Using syringes, students determined if both air and water are compressible. Being word "smithers," students discovered that compressible means being able to push together. Therefore, something that is compressible can be squeezed or pushed into a smaller volume.
Students are also working on the practice of modeling to explain how one type of matter IS compressible and the other is not! We're looking not just at the visible level, but at the particle level, too!