moved the definition of fluid to its article
'''Fluid mechanics''' is the study of the motion of
fluids and the forces that leads to these motions. It can be further classified into two categories: [[fluid statics]] (studies of fluids at rest) and [[fluid dynamics]] (studies of fluids in motion) . The "fluid" in the term fluid mechanics is defined<ref>James R. Welty, Charles E. Wicks, Robert E. Wilson, and Gregory L. Rorrer, Fundamentals of Momentum, Heat, and Mass Transfer, 4th Ed. Toronto: John Wiley & Sons Inc, 2001.</ref> to be "a substance which deforms continuously under the action of a shear stress", which includes both liquids and gases.