Actually, every
action has an equal and opposite reaction.
If you sit on a sled on some ice and throw a brick, the action is the brick moving. The reaction is you moving. The only force involved is the one your muscles created. That force is directed from your hand towards the brick. It is not directed from the brick towards your hand.
On anything that spins, the action is pulling inward to prevent outboard masses from flying off tangentially. The reaction is an equal and opposite pull on the hub. This is balanced on spinning things whenever possible. The force is the mechanical force the hub exerts (tension) on the masses.
Compare these two definitions from Encarta:
Encarta's Definition of Centripetal Force
Encarta's Definition of Centrifugal Force
Check out Encarta's Encyclopedic entry on centripetal force.
Encarta Encyclopedia: Centripetal Force
Here's one I don't fully agree with because it confuses a few terms, but it still supports what I'm saying.
Encyclopedia.com: Centripetal Force
You may not trust those sources, but surely you'll trust PBS.
PBS.org: Centripetal Force
There are many more reliable sources, if this isn't enough. I haven't yet found a reliable source that contradicts.
Matthew.
[ 29 November 2001: Message edited by: heedm ]