Station 4: Spring Action
Rube Goldberg Machine Design Contest Teacher Training Program
January 27, 2007
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 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 force to tighten itself.
Image borrowed from MIT's 2.007 webpage:
http://pergatory.mit.edu/2.007/contests/2007/html/kit.html
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. The air in a screen door piston behaves as a spring
because it provides a spring-like cushion. A cantilever beam, such as a yardstick held against a
table surface, oscillates back and forth like a spring (think of a divingboard). 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. Familiarize yourself with the different types of springs: extension, compression, and
torsion.
2. Measure the natural length of one of the extension springs. Hang it on the hook.
3. Hang a calibrated mass on the other end of the spring and measure the new length.
Record the mass in the table.
4. Calculate the amount the spring stretched.
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5. Apply Hooke's law (F=kx) to determine the spring constant k.
6. Repeat steps 2-5 for two more extension springs. What is the relationship between k and
the stiffness of the spring?
Weight (N) Natural Length (m)
Extended
Length (m)
Difference (m)
Spring
Constant (N/m)
Trial 1
Trial 2
Trial 3
Section B
7. Choose a compression spring and a weight.
8. Measure the natural length of the spring in meters. Put the weight on the platform atop
the compression spring and measure the new length. Record the length measurements
and the mass in the table.
9. Put another calibrated mass on the platform and measure the new length. Record mass
and new length values in second row in the table.
10. Repeat for a one other mass. Calculate the spring constant. What’s the relationship
between the spring constant, the spring length change, and the mass (i.e. force applied)?
Weight (N)
Natural Length (m)
Compressed
Length (m)
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Difference (m)
Spring
Constant (N/m)