為什么對(duì)著我們的手使勁吹氣能使它們變涼，而對(duì)著它們呼氣卻能使它們變暖呢?

為什么對(duì)著我們的手使勁吹氣能使它們變涼，而對(duì)著它們呼氣卻能使它們變暖呢?

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.

這主要是由于每種情況下的氣流速度不同造成的。當(dāng)我們用手慢慢地呼氣時(shí)，口腔中的熱量和水分有時(shí)間傳遞到我們的手上，使它們升溫。但是噘嘴吹氣會(huì)加速氣流，當(dāng)氣流經(jīng)過我們的手時(shí)，它會(huì)吹走任何與我們的手接觸而變暖的空氣，讓手變冷。此外，快速移動(dòng)的氣柱會(huì)吸入或“夾帶”周圍的空氣。這往往比我們呼吸的溫度低，所以它能增強(qiáng)降溫效果。