EARTHLY POWERS (ANTHONY BURGESS) AND INERTIA

We were all still standing up, but now Carlo sat down. The whisky in his glass tried to stay where it was and splashed his black jacket. He ignored this, looking, frowning, up at his brother.

I wrote inertia, but, which is the real cause of the whisky falling? Is it maybe because it´s a more complex particles system than the glass itself?If it´s actually the inertia, Burgess describes the phenomenon perfectly: the whisky tries to remain where it was or the way it was, we could also say

I took out this book from the library. It was at the middle of the novel that I realized that I was reading the second volume. I thought a novel starting about page four hundred was a excentric and modern thing that I tolerated