求翻译：若河床恰好为450斜面，它必受垂直重力和水平力双重作用而成流，可见，但凡水流皆受垂直与水平（二维）的力同时作用。是什么意思？

If the bed just as the 450 slope, it must be vertical and the horizontal force of gravity flow from the dual role, showing that, whenever water are subject to vertical and horizontal (2D) force simultaneously.

If river bed loft 450 happens, it will be for the vertical gravity and horizontal dual role, but become a river, it can be seen that where currents are subject to vertical and horizontal ( 2D) the power and role.

If the river bed is exactly 450 inclines, it must receive is vertical the gravity and the horizontal force dual function becomes the class, obviously, as long as the current of water all receives is vertical (two-dimensionally) with the level the strength also to affect.

If Riverbed exactly 450 incline, it is vertical and the horizontal force of gravity dual role and into a stream, can be seen, but where water is affected by vertical and horizontal (two-dimensional) force.

If the bed just as the 450 slope, it must be vertical and the horizontal force of gravity flow from the dual role, showing that, whenever water are subject to vertical and horizontal (2D) force simultaneously.