friction这个词有好几个定义和用法，多数情况下是不可数名词，但如果用作描述人际或国际关系的摩擦和冲突，就做作可数名词用了。请看例句：
1 [uncountable] the action of one object or surface moving against another
Friction between moving parts had caused the engine to overheat.
2 [uncountable] (physics) the resistance (= the force that stops something moving) of one surface to another surface or substance moving over or through it
The force of friction slows the spacecraft down as it re-enters the earth's atmosphere.
3 [uncountable, countable]
friction (between A and B)
disagreement or a lack of friendship among people who have different opinions about something
synonym tension
conflicts and frictions that have still to be resolved
参考资料：Oxford Advance Learner's Dictionary