Recently I was plotting bitmaps in 3D space, trying out various kinds of motion: linear, curved, inertial…and it got me thinking about how motion was integrated into interfaces.

Take the simplest, most common example: the sliding-out motion of a drop-down or fly-out menu…

Even though I now turn this effect off when I can (it's too slooooow), I was captivated the first time I saw it. Why?

Basically, motion implies weight, and weight implies thingness…and the sliding felt right because the menu is a thing I'm handling. So the motion functions like a kind of drop shadow for user interaction.

Inertial motion–easing in, a Flash staple–feels especially right in this context, because objects with inertial motion are more natural–on earth at least, things with weight come to a stop. It also nicely combines an intitial burst of speed with an ultimate delicate accuracy (the easing in).

When I was working with 3D, I was surprised to find linear motion fetching too…even as an object recedes and its 2D speed slows, your mind knows its 3D speed is constant. It vibrates with sustainable energy, like Stereo Lab, or Bach, or whatever your working music is.

Linear motion is great in 2001, but it clearly wouldn't work in an interface. An object in constant motion isn't an object you handle…and if it stops, where does that energy go? Our minds would add a clank and a shake if a menu slid out in linear fashion and just stopped.

Motion is a powerful tool to orient users…and disorient them, of course. Does motion makes "things" on the screen separate, self-propelled things, or things we can handle, tools?

Obviously, both…the trick is to separate or mix them for the particular experience you are trying to create, right?

If you work at a company with an intranet, I'll bet you remember the first time you called the IT guy for help and he (smirking?) started using remote desktop and wagging the cursor around on the screen and telling you how to fix the problem. It's a creepy moment, and a feeling of disembodiment, when your motion, your cursor and your power, is transferred abruptly to him.

Flash makes me feel that way, a lot.

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