Change in state(from liquid to solid) and change in colour I believe.
Objects are known to go down because of a unbalanced force
The ice cubes were floating in water because they are less dense than liquid water. When water is frozen, a structure that is crystalline is formed that is held by hydrogen bonding. Due to the orientation of these bonds, the moleules would push far away from each other causing it to have a bigger volume and a lower density.
