The concept of a fluid A solid can resist a shear stress(剪切应力) by a static deformation a fluid can not Any shear stress applied to a fluid, no matter how small, will result in motion of that fluid The fluid moves and deforms continuously as long as the shear is applied 2021/2/222021/2/22 3 The concept of a fluid A solid can resist a shear stress(剪切应力) by a static deformation, a fluid can not. Any shear stress applied to a fluid, no matter how small, will result in motion of that fluid. The fluid moves and deforms continuously as long as the shear is applied