Archimedes studied the upthrust acting on a body, when it is completely or partially immersed in a fluid by performing several experiments and then started the following principle known as Archimedes principle.
When a body is partially or wholly immersed in a fluid, it experiences an upthrust equal to the weight of the liquid displaced.
- Take a piece of stone and tie it to one end of a rubber string or a spring balance.
- Suspend the stone by holding the balance or the string as shown in Fig. a
- Note the elongation of the string or the reading on the spring balance due to the weight of the stone.
- Now, slowly dip the stone in the water in a container as shown in Fig. b
- What you will observe is that the elongation of the string & the reading of the balance decreases as the stone is gradually dipped into the water.
- Since the extension decreases once the stone is lowered in water, it means that some force acts on the stone in upward direction. As a result, the net force on the string decreases and hence the elongation also decreases.
Applications of Archimedes principle:
- It is used in designing ships and submarines.
- The lactometers and hydrometers used for measuring the purity of a sample of milk and for determining the density of the liquids are based on the principle.
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With the use of Archimedes' principle, state how you will find relative density of a solid denser than water and insoluble in it. How will you modify your experiments if the solid is soluble in water?