I went for a bike ride this morning, the first real bike ride of the year (I’ve biked to and from work a couple of times, but this was the first real ride just for the sake of riding). There was some pissy drizzle at the start, but by the time I got on the bike path headed for Lock 8, the sun came out, and it was a cool, pleasant, calm spring morning.
As I was tooling down the path, I realized that I had the bike one gear higher than I usually do on that stretch of path, but I didn’t feel like I was working any harder than normal. “Gee, I guess I’m in better shape than I thought…” I said to myself.
Then I reached Lock 8, and turned around.
It turns out, I’m in just about exactly the shape I thought I was. What I was wrong about was the “calm” part of the weather description. There was actually a very steady wind blowing, that had been at my back the whole time (blowing from east to west, which is a little unusual, and why it hadn’t occurred to me as an explanation). When I turned around, I spent most of the ride back one gear lower than usual for that stretch of path.
So there’s today’s lesson on Experimental Physics for Morons: Wind resistance is a significant problem. Particularly if you’re 6’6″, 250 lbs– I’m around half a meter across at the shoulders, and nearly two-thirds of a meter from waist to shoulder, meaning that on a mountain bike, I’m like a giant goddamn sail.
Or, to be quantitative, the drag force on me is:
Fdrag = -0.5 ρ D(0.3m2)v2 = One bike gear