Earth Science Today, Earthquake and wave lab (takes about 80 minutes)

We can't go down deep into the Earth.  What's more, we can't even see into the Earth.  How do we know what's there?

We "hear" into the Earth.

Waves travel through the Earth.  They slow down or speed up and bend in characteristic ways that tell us what the inside of the Earth is like.

Puzzle #1:  On the mysterious planet hcratsnroc, there are only two kinds of material, plain water and water plus cornstarch.  An earthquake happens on this planet and the shock waves travel 45 inches (everything is smaller on hcratsnroc) to your city.  It takes them 4.9 seconds to reach you.  You learn that the shock wave takes only 4.6 seconds to reach another city that is equally distant from the earthquake but in the other direction.  Your challenge is this, is the material between you and the earthquake mostly PLAIN WATER or is it CORNSTARCH WATER?

Your materials are these:  a ruler, a stop watch, a kitty litter tray, 400ml of plain water, and a 400ml mixture of water plus cornstarch (put 200ml starch in a beaker, then add water, mixing until entire mixture is 400 ml).  Keep cornstarch well mixed!

Hint:  to see when a wave "arrives" at its destination in your kitty litter tray, you can move your head until you see the reflection of one of the overhead lights at the spot in the water you want to see the wave.  Then, when the wave passes, you can clearly see the lights ripple. You will need to practice to get good enough to make accurate measurements. You can get a good straight wave by tilting the tray slightly, then letting it fall back.

This puzzle illustrates the conceptual way in which we figure out what kinds of materials are in the Earth under our feet.

Puzzle #2:  A twisting wave takes just a little over 2 seconds to travel from one end of a rubber band-toothpick string to the other.  How many rubber bands are in it?

Hint:  make your own and see how fast the wave travels! Twist the toothpicks on one end several times and see how long the twisting motion takes to travel to the other end.

This puzzle illustrates the conceptual way by which we figure out how deep in the Earth different features (such as the core) are.

Prizes:  A bag of peanut M&M's to the team that solves the first puzzle correctly AND is the closest of all teams to the correct number of rubber bands.

grades:  50% of the lab grade for part 1, with explanation of your experiment, results and reasoning
50% of the lab grade for part 2, with explanation of your experiment, results and reasoning.
(lab report due in one week, this particular lab report can be fairly brief, perhaps a page or page and a half needed to explain what you did, what the results were, and how you interpreted the results).

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