为什么对着我们的手使劲吹气能使它们变凉，而对着它们呼气却能使它们变暖呢?

This is essentially due to a difference in the speed of the airflow in each case. When we breathe out slowly on our hands, the warmth and moisture from our mouths has time to transfer to our hands, warming them up. But pursing our lips speeds up the airflow, and as this passes over our hands, it blasts away any air that’s been warmed by contact with our hands, cooling them. In addition, the fast-moving column of air draws in, or ‘entrains’, the air around it. This tends to be cooler than our breath, so it boosts the cooling effect.

这主要是由于每种情况下的气流速度不同造成的。当我们用手慢慢地呼气时，口腔中的热量和水分有时间传递到我们的手上，使它们升温。但是噘嘴吹气会加速气流，当气流经过我们的手时，它会吹走任何与我们的手接触而变暖的空气，让手变冷。此外，快速移动的气柱会吸入或“夹带”周围的空气。这往往比我们呼吸的温度低，所以它能增强降温效果。