I love watching penguins! Their secret is that they fly. Okay, so they dont soar through the sky like other birds, but they do fly underwater, and can get enough power to pop out of the water. The larger the wing, the more power the penguin can create. Some species leap out of the water as they swim. This is called porpoising.

Penguins do not have swim bladders like some fish do. Penguins dive to find their food, so they are better off not floating. Their skeletons are much heavier than the skeletons of flying birds that are the same size. This allows them to dive.

Swim bladders help a fish float in water because the air in the swim bladder is less dense than water. Less dense things float on more dense things. Density means how much stuff is packed into a space. Think about a sponge or a marshmallow. If you squish it down, it has the same amount of stuff (matter) but it takes up less space (volume), so it has a higher density when it is squished. An unsquished marshmallow floats on water because it is less dense than water. Would a squished marshmallow still float? Now theres an experiment Id like to do right now with some hot chocolate!

Sharks dont actually have a gas-filled air bladder, but they do have a big oily liver. We all know that oil floats on water, so we know that its less dense than water. Neither of these floatation devices is less dense than air, so they would not help once the fish left the water.

SeaWorld has a nice site on penguin swimming: SeaWorld