CHAPTER 3

You may have noticed that the Slinky appears to stretch uniformly or by the same amount throughout its length. Do the other springs in your Personal Lab behave this way also? You might have therefore decided that you only needed to measure the amount that the lower end of the Slinky stretched from "initial" position as you added coins to the tea filter. Thus one method of approach in planning your experiment would have been to measure the height of the lower end of the Slinky above the floor. You should have recorded the pull on the spring scale at this "initial" position, with only the Slinky plus the paper clips plus the tea filter suspended form the Spring Scale.

At this point in the experiment you should be ready to set up your Data Table which should contain the number of coins loaded in the tea filter, the measured positions of the lower end of the Slinky, the readings of force on the Spring Scale (white scale) in units of Newtons. Note in the sample Data Table below that we have chosen to measure the position of the lower end of the Slinky from the top of a tape measure with one end on the floor and held in a vertical position next to experiment.

Data Table: Sample for Slinky Jr. Experiment

No. of Pennies	Position of Lower End of Slinky Jr. (cm)	Pull of Slinky+Fish- ing Weights on Spring Scale (Newtons)	Displacement from Initial Position (cm)	Pull on Slinky due to Fishing Weights (Newtons)
0	48	0.60	0	0.00
2	55	0.65	7	0.05
4	62	etc...	etc...	etc...
6	etc...
8

We actually made (but do not show in the table) three measurements for each set of pennies. These measurements were recorded in our Lab Book. The positions of the end of the Slinky were recorded to the nearest cm, and the readings on the Spring Scale to the nearest 0.5 Newton. Note that both measurements in columns two and three are given to two significant figures. (See Appendix C for a discussion of significant figures.) After completing all three sets of measurements for different numbers of pennies in the tea filter bag, an average was calculated from the three measurements made for each set of coins. Thus the entries for columns two and three above each represent averages of three measurements. Note that our Lab Book was used for recording the initial measurements or "raw data". The averages of three measurements were calculated, entered in our Lab Book, and then also entered in the Data Table. Why do you think we took three readings for each measurement?

After entering the average values for the measurements, we then converted the data to a more meaningful form. Column four gives the differences in positions of the Slinky from the initial position, and column five lists the differences in the amount of pull registered by the spring scale between the unweighted Slinky and the Slinky when weighted by one or more coins in the tea filter. Note, then, that column four gives the extent that the Slinky stretched from initial position. Column five gives the added amount of pull due to adding weight (coins in the tea filter) to the Slinky. Why did we choose to form these differences?

At this point you may wish to read about additional comments on:

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