Bike -> Drums

When you learn to ride a bike, adults tell you it’s easier to stay upright the faster you’re moving. I suppose some kids take this as license to rocket downhill, but I was never one of those kids. I always heard it as one of those lies adults tell you. I’ve never liked going particularly fast, and I always balanced just fine.

What I didn’t know at the time is that bicycles can balance even without a rider—and generally the faster they go, the better they balance. Now, there are arguments about exactly why bikes balance, with factors including the conservation of angular momentum, which makes it hard to twist a rotating object (like the wheels); a sort of drag on the front wheel that turns it in the direction the bike tilts, keeping it under the frame; and the distribution of mass in the frame, which forces it to fall toward the front wheel rather than sideways, even when the frame tilts. As interesting as that argument is, it won’t get us to drums. For that, we need the bike to fall.

You realize how heavy bikes are when one falls on your leg, but you also realize how loud they can be. They sure can clang, especially if they land on pavement. That clang comes from vibrations in the metal frame that start as soon as they’re hit by something hard like a rock. The more rapidly the metal vibrates, the higher-pitch the resulting sound. But you can’t easily change how quickly something vibrates by hitting it a little differently, at least not if you abstract away from the real world (as physicists are wont to do). Everything around us has its own resonance frequency—its own natural rate of vibration where it’s easiest for the atoms and molecules in the structure to exchange energy back and forth. Something’s resonance frequency depends on a bunch of stuff, and the actual sound you hear when something’s hit depends on even more stuff. But let’s keep abstracting away from that mess to find a good rule of thumb: If you have a bunch of tubes of the same kind of metal, longer tubes will make lower pitches when struck. The bulk of the frame will have a lower-pitch clang than the adjustable tube that the seat sits atop.

This is also true for the air inside the tube. If you blow over the top of a tube, longer ones will make lower notes than shorter ones. Pipe organs make music this way, as do flame-fueled Rijke tubes.

The source of all these sounds is microscopic vibrations, whether in the air inside the tube or the tube itself. All sounds are produced this way, even without a tube in sight. Sounds come from vibrations. And the rule of thumb holds true more widely, too: More material generally makes lower pitches because it’s hard to get a lot of stuff moving (as long as you keep everything else the same). The less energy it takes to get something moving in the first place, the more of that energy can go into vibrations.

This is why we can hear the difference between kinds of drums—say, between snare and bass. The snare drum is tiny and makes a high-pitched sound; the bass drum is much larger and makes a correspondingly lower-pitch sound. Admittedly, the drum heads might sometimes be made of different material, and also a snare often has stuff at the bottom to shake the sound up a bit, but that’s really neither here nor there.

And that’s the thread of continuity between bicycles and drums.

As a side note, I’m going to kick off this blog by doing one post a day for the first week, then I’ll settle down into the weekly schedule.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s