https://www.bbc.co.uk/bitesize/topics/zc89k7h/articles/zytqj6f
https://www.youtube.com/watch?v=X2qadk5mm0k
https://www.youtube.com/watch?v=4dx3l7vnskE
EXTRA - If you're interested in Archimedes' challenge & discovery, watch:
https://www.youtube.com/watch?v=0v86Yk14rf8
