Make Your Own "Lava Lite"
1. Pour about 3 inches of water into the jar.
2. Pour about 1/3 cup of vegetable oil into the jar. When
everything settles, is the oil on top of the water or underneath it?
3. If you want, add one drop of food coloring to
the jar. What happens? Is the drop in the oil or in the water? Does the color
spread?
4. Shake salt
on top of the oil while you count slowly to 5. Wow! What happens to the food
coloring? What happens to the salt?
What's Going On?
Why does the oil float on the water?
Oil floats on water because a drop of oil is
lighter than a drop of water the same size. Another way of saying this is to
say that water is denser than oil. Density is a measurement of how much a given
volume of something weighs. Things that are less dense than water will float in
water. Things that are more dense than water will sink.
Even though oil and water are both liquids,
they are what chemists call immiscible liquids. That's a fancy word that means
they don't mix.
What happens when I pour salt on the oil?
Salt is heavier than water, so when you pour
salt on the oil, it sinks to the bottom of the mixture, carrying a blob of oil
with it. In the water, the salt starts to dissolve. As it dissolves, the salt releases
the oil, which floats back up to the top of the water.
This looks like a Lava Lite. How does a
Lava Lite work?
Like your oil and water, the "lava" in a Lava Lite doesn't mix with the liquid that surrounds it. When it's cool, the "lava" is a little bit denser than the liquid surrounding it. When the "lava" rests on the bottom of the Lava Lite, the light bulb in the lamp warms it up. As it warms up, the "lava" expands a little. When it expands, the "lava" stays the same weight but it takes up more space-so it's less dense. When it's warm enough, the "lava" is less dense than the surrounding liquid, and so it rises up to the top to float. At the top of the lamp, it cools down, becomes more dense, and sinks once again. This cycle repeats over and over as the "lava" warms up and rises, then cools down and sinks.
http://www.exploratorium.edu