[alfalfasprout]

To add to the other answer, that friction (and the intertia of the balance wheel) is actually factored in when regulating the watch. The pallet fork gives the balance wheel a nudge on every "Tick" then the pallet fork stays stuck until the balance wheel swings around and back and jolts it in the other direction (the tock). Basically a little bit of energy is released from the mainspring via the escapement to the pallet fork to the balance wheel on each tick/tock.