The theory is that the water is acting as a lubricant.原理是水起到了润滑的作用

act as:担任, 充当

He was appointed to act as the executor.

他被指定为遗嘱执行人。

Maybe I can act as a messenger for you.

也许我能给你当信差。

To the naked eye, glaciers don't appear to move at all.肉眼看来冰川好像岿然不动

appear to:看来像是, 看来似乎

They appear to be able to handle the problem.

他们似乎可以处理这个问题。

The students appear to be completely out of hand.

学生们似乎已完全无法控制了。

at all:完全, 根本

It's not at all that bad.

这根本没有那么坏。

Whatever is worth doing at all is worth doing well.

任何值得做的事就值得做好。