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Sensing and Datalogging for Science Education |
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Sciencescope |
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Last updated 2nd July 2009 Sensors Logbooks UK PriceLists Investigations 2009 Catalogue |
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Earthquake wavesThere
are four kinds of wave produced by an earthquake. Two move over the surface,
causing damage, and two pass through the Earth itself: body waves. By studying body waves, scientists have worked out what the Earth is like inside:
Body
waves tell us a great deal about what we cannot see inside the planet. -
P-waves: Primary waves are longitudinal
waves that push and pull the earth. They are the fastest body wave,
averaging speeds of about 6 km/s and so arrive first. -
S-waves: Secondary waves are transverse
waves, which make the earth shake from side to side. Slower than P
waves, they average about 4 km/s and so arrive second. Both
S and P waves travel throughout the body of the earth, and can be picked up by
seismometers - machines that record earthquakes - anywhere in the world. However,
it turns out that S waves cannot travel through the core, and only P waves are
recorded in some places:
A seismometer records the vibrations from earthquakes. Mechanical
versions work by way of a large mass, freely suspended. In
the example on the right, a rotating drum records a red line on a sheet of
paper. If the earth moves (in this case from left to right) the whole machine
will vibrate too. However,
the large mass tends to stay still, so the drum shakes beneath the pen,
recording a squiggle. The
confiner prevents the mass from bouncing around all over the place. Incidentally,
a seismograph is the graph that a seismometer draws.
You are going to simulate a seismometer.
View and/or download the worksheet View and/or download the Datadisc file example of this investigation. (you must have Datadisc installed to view the file, downloadable from Download Centre) |
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