Real and ideal liquids

An ideal liquid is treated as a continuous medium the molecular structure of the real liquid is ignored. 

There are no tangential stresses in the ideal liquid, even when flow takes place. Therefore, under all conditions, the pressure at any point in an ideal liquid is independent of direction and the coefficient of viscosity is zero. 

If there is a rigid body in the ideal liquid the normal relative velocity is zero always, that is, the ideal liquid slips over the surface. For real liquids there is, in fact, no slip at the surface. 

As a further simplification an ideal liquid is often assumed to be incompressible, but this is not an essential condition. 

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