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The case of the trembling table: this month, learn about detecting earthquakes.

Characters

Narrator 1

Narrator 2

Todd

David

Erika

Narrator 3

Ali

Narrator 4

Narrator 1: The science fair is today. Todd, Erika, Ali, and David are setting up their science projects on a long table. Todd is at end of the table. His battery experiment is incomplete.

Todd: I guess I won't win.

Erika: I might. My experiment testing plant foods worked really well.

Narrator 1: Todd notices Ali setting up on the other side of Erika. A cone-shaped structure with a hole in the top rests on the table.

Todd: That looks neat, Ali.

Ali: I made a volcano. It has baking soda inside. When I add vinegar to it, it erupts!

Todd: Wow, I bet you'll win.

Shake and Quake

Narrator 2: Next to Ali, David places a cardboard box on the table. A cup with a marker stuck through the bottom hangs inside the box.

Ali: What's that, David?

David: It's a seismometer, a device that measures vibrations. Scientists use them to detect the vibrating energy waves that travel through the ground during an earthquake.

Erika: How does it work?

David: I pull paper through the seismometer. If there's a vibration, the marker shakes and draws a jagged line on the paper.

Narrator 2: Ali noticed some paper on the table. Some of the pieces have jagged lines on them. Others have relatively smooth lines.

Ali: Why are the lines different?

David: It depends on where the vibration occurs. If it occurs nearby, it will create a jagged line. If it occurs far away, a smoother line will form. The lines that seismometers make help scientists determine how far away an earthquake is.

All Shook Up

David: The judges will be at our table soon. I am going to test my seismometer.

Ali: I can't test my experiment. I have only enough vinegar for one eruption.

Narrator 3: Just then, Erika bumps into the table while arranging her plants. Ali grabs her cup of vinegar before it tips over.

Ali: Watch out, Erika! If my vinegar spills, I won't be able to show my experiment.

Narrator 3: Ali places the cup back on the table. A second later, the table shakes again. A little vinegar sloshes onto the table.

Ali: Erika!

Erika: Todd shook the table. He's still finishing his project.

Ali: I'm going to clean this up before the judges come over.

Tipped Over

Narrator 4: When Ali returns, she finds her cup of vinegar lying on its side. Vinegar covers the table.

Ali: Oh, no! I told you to be careful, Erika. You bumped the table and knocked over my vinegar.

Erika: It was Todd again!

Todd: I didn't do it.

Narrator 4: Ali stares at them. Erika is right next to Ali's volcano. Todd is at the opposite end of the table, farthest from David.

Ali: David, weren't you just testing your seismometer?

David: Yes, here's the reading.

Narrator 4: Ali looks at the piece of paper and sees a very jagged line.

Ali: I know who did it!

Solve the Mystery:

Who knocked over Ali's vinegar?

To solve the mystery, grab these materials: paper cup * scissors * marker * piece of string, 45 centimeters (16 inches) long * large cardboard box, empty with the top flaps cut off * meter stick * dried beans * long table * paper

1. Build a seismometer (see diagram). Have an adult poke three holes in a paper cup: one in the center of the cup's bottom and two holes opposite each other along the cup's rim. Put a marker through the hole in the bottom of the cup. The writing end should stick out of the bottom. Thread a piece of string through the two holes in the rim of the cup. Place an empty box on a table so that the open end faces you. Have an adult poke two holes one inch apart in the top of the box. Thread the ends of the string from the cup through the holes in the box. Position the string so that the marker in the cup is just touching the bottom of the box. Tie the string. Fill the cup half-full with beans to weigh it down.

[ILLUSTRATION OMITTED]

2. Use your seismometer to find out who knocked over Ali's cup. Place the seismometer on one end of a long table. Place a sheet of paper in the box so that the marker is touching it. Have a partner pull the paper slowly out of the box while you bump the table at a point 60 centimeters from the seismometer. Note the line created on the paper. Place a clean sheet of paper in the bottom of the seismometer. While your partner pulls the paper, bump the table with the same amount of force as before, but standing 1.8 meters away from the seismometer. Note the line created. Whose table bump would have created the line that knocked over Ali's cup?

THE CASE OF THE TREMBLING TABLE

ESTIMATED TIME: 50 minutes

BEFORE READING

Set a Purpose

Read a fictional mystery to learn how scientists detect earthquakes.

Background

* A seismometer, also known as a seismograph, is an instrument that measures the vibrations of an earthquake. The record made by the seismometer is called a seismogram.

* The point in the Earth's crust where an earthquake starts is called the focus. The point on Earth's surface that is directly above the focus is called the epicenter. That's the earthquake's point of origin on the surface.

Discussion Question

* What is a science fair? Have you ever participated in one, and if so, what was the experience like? (Answers will vary.)

AFTER READING

Conclusion

* When someone bumped into the table, the resulting vibration knocked over Ali's cup of vinegar. The vibration was recorded by David's seismometer. The line that came out of the seismometer was very jagged. This means that the source of the vibration was very close to the seismometer. Erika set up her science fair project closer to the seismometer than Todd did. Therefore, we can can conclude that Erika is the one who bumped into the table and knocked over the cup.

Discussion Question

* What type of line would be created on a seismometer if an earthquake occurred far from the Location of the seismometer? (Answer: a slightly jagged line)

RESOURCE

Check out earthquake-related games, information, and activities at this site: http://earthquake.usgs.gov/learn/kids/
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Title Annotation:science mystery
Author:Leach, Ben
Publication:SuperScience
Geographic Code:1USA
Date:Sep 1, 2011
Words:1063
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