Answer the following questions related to the idea of density and floating:
(a) Define density and state its SI unit.
(b) A piece of candle wax and an iron nail have the same size and shape. Both are dropped gently into a bucket of water. Which one will float and which one will sink? Give a reason based on the concept of density.
(c) Sea water is denser than river water. A wooden raft floats in a river such that 20% of its total volume is above the water surface. Predict whether the fraction of the raft that remains above the surface will increase, decrease or remain the same when the raft drifts into the sea. Explain your answer with reference to density.