P=F/A whereas F is a vector... Pressure is the force act PERPENDICULARLY to a surface area. That's why I believe pressure is a vector quantity. And what I have read in Stress Tensor, Pressure should be a vector...
Most book say that P=lFl/A why lFl ???
So many things to clear up ... lets start here.
=>Pressure is the force act PERPENDICULARLY to a surface area
Think about a tire with air in it. Are all the molecules inside hitting the surface perpendicular? .... probably not hey the point Amit is making above.
So pressure is the CUMLATIVE PERPENDICULAR result of a series of smaller forces which are probably not perpendicular.
The result is perpendicular because that is the way we choose to measure it is probably not the direction of alot of the actual collissions.
Can you have a negative force? Answer no.
You either apply a force or you don't that is because we have Newtons first law ... remember a body with no force stays at rest. Hence no negative forces are possible ... what would a negative force even do ... make an unmoving body unmove more ????
So pressure can only be positive and it actually acts in all directions ... it's our containment into a vessel or virtual vessel (think magnetic confinement etc) and application of a surface area that creates a directionality but you still don't get positive and negative pressure.
What we are saying is pressure is scalar it's our measurement technique that makes it vector in nature.