This is an easy, quick results experiment that shows movement of water of different temperatures (convection). The warm water is less dense(lighter) than the cold water, so the warm water rises to the surface and the cold water sinks to the bottom. This is called a convection current.
We actually did this experiment twice with the same results, everyone wanted a turn and it was really easy to do again.
Large clear glass jar - we waited until we ran out of pickles :),
small jar - ours was plastic, the small neck is good to watch the water rise out.
Fill the large jar with cold water so the water will be above the height of the small jar (we added some ice for a few minutes to get it extra cold)
Fill the top jar to the top with hot water (we just used hot tap water, ours gets steamy and I didn't want burns) + add food colouring so you can see the different water temperatures - the more vibrant the food colouring the easier to see the convection.
Now you are ready. You could either attach a string to the top of your small jar to lower it into the cold water, or what we did it use regular kitchen tongs to lower it down and set it on the bottom.
Get right at eye level with the mouth of the small jar for the best viewing.
The explanation: When you heat up water, the water molecules start moving around faster and faster. They bounce off each other and move farther apart. Because there's more space between the molecules, a volume of hot water has fewer molecules in it and weighs a little bit less than the same volume of cold water. So hot water is less dense than cold water.
Very fun, but how does this relate to underwater smokers? Scientists have found really interesting vents in the ocean called Black Smokers. Go to NOAA's website to find out more and watch these cool videos. Also see the documentary on PBS.