In the CUNY Matter & Energy curriculum, we weigh balloons with students. We do this by either balancing yard sticks on our fingers or placing balloons on a scale.
What is the definition of matter again? Something that has mass and takes up space. Is air matter? No… yes… I don’t know. Does it take up space? Yes, you can see it by filling a balloon? Does it have weight? I don’t think so… How could you prove that it does or doesn’t?
