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# Pushing and Pulling: Why are More Volcanoes Found in Areas of Great Crustal Movement?

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Source:
Author: Janice VanCleave

### PROBLEM

Why are more volcanoes found in areas of great crustal movement?

### Materials

• sheet of typing paper
• quarter
• pencil with new eraser
• thermometer
• timer
• helper

### Procedure

1. Place the sheet of paper on a table, and lay the coin in the center.
2. Draw an outline around the coin. Remove the coin when you are finished.
3. Lay the thermometer next to the paper.
4. Allow the thermometer to lie undisturbed for five minutes and then read and record the temperature.
5. Press the pencil eraser against the thermometer bulb for ten seconds. WARNING: Be careful not to press so hard that you break the bulb.
6. Read and record the temperature shown on the thermometer. Do not touch the bulb with your fingers.
7. Ask your helper to start the timer as you rub the eraser back and forth against the paper inside the circle. Rub as quickly and as hard as possible without tearing the paper.
8. Stop rubbing when your helper notifies you that ten seconds have passed.
9. Immediately, gently press the eraser against the bulb of the thermometer (as before, take care not to press so hard that you break the thermometer).
10. Observe the thermometer.
11. When the temperature reading stops changing, read and record the temperature.

### Results

The temperature reading increased when the bulb of the thermometer was touched by the eraser after the eraser had been rubbed against the paper.

### Why?

Moving one surface against another, such as the eraser against the paper, causes friction. Friction is a force that acts against motion, and this resistance to motion produces heat. The increase in the temperature of the eraser was a result of the friction produced by the pushing and pulling motion of the pencil eraser against the paper.

According to the plate tectonic theory, the crust of the earth is broken into large plates that float on a hot fluid. Volcanoes and earthquakes occur along boundaries where plates collide. It is now understood that large amounts of heat can be produced when one great, massive crustal plate moves against another crustal plate. This crustal movement causes friction, friction produces heat, and the heat vaporizes liquids and melts rocks. The pressure of these heated materials breaks the earth's crust, spraying the hot steamy materials into the air, and creating a volcanic eruption.

### LET'S EXPLORE

Do the types of surfaces rubbed together affect the amount of heat produced? Repeat the experiment, rubbing the eraser against different surfaces such as cardboard, a carpet, various cloth samples, and a wooden block. Be sure to use the same force and time for each material. NOTE: Since the eraser can remove color from surfaces, use small samples of materials that nobody wants. Science Fair Hint: The surface samples can be displayed, along with a small diagram of a thermometer noting the resulting temperatures.

### SHOW TIME!

1. Rice grains can be used to demonstrate that friction between rocks causes heat. Fill a quart (liter) jar with 1 cup (250 ml) of uncooked rice. Insert a thermometer. After one minute, read and record the temperature. Remove the thermometer, secure the lid on the jar, and shake it vigorously for 30 seconds. Immediately unscrew the cap, replace the thermometer, and measure the temperature of the rice.
2. Read about earthquakes and volcanoes. Make a list of the locations and names of volcanoes and areas with frequent earthquakes. On a globe or large world map, place labels with the letter E for earthquake areas and a V for the volcano locations. Compare the locations of earthquakes and volcanoes around the world to determine if there are more volcanoes in areas with greater crustal movement.

### CHECK IT OUT!

Volcanoes are located in two main regions on earth, called belts. One belt, called the Ring of Fire, circles the Pacific Ocean. The other belt is located along the shores of the Caribbean and Mediterranean seas. These belts outline where great crustal movement occurs. Find out more about the movement of the earth's crust by reading about the plate tectonics theory in earth science books.