Are Force and Extension of Your Slinky Related?

Personal Lab 2

Background

We have learned that a force is required to change the motion of an object. Springs provide a particularly fun way to study changes in motion. The popular Slinky toy is basically a spring, and offers a good example of a combination of motions that will be useful in probing several fundamental science concepts. What causes a spring to extend? What causes a spring to contract? What characteristics distinguish a Slinky from other springs we use every day?

Here you will study different types of springs, and investigate the relation between force, mass and the acceleration due to the Earth’s gravity.

Springs can be classified depending on whether a spring must be extended or compressed to be put in an "active" mode. These two basic types of springs are called extension and compression springs. Into which category did you classify your Slinky Jr.?

Classification is basic to doing science. Frequently we study a large variety of objects, and by sorting and grouping the objects, we can explore patterns and relationships among the subgroups. What additional characteristics can you identify in the springs you studied that you could use to form sub-groups? No doubt you recognized that the "springiness" or "stiffness" of the springs varied greatly.

As in any science, after initial classification into categories and sub-categories, exploration of relationships among variables can lead to the discovery of regular patterns in the way one variable depends on another. Often such studies can lead to fundamental generalizations or laws in nature. Is it possible to predict how far a spring will stretch when a force is applied? Here you will study whether there a basic law that can describe the extent that your Slinky stretches when a force is applied to it. The force will be the weight of pennies suspended from your Slinky. Why is weight considered a force? What causes this force?

Purpose

To find the relation between force and mass of fishing weights using your Spring Scale.

To design and perform an experiment to see if there is a relation between the force exerted by the weight of pennies hanging from your Slinky and the extent that the Slinky stretches.

To investigate sources of error and experimental uncertainties.

Materials

Procedure

Part I: Relation between force and mass of the fishing weights.

1. Examine the springs in your Personal Lab kit. List their similarities and differences. In what ways does the spring in your Slinky Jr. differ from the other springs in your kit? Group the different types of springs, including the Slinky, Jr. and the spring in your Spring Scale, into different categories. List the criteria you used for each category.

2. Use the Spring Scale to find a relation between the amount of pull (that is, the force) (as read on the white scale, given in units of Newtons (N)) and the mass of the fishing weights suspended from the Spring Scale.(The mass of the fishing weight can be read from the black scale on the clear plastic cylinder of your Spring Scale. The mass of an object read from this black scale is in units of grams (g)). Enter each pair of readings of the force and the mass for a range in fishing weights in a Data Table in your Lab Book.

3. Find the relationship between the force of the hanging fishing weight and the fishing weight’s mass, by plotting these two variables on a graph in your Lab Book. Be sure to label both axes in your graph and to give the units of measurement.

Part II: Relation between force and Slinky extension.

4. Find a fairly high place to hang the Spring Scale so that the Slinky can be suspended from the Spring Scale with the tea filter filled with pennies, and not touch the ground. A bent coat hanger held in place by heavy books, and protruding from a tall book shelf is one suggestion for something to hang your Slinky from. Use paper clips to suspend the tea filter bag, so that it can be loaded with pennies.

5. Devise an experiment to find a relation between the amount that the Slinky stretches when different numbers of pennies are loaded in the tea filter bag. Remember that you are investigating whether there is a relation between force (i.e. weight due to the pennies) and the amount the Slinky stretches. You will need to figure out a way to convert "numbers of pennies" to a measure of "force" in units of Newtons.

6. Create a Data Table which summarizes your measurements. Be sure to give headings to each column and the units of measurement for each variable measured.

7. Compare the "amount of pull" or force on the Slinky with the "amount it stretches" by plotting a graph. Be sure to identify which variable you are plotting on which axis, and give the units of your measurements for each variable.

Questions

1. Find the slopes of the relationships found in Parts I and II. Be sure to give units for your slopes, to title your graphs and to label the axes.

2.Explain the meanings of the slopes and their significance.

3. Write separate statements defining what is meant by the terms: force, mass, acceleration due to gravity and weight.

4. Describe in your own words how the slope of your graph in part II indicates the "springiness" or "stiffness" of a spring.

5. List the main sources of error for the measurements you made.

6. The following flow chart¹ summarizes your basic experiment plan for Part II. Complete the flow chart by adding concise statements of your results and conclusions for this Slinky experiment.

1. Taken from Anton Lawson, Summer Workshop on Critical Thinking Approach to Teaching Science, Arizona State University, June 1996.

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Last modified 9 Aug 1997
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URL: http://acept.la.asu.edu/courses/phs110/ds3/pl2.html