I found that if you drag a wooden block across a piece of 150 grit sandpaper, there is more friction than if you do the same with a piece of 50 grit sandpaper. Why is this? I tried to find an answer on the Internet, but they were not specific enough.
2 Answers
Short answer: finer grade sandpaper has more points of physical contact than rougher grade sandpaper, and each point of contact is a source of friction.
https://www.scientificamerican.com/article/how-do-flies-and-other-in/
Extrapolate from there and see how it would apply to 150 grit sandpaper compared with 50 grit.