why is that even if it’s Super hot and sunny outside, The air will feel cool if you stick your arm out of the window while driving?

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Answer 1

The moving air evaporates moisture on your skin. The evaporation process actually takes some heat from your body with it. As long as the air is not significantly warmer than your body temperature, this evaporative cooling effect will be stronger than the convective hearing from the moving air.

However, I can tell you from experience that if you roll down the window in 130 degree weather and stick your arm outside while moving, it still feels hot. It has enough thermal energy that it far exceeds the evaporative cooling that is taking place and simply feels like a blast furnace.