I was driving home today in my car, which had been parked in an exposed spot with a cold wind on it. It was very cold when I got in. I turned the heater (water valve control) on full but only had the fan on '1'. After a couple of miles, the engine thermostat cut in and the water temperature blipped up to 60 or 70 C but I was not getting any obvious heat into the cab. I went fast round a roundabout (traffic circle) and suddenly a load of warm air engulfed my head. The warm air from the heater must have found itself up near the middle of the roof above my head and was suddenly displaced by the cooler air lower in the cab due to the centripetal acceleration of the car. As I turned sharply, the force was clearly enough to 'slosh' the air about inside. I managed to repeat the affect a few times but the air all warmed up eventually and it stopped. The effect was the same that you can easily get with a Helium balloon (which leans into the curve) but was 'invisible', in this case. This is a really cool effect and I have never experienced it before, in years and years of winter driving. I shall try to repeat the trick again. I think it would not work well with the fan turned on high because that will just stir up the warm and cold air layers too much. Has anyone else noticed this? It's an uncanny experience and worth trying for. The faster you turn, the better - so be careful of icy surfaces.