第一件事就是要求出面积元。

OK, so the first thing to do is find the area element.

youdao

一个平面物体的密度是每单位面积元的质量。

The density for a flat object would be the mass per unit area.

youdao

即考虑曲面的面积元δ

S Namely, you would consider a small element of a surface delta S.

youdao

我们计算的是，整个区域的面积微元dA的总和。

Really, what we are doing is summing dA over the entire region.

youdao

我们计算的是，整个区域的面积微元dA的总和。

Really, what we are doing is summing dA over the entire region.

youdao