An example of rain clouds

Another super fun experiment of how density works in the water cycle. This one is so easy the boys have done it many, many times.

Fill a cup a little more then half way through with water.  Add oil until you have about a 1/3 of an inch sitting on top of the oil. Add one drop of food coloring.  It will fall through the oil sitting between the oil and water.

Add a pinch of salt and watch the food coloring fall to the bottom of the cup.  the very first time through it fell in a straight line exploding on the bottom...The salt making the food coloring the heaviest causing it to fall through the water instead of simply mixing into the water. But when you dump a spoonful of salt onto that drop of food coloring it takes not only the food coloring, but forces the oil down as well. 

And then we get to watch the oil float back to the top, kind of like evaporation. The boys loved it.