These videos are pretty short, yet provide a wonderful, concise summary of how simple Newtonian mechanics alone can refute creationist claims that the earth / universe / whatever else they can think of is all 6,000 years old:
First we start with a brief description of rotational mechanics:
… how it applies to asteroids, and what it means for the age of the solar system:
And Rich, I’m sure you’ll correct me if I’m wrong on anything … )
The short short version is this: there are approximately 25 million asteroids orbiting the solar system that we know of, and we’re able to track the larger ones’ orbital paths and even their rotational frequency. Some, which rotate about their principal axis (the axis with the highest moment of inertia), do so with a regular, predictable frequency. Others, which don’t rotate about the principal axis, are in a “tumble” and thus have a very irregular rotational frequency. Either way, we can tell how they rotate by the amount of light reflected by its constantly varying reflective area.
So what? Well, if an asteroid rotates about its principal axis, the force on each element of mass due to spin is in equilibrium with the forces of gravity holding it together. If it’s tumbling, the magnitude and direction of the spin vector changes those forces, resulting in energy dissipation because of internal friction, inertia, etc.
In other words, a tumbling object will eventually dissipate enough energy to rotate about its principal axis, because that’s the lowest possible energy state. How long it takes depends on the average diameter of the object and its rotational period. The author gives four examples:
Earth: 17 yrs.
433 Eros: 100,000 yrs.
25143 Itokawa: 929 million yrs.
4179 Toutatis: 60 billion yrs.
Guess which one is still tumbling? That’s not the only one. To date, over 1,000 asteroids with rotational damping times many orders of magnitude longer than 6,000 years have been measured, and they’re all rotating about their principal axes. In fact, you can come up with a pretty reasonable upper and lower bound for the age of the solar system using this approach.
So, just another interesting bit of science to throw at you. The fact that it’s being used as yet another way to refute some of the ridiculous claims of creationism is just gravy. Thanks again to Ozmoroid for making these videos. Check out his entire playlist … he has a lot of good, solid educational material that doesn’t take a long time to go through. He reminds me exactly how much I’ve forgotten since I graduated from college …