Sink or Float: The Weight of Water and You
 

	Fun Experiment to Try at Home!
		Purpose To determine how an object floats.   Materials - 12-inch-square (30-centimeter-square) piece of waxed paper - four small paper clips - 2-quart bowl - 12 pennies   Procedure 1.  Make a shallow box out of the waxed paper: Fold the paper in half four times to make a 3-inch (7.5-centimeter) square. * Fold up about 3/4 inch (1.7 centimeters) of each edge of the square to make the sides of the box. * Fold the paper to one side at each corner so that it is snug against the side of the box and secure it with a paper clip. 2. Fill the bowl about three-fourths full with water. 3. Set the box, open side up, on the surface of the water. Note how much of the box is above the surface of the water. 3. Count the coins as you place them in the box one at a time. Make an effort to distribute the coins evenly in the bottom of the box. Continue to add coins until the box sinks.   Sum It Up! Before any coins are added, the box floats with most of the box above the water line. With each addition of a coin, the box sinks lower into the water. When the weight of the box becomes more than the weight of the water the box can displace, the box sinks.

A naked scientist discovered how things float.
 
The Greek mathematician Archimedes was getting into a tub for a bath when he observed that the water spilled over the sides. He realized that there was a relationship between his weight and the amount of water displaced (pushed aside). He realized that the amount of water displaced (pushed aside) by his body was equal to the volume of his body. While floating in the tub, he also realized that all objects "lose" weight when placed in water.

Furthermore, the amount of weight an object apparently loses when placed in water is equal to the weight of the water the object displaces. He was so excited that it is said he ran naked through the streets yelling "Eureka!" His joy was because he had discovered a means of determining the densities of things based on their weight and weight loss in water. This technique was needed to determine whether the king's crown was made of pure gold. Archimedes discovered that the crown was not made of pure gold but was a mixture of gold and silver.

Archimedes experimented further and described what is now called Archimedes' Principle: a volume of water as heavy as a particular object must be displaced for the object to float.

For more information about floating (buoyancy), see "Janice VanCleave's 202 Oozing, Bubbling, Dripping & Bouncing Experiments" (New York: Wiley, 1996)