Why does the rainwater sheet together where my windshield wipers have recently passed, but bead together where they haven’t?

Question

[Kind of crappy visual aid](https://i.imgur.com/zrzlYkW.jpeg)

I’m sitting in my car, procrastinating going inside because of the rain, and I noticed that the rainwater is behaving differently depending on the area where the windshield wipers passed and where they haven’t.

Why is that?

In: 91

Answer 1

Because the glass that doesn’t get wiped with the rubber blade is more perfectly smooth, & doesn’t break the surface tension of the droplets. The wiped area has been scratched by the blades & the droplets “wet” onto the surface more easily.