Joe runs a popular blog with lots of neat stuff, but I have to pick a nit here. Well, honestly I think it’s more than a nit.
When something spins while being tethered in place by gravity, its mass wants to fly outward into a pizza-like shape, like frosting flying from errantly-aimed eggbeaters.
This is vague, at best, but at worst it reinforces a misconception about circular motion. If by “outward” you mean straight out, i.e. radially, then mass in circular motion does not want to fly outward. The only force on the mass is inward, which is gravity. If you “snipped the rope” or turned gravity off, the mass would want to go in a straight line, tangent to the circle it was traveling in. Now, that line increases in distance from the center, so in that sense the motion is outward, but I think the vagueness of such wording is counterproductive, because it can reinforce a misconception so easily.
You might ask, “What about the centrifugal force?” Well, that’s a fake force we put in place when we are in a rotating coordinate system, but want to pretend. We pretend that we can still apply Newton’s laws, and we pretend our motion is a straight line. As such, the net force has to be zero, so we pretend there’s a centrifugal force that balances gravity. But that force really isn’t there, as forces are defined. It’s an illusion of being used to inertial reference frames and trying to make sense of motion when suddenly you’re not in an inertial frame. (The Coriolis force explanation is similar to this, owing to the rotation of the earth)
And that batter flying off the egg beater? Take a look at the pattern it makes on the bowl. Is it perfectly round dots, which is what you’d expect from flying straight out, or is it somewhat elongated dots or streaks, from something moving in a tangential straight line, hitting a curved surface? (This week on CSI: Kitchen)
http://xkcd.com/123/
The centrifugal force isn’t imaginary, and in a rotating frame turning off the centripetal force does result in a radial outward acceleration. The Coriolis force kicks in, though, and bends the path in the rotating frame, though, making it match the result in the inertial frame.
Certrifugal or centripetal, it/they vanish the instant the test mass is no longer attached – then, Newton in free space. Transverse Doppler effect in an ultracentrifuge hub vs. rim is inert toward rate of time passage for an ascending photon,
Phys. Rev. 129(6) 2371 (1963)
The Beckman Coulter Optima MAX-XP ultracentrifuge delivers 1,019,000 gees on a desktop for 700 watts; in French, Italian, German, Spanish, Russian, Japanese, Portuguese, Chinese, and presumably English. Frame dragging, anybody?
@BlackGriffen
Sorry, but in the context of Newtonian physics, the centrifugal force is imaginary. To claim otherwise violates the first and third laws. You have curved motion with zero net force and there is no reaction force to pair with it.
I’ll go further and say that it’s plain wrong. The outward ‘centrifugal’ tendency doesn’t cause all orbiting bodies to favor a single plane of revolution. Even if every revolving body had a different inclination, the forces are in balance.
Only when you consider collisions and tidal interactions to things tend toward a common plane. Somebody else posted a much better description in the comments.