"When the weight of a body is equal to the weight of liquid displaced by the part of the body immerged in it, the body floats on the surface of the liquid."

For example : Boat, Steamer.

When a body is partially or completely immerged in a liquid, it experiences two forces.

$(1)$ Weight of the body $\mathrm{W}=m g$

$=\rho_{f} V_{s} g($ in downward $)$

Where $m=$ volume $\times$ density $\left(\mathrm{V}_{s} \rho_{s}\right)$ and $\mathrm{V}_{s}=$ volume of body, $\rho_{s}=$ density of body.

$(2)$ Buoyant force of body,

$\mathrm{F}_{b}=$ weight of displaced liquid

$=\rho_{f} V_{s} g$ (in upward direction)

where $V_{f}=$ volume of displaced liquid,

$\rho_{f}=$ Density of liquid

Cases:

$(a)$ If $\mathrm{W}>\mathrm{F}_{b}$, the body sinks.

Example : Piece of iron

$(b)$ If $\mathrm{W}=\mathrm{F}_{b}$, the body remains in equilibrium at any depth.

Example : Submarine.

$(c)$ If $\mathrm{W}<\mathrm{F}_{b}$ the body floats on the surface of the liquid.

For example : Submarine, boat