Some fish and crustaceans adjust their density by accumulating low-density lipids or waxes. Students will compare and contrast these two means of achieving buoyancy, and understand why one doesn t work for the other. Notice what happens to the fish as air fills its swim bladder. Watch the level of water in the submarine s ballast tank as you squeeze and hold the bulb leading to the submarine. Observe the reaction of the submarine as water is pumped out of its ballast tank.
Density is mass divided by volume.
If the object s density is less than the surrounding fluid, the object will float. Fish are equipped with an air bladder inside their bodies. As the fish adds air to its swim bladder, it increases its volume. The fish s mass stays the same. Shrinking the swim bladder decreases the fish s volume.