Sorry about the absence. Between moving, a PhyzVan failure, a workshop, moving, a wedding, and moving, the blog had to simmer.
When teaching the concepts and subtleties of inertia and Newton's first law, I like to include some information on the understanding of the first law before the time of Newton. So I include a few relevant historical references.
1. "The cessation of motion is due to the opposing force…. If there is no opposing force…the motion will never stop."
2. "It is impossible to say why a body that has been set in motion in a vacuum should ever come to rest; why, indeed, should it come to rest at one place rather than at another. As a consequence, it will either necessarily stay at rest or, if in motion, will move indefinitely unless some obstacle comes into collision with it."
Both references precede Newton's Principia by about 2000 years.
Reference 1 comes from the Mo Ching, published in China approximately 2400 years ago. The source of reference 2 is a little more shocking.
When posed to groups of physics education professionals, I've never had anyone correctly identify the source. Some guess Newton, others guess Galileo. And these are smart people--many of them much, much smarter than I'll ever be. I'm pretty sure many of them don't believe me when I tell them the source.
The point of the lesson is a fundamental truth stated eloquently by Alfred North Whitehead: "Everything of importance has been said before by someone who did not discover it."