CHAPTER 3

In the next three experiments you will explore some of the concepts which are addressed by Newton's ideas. Before beginning the experiments, locate the spring scale in your kit and explore what the two scales are, and how the spring scale works. Also review what the scientific experimental procedure is.

The Phenomenon: When we pull on the Slinky, it responds by stretching or extending from its "normal" or equilibrium position. The phenomenon we wish to study in this experiment is the relation between the extent the Slinky stretches which results from pulls or forces of different strengths.

The Question: To focus our attention on a specific aspect of the spring characteristics of the Slinky, we should pose a specific question which we wish to answer. Since we are interested in the amount that the Slinky stretches as a result of different forces exerted on it, we might pose the question: What is the relation (if any) between the extent that the Slinky stretches and the amount of force on the Slinky? Or another way to pose the same question is: Are the force and the extension of the Slinky related?

The Variables: We have now posed such a specific question that we can identify the variables in the experiment we want to perform: The pull exerted or force on the Slinky is one variable. The amount by which the Slinky stretches from its "normal" unextended position is the second variable. Which of these two variables is the independent variable in this experiment?______________________. Which of these variables is the dependent variable?_________________. As the name implies the independent variable is usually the one that you control. The dependent variable is the one that responds to changes in the independent variable.

The Experiment: In some cases we have a model for the phenomenon we are studying in mind before we perform the experiment. However, in this case we have no idea how the amount that the Slinky stretches depends on the strength of the pull exerted on the Slinky. Consequently we will proceed with the exploration of the phenomenon without a model yet in mind. Hopefully the data will contain information, such as a trend or pattern in the variables we measure, that will suggest a model to us.

As a start in planning our experiment, we should first reflect on what it is we wish to measure, and then we should think about the tools we have available to perform a controlled experiment. We will need to measure the extent the Slinky stretches when one end is pulled by different amounts. The extent that the Slinky stretches can be measured with a ruler or meter stick. But how will we measure the "strength of the pull" we apply?

Personal Lab 2: Are Force and Extension of Your Slinky Related?

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