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Archimedes Principle

Archimedes principle states that a body that is totally or partially (not fully) immersed in a fluid (liquid or gas) will experience an upward force (upthrust) which is equal with the magnitude (size) and weight of the body, it displaces. 
The mathematical expression for Archimedes principle is given as:
$$F = v*g*(\rho_f - \rho_o)$$
where,
F = Buoyant force of the object in Newton (N)
V = volume of the object (m^3)
g = acceleration due to gravity = 9.80665 m/s^2}
$\rho_f$ = density of the object
$\rho_o$ = density of the fluid

Illustration:

From the above diagram, it is seen that when the stone is immersed in the liquid the volume of the water increases.
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