We took three glasses with water (three quarters more or less) and we decided to change them according to density levels. How did we do it? First of all, we kept the first glass only with water (now salt in it). Afterwards, we poured a little bit of salt in the second glass. Finally, we poured a lot of salt in the third glass. In the second step we added three drops of food colouring to each glass.
What happened? The food colouring sank in the first glass (it had more density than water). The food colouring was kept in the middle in the second glass (water and food colouring had a similar density). The food colouring floated (was kept at the top) in the third glass (water had more density than food colouring).
DON'T WORRY, THE EXPERIMENT IS EASIER THAN IT LOOKS!