and hold the end of it with the retort stand so that it doesn’t move. 5. Lift the string with the load on so that it matches the other string that you just tied i.e. so that they have the same angle. Use a spirit level or ruler to make sure that the two string are in line.

6. Leave the load and time one oscillation (this means that it must go forward and come back to the original position). 7. Now untie the string and use a longer piece of string. Repeat steps 3, 4, 5, 6 making sure that you are using the same ball and the same type of string. 8. Again, when you timed one oscillation untie the string, get a longer piece and repeat step 3, 4, 5, 6. Do these as many times as you need. Method of Collecting Data:

1. First of all, if you have enough space, use a string with 50 cm intervals. In other words first measure the period with a 50 cm string, then with 1 m string, then with 1.5 m, etc. 2. Instead of timing straight away, allow the load to swing about five times to get more accurate timing on start. 3. Time 20 oscillations and then divide your answer by 20 in order to get a much more accurate result. 4. Make people help you.

Let one person leave the mass, and two other people start stopwatches in order to get more readings and hence more accurate results. 5. Do about three trials for each length in order to calculate averages and get a much more accurate result. 6. Write all your results in a table and then draw graph to see the correlation between T and L. Data Collection and Processing Data collection: Table showing the Period for 20 oscillations obtained at different lengths. (All time readings to two decimal places).

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