•    Consider a tank felled with liquid moves towards the right side with a uniform acceleration.

•    As the tank stats moving under the action of acceleration force, the liquid does not remain in horizontal level.

•    The liquid surface falls down on the direction of motion and rise up on the back side of the lank.

•    Consider the equilibrium of a fluid particle A lying on the inclined free surface as shown in.

The force acting on the liquid particle are weight of the particle W = mg acting vertically downwards, accelerating force F acting toward right and normal pressure P exerted by the liquid.

Acceleration force F = ma

Resolving horizontally P sin θ = F = ma

Resolving vertically P cos θ = W = mg

Dividing Equation (i) to (ii)

P sin θ / P cos θ = ma / mg = a/g

tan θ = a/g

Now consider the equilibrium of the entire mass of the liquid. Let P₁ and P₂ are the hydrostatic pressure on the back side and front side of the tank.

Net force P = P₁- P₂

By Newton’s second law of motion,

P = ma

(P₁-P₂) = ma

•    Since the inclination θ of liquid surface remains constant all the points on the liquid surface, therefore the liquid surface will be inclined at a constant angle θ with the horizontal.

•    The inclination of the liquid surface is directly proportional to the horizontal acceleration.

•    The fuel tank on an airplane during take-off is the best example.

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