In October the Explorers discovered that sometimes an examination of a fundamental science concept can put the emphasis on the FUNdamentals, with an activity that had everyone feeling perfectly bubbly.
Back in ancient times when Mr. Ramsey was a wee little lad, there was a period of time where contraptions called “Lava Lamps” were all the rage. People would stare transfixed at these glass tubes where glowing lava (well, wax) would float up and down in eerie-looking blobs. It looked like magic, but in reality a lava lamp was a simple application of the concept of density.
Density is simply a matter of how tightly packed together the stuff in an object is. Consider a bowling ball and a balloon blown up to the same size. The molecules in the bowling ball are packed much more tightly than the air molecules in the balloon, which is why the bowling ball weighs so much more. We say that something with tightly-packed molecules has a higher density, while in things with lower density the molecules are more spread out.
The trick to a traditional lava lamp is two-fold. First, things with lower densities tend to float atop things with higher densities (so a low-density piece of cork floats on top of water, but a marble with density higher than water sinks to the bottom). Second, most materials expand (get larger) a bit when they are heated—this expansion causes their density to decrease as their molecules spread out a little, but if they then contract (get smaller) back to their original size the density goes back to where it started.
In a lava lamp, you have colored wax sitting at the bottom that is slightly more dense than the liquid (usually some type of oil) filling the container. When the lava lamp is turned on, a light at the bottom starts heating up the wax. When the wax expands a little and its density drops to just below that of the oil, the wax rises to the top. Here, away from the heat of the light, the wax cools back down, contracts, and again becomes more dense than the oil—so it sinks back to the bottom. Then the wax heats back up and the cycle starts all over again, at least until you turn the lava lamp off and everything cools down.
The Explorers started their activity by testing out this concept of density. We poured some cooking oil and some water into cups, and observed how we could tell by the way they separated themselves (oil at the top, water at the bottom) that the oil was less dense than the water and therefore floated atop the water. Next we added a few drops of food coloring. The food coloring formed little blobs that sank through the oil (so food coloring is more dense than oil), but when the blobs touched the water at the bottom they broke apart and mixed throughout the water (proving that food coloring and water have the same density).
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Now it was time to turn all of this into our version of a lava lamp. We filled drinking water bottles with the same mix of water, oil, and food coloring, so that we ended up with colored water with a layer of oil above it in each bottle. Now we needed a way to get the colored water to rise and fall through the oil to mimic the wax in a traditional lava lamp. Our solution was to use bubbles instead of heat.
The bubbles came from the antacid medicine known as alka seltzer. When a bit of one of these tablets is dropped into water, it dissolves and forms lots of carbon dioxide bubbles. As these bubbles (which are less dense than both the water and the oil in our bottles) rose up through the oil to the top, the clear bubbles dragged a bit of colored water along for the ride. Once the bubbles reached the top of the oil and popped, the colored water sank back down through the oil. The whole process would continue for a minute or so until the tablet was completely dissolved, at which point we could start it all over again just by dropping in another tablet.
Once everyone had demonstrated their lava lamps, we turned the classroom lights off and illuminated the bottles from below or from the side with a flashlight as the bubbles rose and fell. Very, very cool.
At the end of the meeting everyone went home with their own lava lamp bottle and a couple of spare alka seltzer tablets, along with one word of warning from Mr. Ramsey: oil makes a nasty mess when spilled on carpets, couches, or pets, so be careful!
Check out the photo gallery for some pictures of our lava lamp activity, and click on the link below for information from previous year’s experiments with this.