We are nearing the end of learning to care for goldfish. We need a new subject to learn. The first kid that emails me can select the next exotic pet to discover together. If you click my name, Diana Geiger you will see a place to put your email and your message. Plus, feel free to email me anytime I will be glad to answer your questions.
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Fun experiments; did you remember the plastic soda bottle you were supposed to find and save? Either you can do this experiment in the bathtub while taking a bath or in a sink. Be careful we don’t make a mess and get water on the floor. Please ask your parents’ permission to do this experiment.
You are going to learn how a fish can rise to the surface of his tank, or go all the way to the bottom of the tank. This is called buoyancy. First of all take the empty bottle with the lid on and set it in the water. What do you see happening? Does the bottle sink to the bottom or does it float on top? You’re right it floats on the surface of the water. That is because the bottle is filled with nothing but air.
Fish have something called a swim bladder. The swim bladder works pretty much just like the bottle you are experimenting with now. Now fill it completely full with water and attach the lid. Now what happens? It sinks to the bottom of the tub or sink. Now dump one third of the water out of the bottle and replace the lid. What happens now? It has air and water in the bottle. Like a fish’s swim bladder which also can be regulated to hold different amounts of air.
The bottles with two-thirds water doesn’t sink to the bottom, nor does is rise to the surface. It will linger between the bottom and the centerline of where the water reaches the tub.
Now dump more water out of the bottle, leaving about one-third of the water left in the bottle. What happens now? It should be somewhere between the top of the water and centerline. Now you know how a fish can swim to the top of the water and swim back down to the bottom of his tank, or anywhere in-between. They control their depth much like a submarine does, using buoyancy. They take in more air to rise closer to the surface. If he wants to swim to the bottom of the tank he will let air out of this swim bladder to make him less buoyant.
Now just for the fun of it place your hand in the water with your hand straight out. Gently move your fingers back and forth (like a wave motion with your fingers close together.) Do you feel the water move around your hand? This is how the fish propels himself with his tail. Wiggle your hand back and forth and that would be like a fish’s tail moving the fish through the water. The fish use their fins to control turns.