why does ice cubes flip over when placed in water?

Answer 1

When ice freezes it absorbs gas from the air (the solubility of gas in water increases as the temperature drops). Because of this there is more dissolved gas at the top of the ice cube than at the bottom. If placed in a drink with the gas-filled top of the cube facing down, it will flip over since the part of the cube with more dissolved gas is lighter.

Answer 2

If you are talking about when first dropped in, it is finding the most stable way to float which is a bit tricky for a rectangular solid.
If you are talking about later, ice is less dense than water, which is why it floats with 9/10 of the cube under water and 1/10th out. But when sitting on the surface, cold air chilled by the cube hugs the surface while cold melting water falls away from the cube underneath, so the bottom melts much faster, making the bottom smaller. With less ice, it sinks somewhat, but eventually the cube gets top heavy and flips over.

Answer 3

it doesn't necessarily melt uniformly. the smaller it gets , the more and more unstable it gets. it's just trying to find equilibrium/most stable way to float.