Home >> Science & Nature >> Science

The Properties of Buoyancy

Buoyancy plays a large role in our interactions with water. Many people have an intuitiveness when it comes to determining which objects float and which objects sink. Knowing which objects are likely to sink or float depends on knowledge of an object's size and density. Some people, for example, may find it easy to float on the water. This feat is usually easier if someone takes in a large amount of air. With air in his lungs, a person can reduce the density of his body, making it more likely that he will float float.

Water Displacement
- When an object is placed in water, it displaces, or moves, an amount of water equal to its weight. For example, if you place a block of wood in a cup of water, the level of the water inside the cup will rise. If you measure the weight of the displaced water, it will be equal to the weight of the block of wood.
Density
- Although an object's size plays an important role in determining how much water it displaces, it is not the only factor. An object's density is a measure of how closely its molecules are packed together. Therefore, since metal is a denser material than wood, a metal block would displace more water than a wooden block, even if both blocks are the same size. However, when comparing two objects that are dense enough to sink, their level of water displacement is closely tied to their size.
Fluid Pressure
- As objects are submerged deeper and deeper, the pressure exerted by the water increases. The force of the pressure pushes in all directions. This fluid pressure holds aloft objects of a certain size and density. If an object is too heavy, it means its size and density exceed the force of fluid pressure that's pushing against it.
Sinking
- Objects that exceed a certain size and density sink to the water's bottom. However, if you handle a submerged object, its clear to see a difference in weight. Objects normally heavy outside water are less so when submerged in water. This occurrence is an effect of fluid pressure pushing up on an object. Although this force may not be enough to lift the object out of the water, it makes the object seem lighter to lift underwater.

Science