This is not the smartest thing, I have to tell you -- racing a bike through dark streets on a rainy night, doing amateur physics in your head when you should be watching for pedestrians and potholes. Nevertheless, curiosity gets the better of me, and I spend the whole trip trying to understand why I'm seeing what I'm seeing: Water from the pavement clings to the tire and gets lifted along its back side, breaking free near the top and being flung upward and forward in a spray of drops; they lose momentum, stall, and fall back to the street. But the arcs I see -- or think I see -- are what compels me: Launched into the air ahead of the bike, a drop of water should rise and then, slowed by gravity, curve forward and down. If the bike is moving, though, it overtakes the drop as it slows ... so the drop's trajectory seems ... relative to the bike's motion ...
That's as far as I get, because I've never actually taken a physics course. Physics always sounded like it involved math -- lots of math -- and I've had an uneasy relationship with math ever since we hit the seven-times tables in Mrs. Forbush's fourth-grade class. A chart on the wall measured each student's progress through multiplication with a row of gold stars, and my row lagged badly. In high school I struggled to comprehend the abstract x's and y's of algebra, although geometry was easy -- it was so much more real. I finally gave up at the end of pre-calculus, which I never got the hang of at all. No one suggested that I go on to physics.
But now I'm left wondering about all kinds of phenomena and epiphenomena, from gravity and motion to bridge trusses to why a long crack has opened up in the dining-room wall. What I know about physics -- and here I'm including mechanics, hydraulics, acoustics, and much more -- is mostly what I've deduced myself, along with what I've read about in the Tuesday "Science Times" section and what I've picked up from books and even plays. If a serious question arises, I consult my trusty 1944 Encyclopaedia Britannica, but not even that explains differential equations in a way that makes any sense.
Still, physics has me hooked. One of my favorite bike rides takes me up a steep hill in Rock Creek Park here. The road climbs a long switchback that is hard work to go up and pure adrenaline-rush exhilaration to come back down: You descend as if flying through the trees, banking gracefully from curve to curve as your speed builds. By the time you reach the switchback itself, you're low over the handlebars, pedaling hard, leaning sharply to the left, and at the tightest point of the turn you feel a sudden lightness, as though you had outrun gravity.
The sensation is momentary, over almost as soon as it has begun. I can't explain it -- I can't even swear it's real. For all I know, it might be a product of the adrenaline rush. Or perhaps momentum's pull to the right in that turn is so strong that the familiar tug of gravity seems weak by comparison. In any event, the switchback helps me understand why the likes of Galileo and Newton had to invent physics: How could the curious not wonder what governed their own motion, or that of a bell rung by a boy in a church tower, or an apple tossed in the air, or the wind when snowflakes made its currents visible?
The sciences are encrusted now with journals and institutes and advisory committees and theories so arcane it takes teams of science writers to translate them for the masses, but I suppose they all began as common curiosity and close observation. The Babylonians had a rich tradition of astronomy thousands of years before the telescope existed; Aristotle observed and recorded the habits of fish and whales, among other creatures; Leonardo filled notebooks with drawings that show how water behaves under various circumstances, with theories about planetary motion thrown in for good measure. You can never spend too much time observing what is around you.
Lately I've been preoccupied with a kind of personal physics of deterioration and decay -- a science by which I would once and for all explain that crack in the dining-room wall, and holes in socks, and the short life spans of Walkman headphones, and temperamental behavior by certain computer applications during times of stress. Any material thing that is not alive -- that is not refreshing itself overnight, say, or being renewed every spring -- everything else seems to me to be deteriorating at some predictable rate. This, I think, is why potholes open up every winter on Columbia Road to reveal long-buried streetcar tracks, and why bike tires go flat for no apparent reason while you're out of town for a week. Relentless cycles of heat and dampness and motion take their toll on everything. But because they do so slowly, and because we live so much in the moment, we tend not to notice the deterioration until the headphones die or the heel shows through the sock.
It's important to me to understand this, because as I grow older I see that maintenance is among the most essential of human endeavors, even though it was never discussed in Mrs. Forbush's class, or Sunday school, or four years of a fine liberal-arts education. Now it sometimes feels as though I do nothing but worry about oil changes and slow drains, and I want to understand why. It's a lot easier to spend a weekend repainting trim if you can explain to yourself why it was peeling.
All of that is what I don't know about physics. The silver lining is what I've realized I do know -- or what my body knows for me, at least. On paper I labor over the most rudimentary equation, but on my bike I can calculate at a glance the speed of oncoming cars in Dupont Circle, and figure how fast I need to be going to merge into traffic or to bolt through it. On foot, I know without even thinking about it how much effort it will take to jump over a puddle by the curb or to take the first three stairs of a flight all at once. I couldn't begin to explain the math this involves, even though at some level I must actually be doing it -- be doing it every day, dozens of times, unconsciously and at the same time that I'm also humming Mozart and thinking about lunch.
Most of us don't think about physics much -- we have meetings to go to, so many meetings, and expense reports to fill out, and e-mail to answer, and at the end of the day who wants to curl up with a volume of Galileo or Newton or Einstein? Still, there are phenomena and epiphenomena to think of, and sprays of water to watch, and it never hurts to tease the brain into activity. I recommend a few lines of fluid mechanics, from Tom Stoppard's play Arcadia:
THOMASINA: When you stir your rice pudding, Septimus, the spoonful of jam spreads itself round making red trails like the picture of a meteor in my astronomical atlas. But if you stir backward, the jam will not come together again. Indeed, the pudding does not notice and continues to turn pink just as before. Do you think this is odd?
THOMASINA: Well, I do. You cannot stir things apart.