Question
Show that the force acting on the liquid in equilibrium is perpendicular to the free surface of liquid.
Solution
Consider a liquid in a container. The liquid is in an equilibrium condition. Force F is acting on the liquid at angle with the free surface of liquid as shown in figure below.
On resolving the components of force, we get
Fcos - component of force along the surface
Fsin - component of force ormal to the surface
In the equilibrium state, component of force along the surface is 0.
Therefore,
Fcos = 0
On resolving the components of force, we get
Fcos - component of force along the surface
Fsin - component of force ormal to the surface
In the equilibrium state, component of force along the surface is 0.
Therefore,
Fcos = 0
So, the force must be normal to surface.
Thus, the free surface of liquid in equilibrium adjusts normal to the direction of force acting on it.
