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Break Away: How are Coins Affected by Routine Handling?

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Author: Janice VanCleave

Problem

How are coins affected by routine handling?

Materials

  • sheet of typing paper
  • desk lamp
  • 5 used pennies
  • 5 new pennies
  • magnifying lens

Procedure

  1. Place the sheet of typing paper on a table under the lamplight or near a window.
  2. Place 5 used pennies and 5 new pennies on the paper so that the image of the Lincoln Memorial faces up.
  3. Use the magnifying lens to observe any differences in the image on the used and new coins.
  4. Break Away

    Break Away

  5. With your unaided eye, look at the center of the Lincoln Memorial on each coin.
  6. Now use a magnifying lens to look at the center of the Lincoln Memorial on each coin, and note any difference.

Results

The image on the new pennies is sharper and easier to see. The image on the used pennies looks smoother, and on some coins small details are not visible. All the coins have a raised area, but it is difficult to identify the object with the unaided eye. With a magnifying lens, you can see a sharp image of Abraham Lincoln sitting inside the building. The same image of the man is visible on the used coins, but is much less clear.

Why?

The image on each coin is changed by a process called erosion. Erosion is the loosening and eventual wearing away of particles that make up an object. Every time a coin is touched, small particles of metal on its surface are moved slightly. After enough handling, metal pieces break away. In time, the surface of each coin becomes smooth. This same process occurs on rocks, buildings, statues, and other objects that are touched by wind, water, or human hands.

Try It With A Microscope

Microscope Procedure

  1. Lay one of the pennies on a microscope slide.
  2. Position the desk lamp so that the coin is brightly lit from above.
  3. Under the low-power objective of a microscope, study the surface of the coin, Lincoln Memorial side up.
  4. Move the coin around to observe its surface.
  5. Study the surfaces of several used and new coins.

Microscope Results

Specks of dirt and corrosion not visible with the naked eye or magnifying lens can be observed on the coins. Science Fair Hint: Drawings of the microscopic views can be made and displayed to represent the degree of erosion on used and new coins.

Let's Explore

Does the metal on all coins erode from handling? Pennies are made of copper. Repeat the original experiment using coins made of different metals, such as nickel. If possible, observe coins from different countries. Science Fair Hint: A collection of the different coins used in the experiment can be used as part of a project display.

Show Time!

How do chemicals affect metallic surfaces? Show the effect of acid on coins made from copper by placing a folded paper towel in a saucer. Pour enough vinegar into the saucer to wet the towel and place five or more new pennies on top. After 24 hours, observe the surface of the coins as in previous experiments with a magnifying lens and a microscope. Check with a chemistry teacher for information about the chemical reaction between vinegar and copper that produced the green coating, or see "Green Pennies," page 92 in Chemistry For Every Kid, (New York: Wiley, 1989), by Janice Van-Cleave. Before-and-after photographs taken of the coins, along with diagrams and descriptions of the observations, can be displayed.

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