The sink or swim experiment is an effective method of teaching the principles of buoyancy. Gather several items that vary in weight and size: items such as clear, empty water bottles; ping pong balls; golf balls; rocks; and large and small pieces of wood. Add water to a bucket or other open container. Do not completely fill the container to avoid spilling any displaced water. Put the empty water bottle in the water and observe its effect on the water level. Fill the bottle with sand and place it in the water. Observe the effect when the density of the bottle has increased. Do the same for the other objects.
This experiment demonstrates how an increase in the density of an object decreases the object's buoyancy. You will need a ruler, seven pennies and some aluminum foil. Add water to a bucket. Do not completely fill the container with water. Make a boat out of aluminum foil, place it in the container and, with the ruler, measure the distance between the bottom of the container and the bottom of the boat. Place pennies in the boat, one at a time, and measure the boat again after each penny has been added. Observe and record your results.
This experiment demonstrates how objects, affected by outside forces, become buoyant despite their density in relation to the fluid they occupy. Place seven raisins in a glass of clear soda and make sure to notice that the raisins initially sink to the bottom of the glass. The bubbles of the carbon dioxide will gather around the raisins and bring them to the surface again. The bubbles will burst and the raisins will sink to the bottom of the glass again. This will continue until the carbon dioxide in the glass has been depleted or the raisins have absorbed too much fluid.
A unique quality of water is that, when frozen, it has a lower density than when it is in a fluid state. When water freezes the molecules spread apart from each other, causing a decrease in density. Find the density of a small volume of water; freeze the same volume of water and determine if the density remains constant.