Station 4
Spring Action
Rube Goldberg Machine Design Contest Teacher Training Program
January 29, 2005
Introduction
Springs are found everywhere, from the cushions in your sofa seat to the shock absorbers in your
car, you name it! Springs can transmit a lot of force, and can store energy. At this station, you
will be taking a closer look at the types of springs, their characteristics, and possible applications
within your machine.
Background
A spring is usually a coil of wire that wants to retain its coiled shape. If you squeeze it (compress
it) with your fingers, it exerts an equal force back on your fingers. When you let go, it returns to
its original shape. Similarly, if you stretch a spring (extend it), it will exert an equal and opposite
force to tighten itself. The force that the spring exerts on an object is directly proportional to the
amount that the spring is stretched or compressed, which can be expressed mathematically as
F=kx, where k is the proportionality constant and x is the amount that the spring is stretched or
compressed.
There are many different types of springs, and virtually anything can be modeled as a spring. For
example, the air in a screen door piston can be modeled as a spring because it provides a springlike cushion. A cantilever beam that oscillates back and forth also behaves like a spring (think of
a diving springboard). The springs that we will be focusing on are extension springs,
compression springs, and torsion springs.
Experiment Time!
Purpose
The supplies kit for the Rube Goldberg Machine Design Contest contains a lot of springs, so you
should learn to use the springs to your advantage. In this experiment, we will focus on
identifying different types of springs and developing an understanding of spring constants.
Procedure
Section A
1. Open the box of springs and familiarize yourself with the different types (extension,
compression, torsion, different lengths and diameters)
2. Open the box of mystery springs and sort them by type (compression, extension, torsion)
3. Measure the length of one of the extension springs. Then hang it on the hook.
4. Hang a calibrated mass on the other end of the spring and measure the new length.
Record the mass in the table.
5. Calculate the difference in length.
6. Apply Hooke’s Law (F=kx) to determine the spring constant.
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7. Repeat steps 3-6 for two more extension springs. A stiffer spring corresponds to what
kind of spring constant value?
Mass
Weight
Natural Length
New Length
Difference
Spring Constant
Section B
1. Choose an extension spring and a calibrated mass.
2. Measure the natural length of the spring. Hang the calibrated mass on the end of the
spring and measure the new length. Record the length measurements and the mass in the
table.
3. Hang another calibrated mass on the end of the spring and measure the new length.
Record both values in the table.
4. Repeat for a few other masses. Calculate the spring constant. What’s the relationship
between the spring constant, the spring length change, and the mass (i.e. force applied)?
5. Repeat for another spring.
Mass
Mass
Weight
Weight
Natural Length
Spring 1
New Length
Difference
Spring Constant
Natural Length
Spring 2
New Length
Difference
Spring Constant
Now you can design your own experiment with the springs!
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