关于流体力学中的无滑移条件1：When fluid is next to a solid surface,there i

关于流体力学中的无滑移条件
1：When fluid is next to a solid surface,there is no slip of the fluid relative to the surface (i.e.the fluid that touches the solid surface does not move relative to it).
2：
If the surface is stationary,then the fluid immediately adjacent to the surface must have zero velocity.
3：
Fluid any distance from the surface can move – there can therefore be relative movement between different parts of the fluid Þ shear stress is created if the fluid has viscosity
这是我们上课的PPT资料,个人有点不能理解,觉得第一条和第二条有点矛盾,第一条是说流体在经过固体表面时并不过与固体表面有相对的运动.但是第二条又说如果这个固体表面是静止的,那么与固体表面相邻的流体一定没有速度.有点不能理解,（我也查过一些资料,但是不能理解什么叫法向和切向,所以还是看不懂,感激不尽啦）