## Floating Fish

Science Process Skills
• observing
• comparing and measuring
• inferring
• applying

Materials (per group)
• quarters
• foam packing peanuts
• small rubber band
• 16 oz. clear plastic cups
• tap water

Doing the Activity
1. See if the group can determine how something the weight of a quarter can swim so gracefully through the water. Give each group member a quarter, one foam packing peanut, rubber band, and a 16-ounce clear plastic cup filled with tap water.
2. Suggest to the group that the quarter represents the weight of a goldfish. Have them drop their quarter into the water and watch it sink. See if the group can guess how something the weight of a quarter can swim so gracefully in water.
3. Help the group understand that fish are able to swim through the use of a swim bladder. The foam packing peanut, like the swim bladder, contains air that helps the fish stay afloat. Challenge group members to make their quarter float.
4. Group members will need to attach a foam packing peanut to their quarter with a rubber band and observe how well it floats. Then have the group break off the right amount of foam packing peanut to make their quarter float beneath the surface of the water.
5. Help the group see the difficulties with too much or too little buoyancy.

Reflecting
• How did the amount of packing peanut influence the buoyancy of the quarter?
• What happened to the quarter if there was too much buoyancy? too little buoyancy?

Applying
How could you influence the buoyancy of the quarter by altering the water? Consider why some people say that it is easier to swim in sea water than fresh water.

What's Happening
Since the flesh and bones of fish are heavier than water, fish have air-filled sacs called swimbladders inside their bodies. The amount of air in the swimbladder is controlled by the fish. If air is added, either from the throat or oxygen from the blood the fish rises and if air is removed, the fish sinks.

More Challenges
• Alter the water by adding salt. Add 3 tablespoons of salt to your cup of water and stir until dissolved. Add the floating quarter and observe any changes.
• Would a saltwater fish need a larger or smaller swimbladder compared to freshwater fish the same size? (smaller)
• Would it be easier or more difficult for a saltwater fish to swim in salt water? (easier)
• If easier, how could the size or shape of saltwater fish differ from freshwater fishes? (larger and bulkier)

Activity Source
Robert Horton, Paul Speice, and Donna Manholt. "Fishy Science." The Ohio State University Extension, (614)292-1868, (order #10/93-5M-110641)

IOWA STATE UNIVERSITY
University Extension

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