Fluid

In fluid dynamics, a fluid is a substance that continually deforms under an applied shear stress. Fluids have zero shear modulus, meaning they cannot resist any shear forces applied to them. The term fluid generally includes both liquids and gases, but its definition varies among different fields of science. In some cases, substances can exhibit both fluid and solid properties, such as non-Newtonian fluids like Silly Putty or viscosity substances like pitch. In particle physics, the concept of fluids extends beyond just liquids and gases. In medicine and biology, fluids refer to any liquid constituent of the body, while in hydraulics, fluids are liquids with specific properties.