Physics: What is density anyway?

This week we explored what density is. We started with a comparison of STUFF vs SPACE (i.e. mass vs. volume). Then we measured the mass and volume of 6 different objects. Measuring the mass was pretty straightforward...we used a scale. Measuring volume was a different story. To measure the blocks we used a ruler to measure each dimension and then multiplied them together, and for the irregular-shaped objects, we dropped them in a graduated cylinder filled with water and recorded the subsequent change in volume. Now for the HARD part! To get an idea of just how much STUFF is in a given amount of SPACE, we calculated the density by dividing the mass by the volume. Finally we put each object in water and noted whether it was a sinker or a floater. The coolest part was noticing that the density of all the floaters was less than 1 g/ml and the sinkers were all greater than 1 g/ml, and from this we inferred the density of water - 1 g/ml.
Not an easy lesson, but hopefully it will eventually SINK in!