關於「密度」Densities

「密度」Densities是甚麼來的？
Denisty, defined mathematically as the ratio of mass to volume, measures how compact a substance is.

為甚麼密度高就沈，低就浮?
This is a result of Archimedeus Principle. A low density material object immersed in a high density liquid displaces a volume of liquid that weights more than the object itself. That is, the upthrust acting on the low density object is larger than its weight. The object thus floats.
[you could refer to any physics textbook for the mathematical derivation of this result],

油的密度不是很高的嗎?為甚麼水的密度比它還要高?
As said above, density measures the compactness of a substance. The compactness is, in fact, depends on how close the molecules in the substance are from each other (i.e. intermolecular separation), and the mass of each molecules. Water molecules are more closely packed, thus having a higher density.

oil has higher viscosity, not density

密度是形容該物質粒子排列的情況

公式：密度=質量/體積

油的密度是比水低的，所以油才會浮在水上。

密度白話說法：

一間教室擠滿100人跟10人，

100人那間密度是大於10人那間，

當體積一定時，

密度大者，

重量愈重，

故比密度小（重量輕）者重，

就會比他沉...


油密度比水小，

故油浮於水上...