Sharks are pretty special. In addition to keeping ocean life in balance in their role as an apex predator, sharks are also great swimmers and most have fantastic night vision. Sharks also don’t have any bones – instead, they have cartilage, which is the same material that our ears are made of.
Today, we’re going to learn about how sharks swim and why they don’t sink to the bottom of the ocean (even though they can be very heavy!). Here’s what you’ll need:
Two plastic bottles with lids
A sink, bathtub, or large bowl
1. Fill one plastic bottle with vegetable oil, then put the lid on. Make sure it is secure.
2. Fill the other plastic bottle with water, then put the lid on. Make sure it is secure.
3. Fill your bowl, bathtub, or sink with about three inches of water.
4. Place both bottles into the water. Watch what happens. Which one sinks into the water? Which one floats closer to the top?
You should notice that the bottle with water will sink further into the water, while the bottle with oil floats closer to the top. That’s because oil is less dense than water. The tiny molecules in oil are farther apart, so the oil floats instead of sinks. If we had put something that was denser than water into the bottle, like honey, it would sink to the bottom.
What does this have to do with sharks?
Sharks have oil-filled livers that help them swim at different depths. Most fish have swim bladders, or pockets of gas, that help them swim and keep them from sinking. However, sharks can swim very deep in the ocean – so deep that if they had a swim bladder, it would burst from too much pressure! Instead, the oil in their liver helps keep them afloat, just like the oil in our bottle!
Predator: An animal that exists by eating other animals. Predators are very important because they help maintain balance in an ecosystem.
Apex Predator: An animal that exists by eating other animals and does not have any natural predators who would eat it.
Cartilage: Firm, flexible tissue.
Density: how tightly or loosely items are packed together.
For more animal science activities, visit the museum from now until August 15th!