Here's why:
* Density is defined as mass per unit volume. This means it tells you how much mass is packed into a specific amount of space.
* The composition of a substance determines its density. For example, water is always made up of two hydrogen atoms and one oxygen atom. This fixed composition means the mass of a certain volume of water will always be the same, regardless of how much water you have.
* Changing the amount of a substance doesn't change its composition. If you have a small amount of gold or a large amount of gold, it's still made of gold atoms, and the density will be the same.
Think of it like this: Imagine you have a box full of marbles. Each marble has a certain weight and size. If you add more marbles, you'll have more weight and more space taken up, but the weight per marble (density) will stay the same.
Exceptions:
* Temperature can affect density. When you heat a substance, its molecules move faster and spread out, increasing the volume. This means the same mass now occupies a larger space, resulting in a lower density.
* Pressure can affect density. When you compress a substance, you force its molecules closer together, decreasing the volume. This means the same mass now occupies a smaller space, resulting in a higher density.
In summary: Density is a fundamental property of a substance that depends on its composition and is not influenced by the amount of the substance. However, factors like temperature and pressure can affect density.
