The answer is in the water

Its been a busy old day.
We went to a science centre in Sheffield, housed in a former steelworks. They have kept the steel works in its original industrial condition but superimposed four pavillions inside - water, air, earth and fire.

This exhibit was in water. The little boy weed in one of two buckets to show "true" or "false"

Hollie was quite disgusted by his "thingy"