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How Fish Sink and Float

Active Time
45 minutes to 1 hour
Total Project Time
45 minutes to 1 hour
Key Concepts
Physics, Buoyancy, Archimedes Principle
How Fish Sink and Float - Science Activity

Introduction

Have you ever thought about why most fish never sink to the bottom of the ocean or float to the water's surface? How is it that they can stay so perfectly buoyant under water? You might be surprised to hear that most bony fish have a special organ to help them with that: a swim bladder. The swim bladder is a thin-walled sac located inside the body of the fish that is usually filled with gas. Besides helping the fish stay buoyant, it can also function as a sound producer and receptor or as an accessory respiratory organ. Wonder how a swim bladder works? Then do this activity to find out!

Credits

Svenja Lohner, PhD, Science Buddies
This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,150 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.

Materials

  • Small glass bottle
  • Balloon that fits inside the bottle
  • Plastic tubing (at least 30 cm or 12 inches)
  • Big tub or container, waterproof and preferably transparent. It should have enough room so the glass bottle can float in it freely.
  • Strong and waterproof tape
  • Water
  • (Paper) towels
    Materials you need to make your swim bladder model

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Active Time
45 minutes to 1 hour
Total Project Time
45 minutes to 1 hour
Key Concepts
Physics, Buoyancy, Archimedes Principle