Stress and Pressure?

Question

Why stress and pressure are considered to be two different physical quantites thogh they have same formula.

Answer 1

Stress relates to internal stressing of a structure, to bend it, compress or stretch it. They are internal to the structure and will change with changes to the structures properties/shape.

Pressure would be more like a distributed load being applied to the structure. For example a pressurized vessel (or container) puts a load onto wall structure of the vessel.

Answer 2

Stress is a more general concept than pressure. Pressure is istrotropic stress. That means the force per unit area is the same in all directions and results in uniform compression. In addition to this, solid material (with structural strength) can have deviatoric stress too, like tension and shear. That means that both the direction and magnitude of the force per unit area depend on direction. Think of a rope. It has tensile stress only in one direction when loaded. To place it under pressure, though, you can submerge it underwater.

Answer 3

Not clear they are considered different physical properties. I certainly don't consider them to be different. They are both F/A...force over an area. That's pressure.

Stress is pressure. But, typically, we call it stress when related to strength of materials. But that's just a matter of convention.