Great lab that ask the question: Which is better for measuring the amount of matter? Mass or Volume? Students fill water balloons (with a different mass sinkers) in each balloon. They put a set volume of water and mass the balloon before and after you freeze the balloon. Obviously, they have to wait for the next day to have a frozen balloon. They each group plots change in mass and volume on a class histogram. Great lead up to density because it shows water changing volume and you can relate this later on with density.