Why does driving a screw in spurts work better? When you drive screws into wood with a driver or drill, it is often the case that mid-way through the process the screw will suddenly bind and eject your bit (assuming it's not a Robertson or Torx).
My father-in-law showed me that if you simply drive in little spurts, it will go all the way in without binding.
Now generally, the CoF is higher for static than dynamic, so it would seem this is not simply frictional.
Anyone know for SURE why that is? I can make any number of speculations (heat related almost certainly) but I'd like more than a guess.
 A: The wood you are driving the screw into has a relaxation time of order ~ 1 second during which the cellulose fibers and the lignin resin deform slightly to relieve the pent-up stresses they experience when the screw is initially being driven in. This slightly relieves the clamping force that the wood exerts on the screw, and it becomes slightly easier to drive further- until the screw gets clamped again.
I have found that dense and stiff wood (oak is the perfect example) doesn't relax like this, and the instant the screw driver tip jumps out of the screw you have to back the screw all the way out and either rub a bit of bar soap on the threads and drive it in again or drill out the pilot hole one step bigger.
A: I partly disagree with Niels' answer because the phenomenon you describe can occur in materials with widely ranging relaxation times.
I think, as the comments suggest, that an equally important phenomenon is the ability of the user to react to changes in the resisting force. Your screwdriver will "jump" if there's a sudden change in the resistance (or if you drift off-vertical...) .  By applying very short bursts, you avoid having to react to such changes in "real time."
A: When the screw is moving the friction force is smaller than when it is at rest. This answers the question in the title.
When the screw is driven in, it and the wood around it heat up, which increases the friction. The pressure on the screw also increases. The three effects results in the screw suddenly blocking. After a second the heat dissipates, the wood may relax a little, as argued elsewhere, and can be driven in further with increased force. Predrilling will mitigate this.
