Experiments to measure the upthrust of a liquid were first carried out by the Greek scientist Archimedes, who lived in the third century B.C The result of his work was a most important discovery which is now called Archimedes’ principle. In its most general form, this states:
When a body is wholly or partially immersed in a fluid it experiences an upthrust equal to the weight of the fluid displaced.
It should be noticed that the word “fluid” is used in the above statement. This word means either a liquid or a gas. The application of Archimedes’ principle to gases will be discussed later.