So that means that N of P must be in magnitude the same as the frictional force.

这意味着PN必须,在大小上,与摩擦力相同。

You have already said in your book that "If you want to be effective in self-defence you must develop internal force and practise combat applications" (The Complete Book of Tai Chi Chuan, p. 64).

你门或许都在书里读过这样的话，“如果你想达到技击目的，你就必须练习内劲，并且实践格斗技巧“（太极拳大全，第64页）。

The average force vector quantities in all area were improved after training in the left hemiplegia and the healthy people(P<0.05).

正常人和左侧偏瘫患者各区力向量均值在训练后均有明显改善（P<0.05）。