Swimming in the Dead Sea

There are many empty spaces between the peas in which the sugar can sprinkle. If you do not take too much sugar and shake the glass gently, the sugar will totally disappear in the gaps between the peas. Thus the glass will not (or hardly) be fuller.
In fact the glass has not become fuller (the volume of the content has not increased), but the mass of its content has clearly increased.
If substances equal in volume but differ in mass, we say they are differently "dense". The substance having the greater mass is "denser" than the substance having the smaller mass.

The density of the mixture of peas and sugar is greater than the density of the peas alone.