what are two characteristics of fluids
1 1. Characteristics of a fluid Fluids are divided into liquids and gases. 2  A liquid is hard to compress and as in the ancient saying âWater takes the shape of the vessel containing itâ, it changes its shape according to the shape of its container with an upper free surface. Fig. 2.10 State change of perfect gas. 2  13. 3  18 Characteristics of a fluid The change in state of a perfect gas is expressed by the following equation: pv = constant where n is called the polytropic exponent. 4  As this value changes from 0 to 00, as shown in Fig.