Buoyancy, or buoyant force, is based on Archimedes' Principle. This principle states, "Any object, wholly or partly immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object." Archimides' Principle is important in hydro-engineering applications, such as shipbuilding. The steps below detail how to calculate buoyant force.
- Skill level:
Things you need
Obtain the volume of the object on which you wish to calculate the bouyant force. We will call this value for the volume "V."
Determine what percentage (based on volume) of the object will be submerged in the water.
Convert this percentage to a decimal number. We will call this value "v." For example; if 100 per cent of the object is to be submerged, v= 1.0 . If 50 per cent of the object is to be submersed, v= 0.50 .
Substitute this value into the equation for buoyant force: FB = (V)(v) x (SPH2O) Where FB = buoyant force and SPH2O = Specific gravity of water (considered constant at 28.3kg per cubic foot).
Multiply V by v, and then multiply by 62.4 in order to get the value for the buoyant force, expressed in pounds. Consider the following example of a 2-foot by 2-foot by 2 foot cube to be submersed 25 per cent of the way in water. V = 222 = 8 cubic feet v = 25% = 0.25 SPH2O = 28.3 Kilogram per cubic foot FB = 8 *0.25 * 62.4 = 566 Kilogram
That's how you calculate buoyant force, and it helps illustrate how those large ships made of steel can float. That's quite a bit of force needed to push that 2 foot cube just one fourth of the way in the water!
Tips and warnings
- For laymen's calculations, the specific weight of water can be assumed to be 283 Kilogram per cubic foot, as this value does not vary significantly in normal temperature ranges.
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