Xandra was finding that Science was not so hard after all. She already understood MASS and GRAVITY. Xandra thinks she might like to become a cosmologist as well as being a vet and having her own pet shop. Her adventures with SpaceBoy make her an ideal candidate for this career. A cosmologist is a person who studies the Universe, and may also be a scientist or a mathematician or an astronomer or just someone who has deep thoughts about all of this. Just like Xandra.
VOLUME is how much space a thing takes up. Dad has a lot more volume than Mum, and Mum has a lot more volume than Xandra.
"You measure volume by how much you displace."
Xandra loves displacing water. In the pool she displaces it all over the place!
When Xandra practices her "star float" in the pool If she takes a big breathe she floats just under the surface. That is because she is slightly less dense than water. Water is denser than she is. If she was more dense she would sink.