Sunday, August 23, 2009

Scientific Method: What Affects a Pendulum's Swing?

Before scientists can find answers to their questions about nature, they first must actually pose the question in a manner that can be answered. They must do research to see if anyone else has already answered that question to their satisfaction. Then they must form a hypothesis, an educated guess, to try to answer the question.

Next, they must design an experiment so that they can test their hypothesis. Designing an experiment includes deciding what materials they will need, what the dependent and independent variables are, what the constants are, and what the control will be.

Variables are the factors in the experiment that will change as the experiment goes on. The independent variable is the thing the experimenter is testing. He decides what the values are going to be in advance. The dependent variable is the factor that changes in response to the independent variable. The constants are factors that do not change. And the control is what the results are compared to.

In the lab we did in class in which we made pendulums, our question was, “What determines the rate at which a pendulum will swing?” Students were asked to formulate a hypothesis that might include any or all of the following variables: length of the string, the amount of weight on the pendulum, or the starting angle (how far the pendulum weight was drawn back). Which one of these variables would affect the rate of swing?

Different students had different hypotheses. Some predicted the rate would be affected only by the length. Others hypothesized that all three factors would affect the rate. And some picked various combinations of two factors.

Our materials included large washers to use as weights, a string measuring 100 cm, a timer, and a meter stick.

We constructed a pendulum by placing a washer on the string and doubling it so that it was 50 cm long. We then set the pendulum in motion and counted the number of swings in one minute. We repeated the procedure for 30 cm and 15 cm lengths of the string. We recorded our results on a table.

In the second part of the experiment, we left the string at 50 cm and timed the pendulum for one minute for each of three weights. We added one washer at the end of each trial. The results were recorded in another table.

Finally, we did two trials in which will kept the weight and length the same, but varied the angle at which the pendulum was pulled back. Again, the results were recorded.

Our conclusions were that the length of the string did affect the rate of swing. We found that the shorter the string, the faster the swing. On the other hand, neither the weight nor the angle affected the rate of swing.

So those students who hypothesized that only the length of the pendulum will affect its rates confirmed their hypothesis. Hypotheses involving other combinations of factors were refuted.

In our experiment involving the length of the pendulum, the length was our independent variable. It is what we controlled. The rate was the dependent variable. Constants included the weight at the end of the pendulum and the angle of the swing.

In the experiment testing for the effect of weight, the weight was the independent variable. Again, the rate was the dependent variable and the constants were the length of the string and angle.

The experiment testing how the angle affected the rate, the angle was the independent variable. The rate was again the dependent variable. Constants were the length of the string and the weight.

Our control was a pendulum with a 50 cm length and a single washer for weight launched from a 45 degree angle.

Students wrote up their results in a report.

The scientific method was followed throughout:

1. We started with our question and a little background information about pendulums.
2. We stated our hypotheses.
3. We designed and then conducted an experiment to test our hypotheses.
4. We came to a conclusion.
5. We wrote up our results for presentation.

1 comment:

Hannah said...

Thanks! This really helped! It gave me ideas for my own experiments and showed me how to set out my experiment.