RE: Physics Lessons on the Median Strip

You're quite right - and many people I've spoken with that have AWD vehicles concur that it handles better than their older 2WD cars. The secret, of course, is to maintain positive contact to something grippy for all wheels. So long as those tires have frictional contact of some sort, AWD will function as it should. But like you said, when it hits pure ice, there's no real difference between the tire being on ice or the tire being in the air in terms of resistance.

It sounds like your center differential employed some sort of viscous clutch. The principle being that so long as the rear drive is turning at the same rate as the front drive shaft (all wheels = approximately the same speed) then it will rotate freely. When the front drive shaft begins to turn quicker than the rear (due to slippage), the viscous fluid begins to bind which causes the rear drive shaft to turn faster to equalize - thus transferring power to the rear wheels. It's essentially the principle of a limited slip differential put into the transfer case instead of at the axles.

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