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

Wipers clear sediment left on your windscreen that water can attach to, essentially, the bits that aren’t wiped have a thin layer of sticky sediment