The car-bug connection

Dear Matthew Alice:

Say I trap a fly in my car when I go down the highway going 70 miles an hour. Why doesn't the fly get smashed against the back window, assuming flies can't fly at 70 miles per hour?

-- F.W., San Diego

M:

So I'm driving down the freeway, windows open, singing to the radio. Why isn't my car full of bugs when I get where I’m going? I don't even remember getting bugs in my teeth riding in a convertible.

-- The Roadmaster, San Diego

That slapping sound you hear is every high school physics teacher in the county whapping palm to forehead. When they taught you this stuff in school, nobody cared. Now that you've graduated, it's a burning mystery. Youth and education, wasted on the young.

So, F., as you zip down the street, the F.W.mobile transports you, that litter of sun-warped tapes, burger wrappers, and loser lottery tickets, as well as many cubic feet of air and your friend the fly. You're all in a capsule of air inside the car moving down the road more or less as a stationary unit, particularly if all the windows are closed. If the air itself (inside the car) was moving at 70 mph, among other things, your dog wouldn't have to stick its head out the window to reach that mysterious state of canine bliss a dog achieves when bugs blow up his nose.

But when the time comes that you want the fly gone, then I suggest you open all the windows. Roadmaster's fast-moving car driving through a swarm of mosquitoes will push the bugs out of the way like a boat pushing through the water. One thing the moving air does is create its own low-pressure zone around the car. As a rule, air moves from higher-pressure areas (inside your car) to lower-pressure areas (outside your car). So if you can talk the fly into hanging out near the open window, he'll be sucked outside before he knows what hit him.