We also are digging deeper into understanding the difference between weight and volume. We compared two materials in our lakes (water and sand) and discovered that even though we measured the same weight of the materials, they took up quite a different amount of space, indicating that they had different volumes for the same mass. This is introducing the concept of density as "heavy for size." Sand is heavy for size since it occupies less space for the same mass. Therefore, sand is more dense than water, and therefore, it sinks!