Inertia

People of all walks of life, but mostly scientists, love to discuss inertia. Okay, probably no one actually loves to discuss it, but I imagine it comes up from time to time. It usually comes up in the context of a moving object, as it is the tendency of that object to resist any change to its motion.

Think of a bullet; as it's careening through atmosphere and ozone, it doesn't really want to slow down and most of nature is obliged to comply.¹ You are inclined to kindly step out of the path of the bullet and the bullet is inclined to tip its hat at you as it screams by faster than the speed of sound. The sound of the bullet, meanwhile, is struggling to catch up, trillions upon billions of bumbling air molecules bumping into each other as fast as they can. They give you a cursory glance as they stumble past and your ears pop.

Some people, like the moving bullet, might be said to have a high level of inertia. Figuratively. That is to say, they like to stay moving, and once they start, it's hard to stop them. These people seem to always be moving, doing, talking, walking, saying, playing, starting, finishing. They may tip their hats at you as they fly by faster than sound.

But the bullet wasn't just always tearing across the embankment or zipping down an alleyway. It was, at an earlier point, comfortably at rest inside the chamber of a gun. In fact, the bullet was so comfortable and so at rest there that, had it not been for an exorbitant explosion, it probably would be sitting there comfortably at rest forever. Rather than kindly stepping out of its path and rubbing your ears as the sound of it (trailing behind considerably) dawdles past, you would be sipping tea somewhere across town with no knowledge that there even is a bullet. This is another property of inertia, that of a stationary object that is inclined to remain stationary.

And just like moving persons, there are stationary persons. They are comfortably at rest inside their chambers. In fact, they are so comfortable there that, if not for an exciting explosion, they probably will be sitting comfortably at rest forever. You won't have to kindly step out of their paths, because they are on no path whatsoever.

Both types of bullets (the lethal, faster-than-sound kind and the harmless, comfortably-at-rest kind) are said to have inertia. Two contradictory states and one word to describe them both. It almost seems to invalidate use of the word entirely. What is the point in using a word to describe something if it can also be used to describe the very opposite?

And what about people? The always-moving-doing-talking-walking-saying-playing-starting-finishing person has inertia, just as the stationary, on-no-path-whatsoever person has inertia. You and I both have inertia. It all comes down to what that inertia means. It's the tendency of any object, moving or stationary, to resist any change to its motion or lack thereof. People waiting around comfortably for an extraordinary explosion to set them on their course may find themselves waiting an awfully long time.

¹ We're ignoring drag and friction.