Floating ice
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Materials needed:
Clean plastic container (such as large margarine tub)
Refrigerator freezer
Water
Sink
Ruler
Towel
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Icebergs are large pieces of ice that have broken off from glaciers or polar ice sheets. Composed mostly of frozen freshwater rather than frozen seawater, icebergs can float many years in the ocean before completely melting. In this experiment you are going to make a large piece of ice and use it to learn more about icebergs.

Fill a clean plastic container three-quarters full with water. Place the plastic container of water in a freezer and leave it there until all the water has frozen (overnight is long enough).

Remove the container of frozen water from the freezer and place it on the kitchen counter. Fill the sink nearly full with water. Remove the large piece of ice from the container. If the ice does not slip out easily, place the container in the sink of water and leave it there until the large piece of ice is loose.

Place the large piece of ice in the water. Does it sink or float? Use a ruler to measure the height of the ice sticking above the surface of the water, as shown in. Next, remove the ice from the water and place it on a towel next to the sink with the same side on top as when it was floating. Now measure the total thickness of the ice.

To calculate the percentage of ice that is submerged (below the surface of the water), first divide the height of the ice that is above the surface of the water by the total thickness of the ice. Multiply this number by 100 to get the percentage of ice floating above the surface of the water. Subtracting this percentage from 100 gives you the percentage of ice submerged. For example, if 0.8 in. (2 cm) of ice is floating above the surface of the water and the total thickness of the ice is 7.9 in. (20 cm), then 10% (0.8 / 7.9 x 100% = 10%) of the ice is floating above the surface of the water and 90% (100% - 10% = 90%) of the ice is below the surface.

Water is an unusual substance because solid water (ice) has a lower density than liquid water. For most substances, the liquid form is less dense than the solid form. Density is the ratio of the amount of a substance (mass) to the amount of space (volume) taken up by the substance. To help clarify, imagine you have 1 cup (0.24 l) each of two different liquids. Let's call them liquid A and liquid B. if liquid A has a greater density (is more dense) than liquid B, then the cup of liquid A will weigh more (have a greater mass) than that of liquid B. To think of it in another way, say you have separate samples of liquid A and liquid B that have the same weight. If liquid A is denser than liquid B, then liquid A will have a smaller volume.

A less dense substance will float on a denser substance. This is why ice floats on water. For nearly every other substance, the solid form will sink in the liquid form.

In this experiment you should find that 80% to 90% of your piece of ice is submerged. This percentage will vary depending on the amount of air trapped in the ice. The more air that is trapped, the less dense the ice and the smaller the percentage that is submerged. Ice made from water containing no air is 90% submerged in pure water.