About Bouyancy

Have you ever wondered why some things float and some things don’t? Ever asked why there are huge icebergs in the middle of the frozen sea that float? Have you wanted to know why your cookie comes back to the top if you drop it in your milk? Well you’ve come to the right place. Buoyancy is the force that causes all of these things to happen and here are some things that you need to know about buoyancy.

In the world of physical science, buoyancy is the upward force exerted on an object that is a result of the surrounding fluid, which can be either a liquid or a gas. This is true whether the object is completely or only partially immersed in the fluid and this force is caused by the difference in pressure of the fluid at the top and bottom of the object in it. The force of buoyancy allows the object to float or at least to seem lighter while it is in the fluid. The total of the upward force exerted on the object equals the total weight of the fluid that is displaced by the presence of the object in it (more on this later). This force becomes very important in navigating the oceans and the skies and things like boats and balloons are secretly showing us the force of buoyancy at work.

As mentioned before, buoyancy exerts and upward force on the object in the fluid. The strength of this force is the same as the weight of the displaced fluid. The concept of displacement is the word used to describe this and is often used to replace or mean the same thing as buoyancy. So the buoyancy of an object depends on two things; the volume of the submerged object and the density of the surrounding fluid. The higher the volume of the object itself and the higher the density of the surrounding fluid the more buoyant force is experienced by the object. If the buoyancy of the object in a particular fluid is greater than the weight of the object, it will float; if it is less then the object will tend to sink.

The concept of buoyancy is based on the idea of Archimedes’ principle. This principle says that “When a solid body is partially or completely submerged in water the apparent loss in weight will be equal to the weight of the displaced liquid. Archimedes of Syracuse discovered this law of nature while in the bath. This is something you may have noticed in a bathtub as well. When the tub is full and you get into the water, the level of the water rises. If you could weight the water that was displaced, it would be exactly equal to the weight of the part of your body that was underwater. The same would be true no matter what type of liquid it was; it could be jell-o, chocolate syrup or even air. The weight of the displaced fluid always equals the weight of the object displacing it.

Another interesting thing about buoyancy is that is makes things seem lighter when they are completely immersed in a fluid. The buoyant force can be subtracted from the actual weight of the object while it is underwater. The buoyant force makes the object feel lighter. You have probably noticed that objects are easier to pick up while they are underwater. They seem to be lighter because of the buoyant forces that are acting upon them. Large objects, like sunken ships, are easier to lift underwater than they are on land because of buoyancy.
This is also the reason that astronauts train underwater. It gives them the sense of feeling lighter, a feeling that is also experienced in space because the forces of gravity aren’t acting on them. Buoyancy is a very important concept in our lives whether we realize it or not.


Cite This Page

Feldman, Barbara. "About Bouyancy." Surfnetkids. Feldman Publishing. 24 Mar. 2008. Web. 3 Sep. 2014. <http://www.surfnetkids.com/go/137/about-bouyancy/ >.

Learn more with these Bouyancy websites.



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