ok so my friend told me that in a container, the pressure exerted by the walls on the liquid in the container act in the upward direction.Is he correct ? so what I am imagining is a cylindrical container kept on the ground. according to me the pressure by the wall of the container should act perpendicular to the surface of the wall.Am i going wrong somewhere ? Any help would be appreciated.
Answer
Pressure at a point in a static fluid is independent of direction.
The force exerted by the walls on the liquid will be pointing inwards. Imagine if there is a hole in the container and water is liquid out, it is easy to see that you have to apply a force inwards in order to prevent the liquid from leaking. Since the force is proportional to the area of the hole, you'd want a dimensionally equivalent form of pressure in order to eliminate the dependence on area. And that is stress. (Note that stress is not a scalar nor a vector - it is a tensor)
http://en.wikipedia.org/wiki/Stress_(mechanics)
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