Fortunately, there are several easy ways to visualize this interplay. These demonstrations are fun to do and fascinating to watch, and they help you understand convection currents.
First, fun times with convection currents in water!
You get yourself two bottles with narrow openings (these are vintage whiskey bottles from the old dump in the back of our woods, because I'm just that hipster and also that's what I had on hand, but plastic soda bottles would work just as well). In the bottom of each bottle, you put some liquid watercolor or food coloring. Choose colors that will blend well.
Start your kettle and make up a separate bowl of ice water.
When the water in the kettle is hot and the water in the bowl is cold, pour hot water in one bottle and cold in the other, filling both up right to the brim:
If possible, do this outside because you're going to spill.
Use a sheet of plastic or a playing card to cover the top of the cold water bottle, then upend it and carefully balance it upside-down on top of the hot water bottle. Slide away the playing card, and watch the magic happen!
The cold water really wants to sink, and the hot water really wants to rise. Making them both do it through that one narrow opening gives you a chance to see it well:
We tried our best to leave the bottles like this for an hour or so, and over that time, as both temperatures of water even out, so will the color:
The next demonstration is hot water on top and cold water on the bottom:
There's nothing between them in that above photo--they just don't want to mix!
Give them some time, though. Look carefully in the below photo, and you'll see that the cold liquid is beginning to rise up, as the hot water cools down:
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| The level of water keeps dropping because the kids keep bumping the table and knocking the top bottle off... |
Oops! The kids had the idea that maybe we could open the freezer drawer, put the light above that, and perhaps get enough of a heat difference that way, but that, too, was a bust. Fortunately, I also baked some muffins that day, and when I opened the oven door I had a revelation, called for both kids, and we dangled the spiral over the open oven door. There was so much wind that we could feel it on our faces, as well as see it in the mad spinning of the spiral. Success!
The convection currents that we made in a fish tank, though, were by far the best, and this demonstration has turned into something that is living on our kitchen counter for a while, because it's so fun to play with and experiment with and explore.
All you need are a fish tank or clear plastic bin with any amount of room temperature water inside, ice cubes made from colored water, and a different color of food coloring or liquid watercolor.
On one side of tank, drop just a few drops of liquid color. On the other side of the tank, gently place a few of the dyed ice cubes:
Observe:
You will see the cold, colored water sink and drift below the room temperature colored water:
You can experiment further by adding more ice cubes in different locations, gently pouring in dyed very hot water, and any number of other interesting possibilities, each time spending some time observing carefully to see what happens to the currents:
In the below photo, Syd had poured in a bunch of clear ice cubes, and Will had poured in a couple of cups of nearly boiling water, dyed black. And look--they made a thunderstorm!
The kids did all the other demonstrations with me happily enough, but they LOVED this last one. LOVED it. Will is applying for a Space Camp scholarship again this year, and she's already thinking about how she can transform this concept into an original experiment. The kids have more colored water in the freezer, and they're planning some more exploration later tonight.
It's the best kind of homeschool project: hands-on, sensory, cross-curricular, open-ended. It's fun enough that the kids might even forgive me for the book reports that I'm also making them write!
P.S. Want to know more about wind currents? Here's where we played with Bernoulli's Principle and built giant geometric shapes!
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