A small triangular (wedge-shaped) element of a liquid lying in a horizontal plane is considered, with Pₓ, P_y and P_z being the pressures acting on its three faces. Which relation holds?

Pₓ = P_y not equal to P_z
Pₓ = P_y = P_z
Pₓ not equal to P_y not equal to P_z
Pₓ² + P_y² + P_z² = constant

Correct answer: Pₓ = P_y = P_z

Solution

For an infinitesimal fluid element, balancing forces on its faces (weight is negligible/out of plane for a horizontal element) shows the pressure is the same in every direction at a point.

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