Do the tangential force, the mormal force, the resultant force and their directions during oscillation of a simple pendulum change?

那么单摆在振动过程中，切向力、法向力及合力的大小和方向是否在变化?。

This paper suggests some general choice principles for the mormal equipment or products after analysis the quality standands of the industrial products.

通过对工业产品质量标准的分析，提出了杜绝“三无”产品，优选名牌产品，质量对比分析等一般的设备选择原则。