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Floaters: How Can You Model the Position of an Iceberg in Water?

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Author: Janice VanCleave

Problem

How can you model the position of an iceberg in water?

Materials

  • 3-ounce (90-ml) paper cup
  • Tap water
  • Timer
  • Wide-mouthed quart (liter) jar
  • 2 teaspoons (10 ml) table salt
  • Spoon
    • NOTE: This project requires a freezer.

Procedure

Floaters

Floaters

  1. Fill the cup with water.
  2. Place the cup in the freezer for 2 hours or until the water in the cup is completely frozen.
  3. Fill the jar three-fourths full with water.
  4. Add the salt to the water in the jar and stir.
  5. Remove the ice from the cup. To do this, wrap your hands around the cup for 5 to 6 seconds. The warmth from your hands melts some of the ice, making it easy to remove.
  6. Tilt the jar and slowly slide the ice into the jar.
  7. Observe the amount of ice above and below the surface of the water.

Results

More ice is below the water's surface than above it.

Why?

When water freezes, it expands. The density of ice is slightly less than the density of water. As a result, ice floats in water, but is only slightly lifted above the water's surface. The greater the difference between the density of water and the density of ice, the higher the ice floats in the water. Icebergs (large mass of floating ice in the ocean), like the ice in this experiment, float in seawater, which is salty. Icebergs would float slightly lower in freshwater because the difference in density between ice and freshwater is less than that between ice and seawater.

Let's Explore

Arctic icebergs are generally jagged pieces of ice. How does this irregular shape affect the position of the iceberg in the water? Repeat the experiment, making two cups of ice. Remove the ice from the cups, and place the two pieces on a plate. Wet 2 to 3 ice cubes with water and stack them on one of the blocks of ice. Put the plate back in the freezer for 10 minutes. Place the ice pieces into a large see-through bowl filled about threefourths full with water. Compare the amount of ice each block has above and below the water's surface.

Show Time!

Fill the foil box with water and set it on a plate. Place the plate in the freezer for 3 hours, or until the water in the box is completely frozen. Fill a 2-quart (2-liter) transparent bowl three-fourths full with water; add 1 tablespoon (15 ml) of table salt and stir. Remove the ice from the foil box by peeling away the foil. Place the ice in the bowl, and observe the amount of ice above and below the surface of the water.

Floaters

  1. Antarctic icebergs are tabular (table top) in shape. Make a model of a tabular iceberg by forming a rectangular mold from a 12-by-18-inch (30-by-45-cm) piece of heavyduty aluminum foil. Make a shallow box out of the piece of foil by following these steps:
    • Fold the foil in half three times to make a 41/2-by-6-inch (11.25-by-15-cm) rectangle.
    • Fold up about 1 inch (2.5 cm) on each edge of the foil rectangle to make the sides of the box.
    • Fold each corner of the foil to one side so that it is snug against the sides of the box.
  2.  
    1. The color of the ice in icebergs depends on the materials trapped inside the ice and how compressed the ice is. Trapped air bubbles tend to reflect more light, causing the ice to look milky white. Design a way to freeze water with different amounts of air bubbles. The warmer the water, the less gas dissolved in it. Try freezing both warm and cold water. Fill one 3-ounce (90-ml) paper cup with warm water and a second cup with cold water. After the water freezes, compare the color of the two ice samples.
    2. Another possible way to increase the amount of air bubbles might be to mix the water with air. Repeat the previous experiment, but pour the cold water into a jar. Seal the jar and shake it vigorously to mix the water and air inside. Then, pour the water into the paper cup for freezing. Again, compare the color of the frozen samples. For more information about the color of icebergs, see pages 158–159 in Janice VanCleave's Oceans for Every Kid (New York: Wiley, 1996).

Check It Out!

Some Arctic icebergs are as large as a 10-story building. But not all bergs are kingsize; some are small. Those measuring up to about 33 feet (10 m) across are called growlers. Find out more about icebergs. What are bergy bits? How does the size of Arctic and Antarctic icebergs compare? How are icebergs formed? Where are most of the icebergs formed? For information, see ice and ice formation in an encyclopedia.

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