Children can learn about the ways in which underwater vessels work in order to gain basic knowledge about buoyancy and pressure. To start, an adult should pierce a few holes, the diameter of a pencil, into the side of a plastic bottle. A kid can then tape a few coins near (but not on) the bottle to function as weights. Plastic tubing is placed inside the bottle. It is sealed shut with modeling clay, then placed into a bucket of water. As children blow into the bottle via the tubing, it rises and falls in the water. The air from their breath forces water in and out, changing the air pressure and the bottle's buoyancy.
The Cartesian diver experiment is a classic that teaches basic facts about buoyancy. The use of a small ketchup packet lends an informal nature to the experiment that can help draw in young learners. A student first removes labels from a plastic bottle, then fills it to the brim with water. She then inserts the ketchup pack. If the packet sinks, she can add tablespoons of salt to the water, a few at a time, shaking the bottle to dissolve the salt. When she squeezes the bottle, the pack should sink, and vice versa when releasing her grip.
Balloons, well known for their buoyancy and ease of floating, can be used for lessons on air pressure as well. Securing two 1-liter soda bottles, one of them should be punctured through with a small nail 5 cm from its bottom. An empty balloon goes into each bottle, its opening stretched over the bottle's both. Students attempt to inflate both balloons by blowing into them. They should try to do this repeatedly using several variables, like holding a finger over the hole or the bottle's mouth or filling it with water.
An egg, a glass, water and salt can expose students to the differences between saltwater and fresh water in terms of buoyancy. The experiment begins by placing the egg in the glass, then filling it with water. The egg should rest at the bottom of the glass; an old egg will float, and is not suitable for this process. A student then removes the egg from the glass with a spoon. Next, he pours enough salt into the glass, little by little, so that it no longer dissolves in the water. Returning the egg to the glass, he should notice that it floats.