How to Calculate Buoy Floatation in the Water

Buoys float because their density is less than that of water
••• Thinkstock/Comstock/Getty Images

Buoys, balloons and ships are familiar examples of items that float. The phenomenon of flotation, however, is not commonly understood. Flotation was first explained by the classical Greek mathematician, Archimedes, who formulated the famous principle that bears his name. Archimedes' Principle states that an object completely or partially immersed in a fluid (a liquid or gas) is acted upon by an upward, or buoyant, force equal to the weight of the displaced fluid. Buoyant force arises from a difference of density between a fluid and an object immersed in the fluid.

    Imagine a buoy made of cork floating on water. Assume that the buoy has a volume of 2 cubic feet (ft-cubed) and a density of 15 pounds per ft-cubed. Calculate the weight of the buoy as follows: 2 ft-cubed x 15 pounds / ft-cubed = 30 pounds.

    Calculate the weight of water that has a volume equal to that of the buoy, using 62.4 pounds / ft-cubed as the density of water, as follows: 2 ft-cubed x 62.4 lbs / ft-cubed = 124.8 pounds / ft-cubed.

    Note that the buoy, if held under water, displaces 124.8 pounds of water. According to Archimedes' principle, the buoyant force acting on the cork is 124.8 pounds, which is greater than the weight of the cork. Therefore, if the cork is released the buoyant force pushes it to the surface, where it remains partially immersed.

    Calculate the volume of water displaced by the floating buoy, as follows: 30 pounds of water / [62.4 pounds / ft-cubed] = 0.481 ft-cubed.

    Calculate the amount of the buoy's volume remaining above the surface of the water, as follows: 2 – 0.481 = 1.519 ft-cubed. The percentage of the buoy's volume above water is therefore: [1.519 / 2] x 100 = 76 percent.

    Tips

    • The density of water is 62.40 pounds / ft-cubed at 26 degrees Fahrenheit, the temperature of cold sea water. The density of water, like that of any fluid, decreases with increasing temperature. For example, the density of water is 62.30 pounds / ft-cubed at 70 degrees Fahrenheit. The most accurate measurements involving density are obtained by using values at specific temperatures.

Related Articles

How to Tell if an Object Will Sink or Float
How to Calculate Buoyant Force
Difference Between Density & Mass
Volume Vs. Mass Density
How to Calculate Sphere Size
How to Calculate The Underwater Volume
Gallons to Kilograms Conversion
Brine Vs. Conductivity
How to Convert Fluid Ounces of Water to Weight
How to Calculate Wind Load on a Large Flat Surface
How do I Convert M3 into Kilograms?
How to Calculate Tons
How to Convert UG/mL to PPM
How to Calculate Solubilities
What Is the Density of CO2?
How to Convert Milligrams to Fluid Ounces
Why Rubber Floats in Water
How to Dissolve Sodium Bicarbonate
How to Calculate Hydraulic Cylinder Tonnage