Wheels and Soap
My bike wheel is out of round. It's not that bad (I've ridden on worse), but it's bad enough that I'm actually excited about getting it fixed this weekend. (I don't know how to true a wheel.) It's fine left-right, so the breaks work, but there's one spot that's flat instead of round, so there's a functionally a big dip every revolution.
The way that this manifests while riding is basically the same as going over a bump in the road. When I am going over bumps in the road I can't tell them apart from the bump in the wheel. But what's interesting is how much more annoying the bump in the wheel is than going over a bumpy road. If my entire ride were on a bumpy road it wouldn't bother me at all, but when I have the cyclical "thud-thud-thud" from the bad wheel it's incredibly distracting.
I've been wondering why this is. Perhaps it's similar to the difference between white noise and periodic mechanical noise. Our bodies are used to chaotic and random inputs but when inputs become regular the brain assumes something's wrong. I'm not really sure, but I thought it was an interesting observation.
I sometimes wash my hands with soap, but mostly don't bother. I've noticed that how many paper towels it takes to dry them varies, and the most important factor is whether or not I've used soap. I hadn't ever given this much thought, but today decided to. It seems pretty obvious that the reason is that soap removes the oil from skin, and oil is hydrophobic and repels water. So removing the oil makes water stick to skin better, hence needing more paper towels to dry my hands.
As I said, this is obvious, I just hadn't really thought about it before.