密度小的物质向上浮动并形成一层皮。

Less dense substances move upwards to form a crust.

《牛津词典》

施加给比自己密度小的物体的向上作用的力。

The upward force that a fluid exerts on an object less dense than itself.

youdao

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.

youdao

So again, this is an anti-bonding orbital, and what you see is that there is now less electron density between the two nuclei than there was when you had non-bonding.

同样的，这是反键轨道，你们看到当你有反键轨道的时候,两个原子核中间的电子密度更小了。

麻省理工公开课 - 化学原理课程节选

Because we know as we go to infinity, even though the density gets smaller and smaller and smaller, we still have electron density very far away from the nucleus.

因为我们知道即使到了无穷远处，尽管电子密度会变得非常非常非常小，但我们仍然有一定的电子密度，无论离原子核多远。

麻省理工公开课 - 化学原理课程节选

What the Dutch did--the Netherlands is an extraordinarily small country, and it's the most populated country in Europe, then, per square kilometre, and is now--once.

那些荷兰人...荷兰是一个,非常非常小的国家,也是当时欧洲人口密度最高的国家,如果以每平方公里人口计算,现在也是

耶鲁公开课 - 欧洲文明课程节选