Both stress and pressure are force per unit area.So, what's the difference b\w them?

Asked by keerthi b | 29th Nov, 2010, 12:00: AM

Expert Answer:

Like force and velocity, stress is a vector quantity. The stress vector can be resolved into a component perpendicular to the surface (the normal stress), and a component parallel to the surface (the tangential, or shear stress).
The stress field about any point in the body may be isotropic (also called hydrostatic) or anisotropic (non-hydrostatic). If we imagine a simple, infinitesimal cube, with its sides oriented orthogonally to the three cartesian coordinates, we can define a normal stress, S1, S2, S3 perpendicular to each pair of sides of the cube. These stresses are defined so that S1>S2>S3. Note that stress has units of Pascals = N/m², (where N = newton). The Pascal is the SI unit of pressure.

Pressure

When the stress field is hydrostatic, S1=S2=S3 = P, where P = pressure. Pressure is a scalar (non-directional) quantity; stress is directional. Only when the stress field is isotropic does a thermodynamic pressure exist.

Answered by  | 30th Nov, 2010, 01:17: AM

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