Cucumber Canoes Pennsylvania Academic Standards: Science 3.4.7.D Unfortunately, you wouldn't make it very far if you tried to ride a cucumber canoe down the river. However, a ride in a real canoe can be great fun. Have you ever wondered why canoes float? Here is a little experiment that you can do with materials you probably already have in your kitchen. You will be looking at both density and buoyancy. Density is the weight of an object compared to its volume or how compact an object is. Buoyancy is the upward force on an object in a fluid. Follow the instructions for the experiment and then see if you can answer the question: Why do canoes float? Materials: 1 fresh egg 2 tall clear drinking glasses Water Salt, up to 1 cup A spoon Experiment: Fill one glass with water. Place the egg in the water and observe what happens. Does the egg float or sink? Now place at least one inch of salt in the other glass and fill it with water. Stir in the salt so it dissolves. Place the same egg in the glass of salt water and observe what happens. Does the egg float or sink? What happened? Density determines what will float and what will sink. More dense substances sink in less dense liquids. A fresh egg is a little denser than plain water so it sinks. When salt is added to water, particles of salt move in between water particles, making the salt water denser. The salt water is a little denser than the egg, so in salt water, the egg floats. So, you still may be wondering why density differences determine what floats or what sinks? This is where the buoyant force comes in! A force is a push or pull. Water will exert an upward force on objects (like the egg or your canoe) that are put into it because water pressure increases with depth. The Archimedes' Principle says that the strength of the buoyant force is equal to the weight of the water that was moved out of the way by the object. Boats are shaped to displace a lot of water in order to have enough buoyant force exerted on them by the water to float. The canoe you ride in has enough buoyant force to stay afloat because of its shape. Think about the gigantic cruise ships in the ocean-now that's a lot of buoyancy! The next time you are crunching away on a Cucumber Canoe and the question of how a boat floats comes up; you can quote the Archimedes' Principle and really impress your friends. You just might teach them something too! Experiment and information was adapted from: Flash!, Bang! Pop! Fizz! Exciting Science for Curious Minds by Janet Parks Chahrour, copy right 2000 by Barron's Educational Series, Inc.
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