My work generates a lot of what is nicely spoken of as "household hazardous waste." This includes empty paint cans, empty solvent bottles, and empty spray paint cans. It's not really too hazardous, but it's classified that way. I collect these in paper bags and save them for recycling, along with the many pounds of bulk mail, catalogs, and magazines that I receive every week. The papers can go to the local recycling center, but the paint and spray stuff must be taken to a special place where it can be handled and disposed of. So I wait till I have enough of it, and then make an expedition in miles of heavy traffic to do the job.

I made that expedition yesterday, and found to my dismay that the "household hazardous waste" recycling center had closed just a half hour before I arrived. So I had to leave with what I came with, including about a dozen empty spray paint cans, all in bags in the Narenji Orangecar's cargo bay. Now don't worry, they won't blow up, and they won't leak noxious vapors; the stuff is well sealed. But it is there, and it's taking up space.

Spray paint cans have a ball bearing or other metallic chunk in the canister, which agitates and mixes the paint when you shake the can. When the can is full, and you shake the can, you can hear the metal sphere clacking around in the paint, against the metal cylinder. Now imagine that the paint is gone and there's nothing left inside the cylinder except a bit of leftover paint, gas, and that metal ball. There's nothing to stop that thing from clanking around inside the canister and making a racket. And now, imagine twelve or more of these things all in my car, and all of them going at once. It's ambient noise for cheap! It's a gamelan of garbage! And it's in my cargo bay, until I can get back to the recycling center when it's open.

But why do these things make so much noise when I'm driving along with them? They don't make noise when they're sitting still. Nor do they make noise when I'm driving at a steady rate. That was the telltale factor. It's physics! I have not forgotten my first year physics. What I have in the back of my car is two bags of unofficial accelerometers.

The cans, stuck in the cargo bay, move as fast as my car. But the metal bearings inside the empty cans are free to move and have inertia of their own. So that when I accelerate, or change direction, in other words change vector, the metal ball will not move with my car but will tend to stay in its original course, and thus be knocked against the wall of the can, with a very audible "clink." This will happen whenever my vector changes, or whenever my acceleration changes. If I stop, the metal is going faster than my car and will hit one side. When I speed up, it will hit the opposite side. But if I maintain a steady speed, they settle down and make no noise, because things moving at a steady speed or constant vector are not changing motion and thus maintain stability in relation to each other.

But to make things more complicated, the cans are not stacked in even rows. They are stacked at many angles in the paper bags, because my packing is not neat. Thus each can that is not lined up in the same row will have its own vector to follow, and its ball will not hit the can at the same time as the other ones. If I had them all lined up in a row, they might clink in unison. But with the more random stacking, there is a rhythmic chorus of them every time I speed up, slow down, or turn. This can be entertaining on short drives. In a longer drive through the start-and-stop traffic of the city, it is less entertaining. The clamor will give me the force to vector my car back to the recycling center as soon as I can find the space-time to make the journey.

Posted at 3:45 am | link