Q
8 washers, #8
VOCABULARY
Q
A wide permanent marker in any color that will contrast with the
wood
Q
Poster paints: red, green, blue, black, and white, and 5 brushes
Amplitude:
a measure-
ment of the energy of a
wave. Amplitude is the
displacement of the
(
optional
)
for each small group
Q
One copy of Master 4.3b, BOSS Worksheet
Q
Pencils or pens
Q
Stopwatch
Q
Meter stick
P ROC E DUR E
Teacher Preparation
Build the BOSS model by following the directions on Master 4.3a.
Practice with your model until you’ve got a feel for each frequency
and you can get any of the rod assemblies to resonate. One technique
is to use a firm push first, then watch the number you want and wiggle
the base very lightly at its natural frequency to get resonance.
A. Introduction
Find out what students already know about the concepts of amplitude,
frequency, and resonance. If they are not familiar with these terms,
introduce them by building on what students already know from other
areas. They may know, for example, that resonance and frequency are
used in describing the tone of musical instruments and the quality of
sound produced by different recording techniques and players. The
phenomenon of resonance also accounts for laser light and for the
color of the sky.
B. Lesson Development
1. Direct students’ attention to the BOSS model, and explain its name.
Ask the students to predict which numbered rod assembly will
oscillate the most when you wiggle the base. Have them hold up 1, 2,
3, or 4 fingers to indicate their prediction. (They will probably say
number 1 because it is the tallest.)
2. Oscillate the BOSS model so that some rod assembly resonates
other than the one most students predicted. This will baffle the
students, so let them predict again. Again make the rod resonate for an
assembly they did not predict. Finish this demonstration after several
tries by making the rod resonate for the assembly most of the students
did predict, so that they get it right. Invite discussion.
3. Relate the blocks and rods to buildings of various heights in an
earthquake. Ask students if they think buildings would oscillate like
this in an earthquake. (They always do, and in some earthquakes the
effect is especially pronounced. In the 1985 Mexico City earthquake,
the ground shaking resonated with the natural frequencies of 8-to-10-
medium from zero or the height of a
wave crest or trough from a zero
point. (In this activity it’s how far to
the side the block moves.)
Frequency:
the rate at which a
motion repeats, or oscillates. The
frequency of a motion is directly
related to the energy of oscillation. In
this context, frequency is the number
of oscillations in an earthquake wave
that occur each second. In
earthquake engineering, frequency
is the rate at which the top of a
building sways.
Hertz (Hz):
the unit of measurement
for frequency, as recorded in cycles
per second. When these rates are
very large, the prefixes
kilo
or
mega
are used. A kilohertz (kHz) is a
frequency of 1,000 cycles per
second and a megahertz (MHz) is a
frequency of 1,000,000 cycles per
second.
Oscillation or vibration:
the
repeating motion of a wave or a
material—one back and forth
movement. Earthquakes cause
seismic waves that produce
oscillations, or vibrations, in
materials with many different
frequencies. Every object has a
natural rate of vibration that
scientists call its natural frequency.
The natural frequency of a building
depends on its physical
characteristics, including the design
and the building materials.
Resonance:
an increase in the
amplitude (in this case, the distance
the top of a building moves from its
rest position) of a physical system
(such as a building) that occurs
when the frequency of the applied
oscillatory force (such as earthquake
shaking) is close to the natural
frequency of the system.
A G U
/
F E M A
249
S
E I S M I C
S
L E U T H S
