What Is Buoyancy?
Both jars in this photo displace the same amount of water. But the jar on the right side is filled with lead, so the water it displaces weighs less than that jar. As a result, that jar sinks, while the jar on the left floats.
Archimedes Principle
A Greek philosopher named Archimedes studied the relationship between an object's buoyancy and the fluid it displaces. From his experiments, he concluded that "an object in a fluid is buoyed up by a force equal to the weight of the fluid it displaces." In simpler terms, this means that objects that are less dense than the fluid will float, and objects that are denser than the fluid will sink.
Imagine a bucket filled to the top with water. If you place a piece of foam on the water, a small amount will overflow from the bucket. This small amount of water weighs more than the piece of foam, which is why it floats.
Now imagine dropping a brick of lead in the bucket. The lead sinks to the bottom of the bucket and displaces more water than the foam. But this amount of water weighs less than the lead, which is why it sinks.
Imagine a bucket filled to the top with water. If you place a piece of foam on the water, a small amount will overflow from the bucket. This small amount of water weighs more than the piece of foam, which is why it floats.
Now imagine dropping a brick of lead in the bucket. The lead sinks to the bottom of the bucket and displaces more water than the foam. But this amount of water weighs less than the lead, which is why it sinks.
