热空气比冷空气密度小，因此热空气总在冷空气上方。
Warm air is less dense than cooler air so it ends up layered on top of the downward moving cooler air.
引擎将高超音速飞机带向空气密度、阻力比较稀少的高度。
That engine would carry the hypersonic craft to an altitude where air density and resistance are less.
大气压力随高度增加而降低，大气密度也随着高度增加而降低。
Atmospheric pressure decreases with increase in altitude and so does the density of the atmosphere.
应用推荐