Teacher Resource - Activities
Experiential Science 30—Freshwater Systems
Activity 6 Illustrating the Principle of the Seismograph
Time
• 30 minutes
Activity Type
• lab
• research team
S T U D E N T B O O K P. 85
Materials and Equipment
• Each research team needs: plumb bob or weight; string (about 60 cm long); frame or
ring stand; sheet of paper; soft lead pencil, sharpened; tape
Teaching Suggestions
• One student will need to move the frame, and the rest can observe. Encourage students
to take turns in these roles.
• Alternatively, set up this and other simulation activities as stations in the classroom
and provide several class periods for student teams to circulate through the stations,
experiencing them all. This activity could also be presented as a demonstration by
volunteer students.
• For a more open-ended activity, provide student teams with access to various lengths
of string and sizes of weights, as well as the stand. Ask them to design a model to illustrate how a seismograph works. In doing so, they should also explain why they chose
the length of string and weight size.
• You may wish to discuss with students the evolution of instruments from mechanical
models (mechanical pendulums and strings) to electronic instruments that rely on
electronic accelerometers, which can withstand more intense earthquakes than a sensitive seismograph. They provide detailed information on acceleration, velocity, and
displacement.
Procedure—Expected Results
4. The pendulum follows the movement of the stand, marking the paper in a line whose
length is related to the force of swinging the frame.
5. The swing of the pendulum is amplified.
Reflections and Conclusions—Suggested Answers
1. The motion of the pendulum will respond to the external forces in a predictable manner. Once a force is applied and the stand moves, the pendulum will remain at rest
as the frame moves underneath it. This results in the pen at the end of the pendulum
making a mark on the paper that represents the amount of displacement. The length
of the pendulum and how it behaves will be reflective of the frequency at which the
movement is taking place.
2. This simple set-up is much the same as a seismograph. A seismograph uses a weighted
pendulum to record the movements of the Earth. As the ground moves back and forth,
the pendulum reacts by remaining stationary. The movement is recorded on the seismograph, which records the relative motion of the Earth as it moves back and forth
and/or up and down. A misconception is that an earthquake causes the pendulum to
move, but the pendulum remains fixed and the Earth moves beneath it.
3. This demonstration shows the effects that period and resonance will have on the relative motion of an object. In this case, the activity shows how an understanding of the
swing period of a pendulum can be used to build a seismograph, which can help you
observe and understand earthquake movement.
4. Answers will vary; however, students should be able to suggest ways to increase accuracy in processes such as testing and retesting for reproduction of the same results,
trying different lengths of pendulums, or testing different weights of pendulums.
Chapter 2 Seismology
5. Answers will vary; however, students should be able to suggest that the wave of an
earthquake over time could be recorded by using a moving sheet of paper or paper
wrapped around a rotating drum. As the paper moves beneath the pencil, it will record
the wave of the earthquake over time.
Scientist’s Toolbox—Strong-Motion Accelerograph
S TUDE NT B O O K P. 8 7
• Discuss the definition of acceleration with students and how acceleration can be used
to better understand earthquakes. This is also an opportunity to talk about “asking
the right questions.” In an earthquake, should we monitor the general movement of
the ground, or its acceleration in the x-, y-, and z-planes? Which will give us “better”
information about what is going on during an earthquake?
• Ensure that students understand the difference between accelerometers, accelerographs, and accelerograms. An accelerometer is a device for measuring acceleration.
An accelerograph is a device that measures shaking during an earthquake; it is a type
of seismograph. An accelerogram is the printed record produced by the accelerograph.
• Show students images of accelerograms, available by searching for “accelerogram” online.
• Hold a class discussion on how an accelerograph contributes to our knowledge of
earthquakes. Have students compare what this instrument measures and what a seismograph measures.