# Slinky Secrets Revealed

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31-Dec-2015Category

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Slinky Secrets RevealedMath Lab 23

Purpose of LabDemonstrate that the force used to stretch a spring is proportional to the amount it stretches. Find the constant of proportionality.

Math PrinciplesDirect variation, scatter-plot, slope, measuring with a ruler, linear regression.

What Its All AboutThe amount of force (F) needed to stretch a spring varies directly as the amount of stretch (x). The equation that describes this is: F =(const)x.

What Its All AboutIn this lab the stretching force is provided by the weight of nuts hung on the end of a spring (slinky). Since this weight is proportional to the number of nuts, the equation will be modified to the following where N is the number of nuts: N = kx

What Its All AboutMarks will be made on the background (chalk board or white board) as several nuts are successively placed on the hanger. Distances between the marks are measured for later analysis in which the constant of proportionality will be determined.

Slinky Secrets RevealedMark the starting point: With the spring hung with no added weights, stabilize it and mark the bottom of the spring. All measurements will be referenced from this point. Make sure the student marking this and following positions has his eyes level with the bottom of the spring so as to accurately mark the true position.

Slinky Secrets RevealedGently hang one nut on the hanger, stabilize the spring, mark the position, and label with 1. Again, make sure eye level is at the bottom of the spring so as to place an accurate mark.

Slinky Secrets RevealedOne at a time, add nuts (up to a total of four) to the hanger. Each time mark the position of the bottom of the spring and record the number of nuts beside each mark. The picture below shows the marks and labeling after all four nuts have been attached.

Slinky Secrets RevealedMeasure the distances: Using a centimeter ruler, measure the distances of each position of the spring (1, 2, 3, & 4) from the zero mark as shown to the left.

Slinky Secrets RevealedPutting it all together: Make a scatter-plot of the points with a large black marker.

Slinky Secrets RevealedFinding the constant of proportionality: Determine the constant of proportionality (k, also the slope of the line) for this line as follows:

Slinky Secrets RevealedFinding the constant of proportionality: Determine the constant of proportionality (k, also the slope of the line) for this line as follows:

Since the line goes through the origin, use (0, 0) as one point and (36.4, 4) as the other. The slope (and therefore k) is:

Slinky Secrets RevealedFinding the constant of proportionality: Determine the constant of proportionality (k, also the slope of the line) for this line as follows:

Since the line goes through the origin, use (0, 0) as one point and (36.4, 4) as the other. The slope (and therefore k) is:

Since the line goes through the origin, use (0, 0) as one point and (36.4, 4) as the other. The slope (and therefore k) is:

Slinky Secrets RevealedFinally, the complete linear function is:

F = .10989x

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