Fill a plastic container (such as a water bottle) about one-third full of water. Add one-third oil (so the bottle is now two-thirds full) and cap the bottle. Shake it up and see if you can get the two to mix. (If you add blue dye to the water beforehand, it makes this experiment easier to view.) Which is on top, the water or the oil? Stick the bottle in the freezer overnight (stand it upright and remove the cap first). Now which is floating on top?  What else can you test out?