Does Water Fill a Cup

Is a cup full of water really full of water?
- Amanda (age 12)
Sir William Van Horne Elementary School, Vancouver, British

I guess what you’re asking about is whether there are spaces between the water molecules. The molecules don’t have sharp boundaries, since their electron clouds gradually tail off. That makes it a little arbitrary to say where the molecule stops, and whether any of the space is ’empty’. So it might be best to just use the words in the standard way, and say that a glass full of water is full of water.

Mike W.

(published on 10/22/2007)