Why does a homemade lava lamp work?

Answer 1

The inside of a workable lava lamp bottle contains two immiscible liquids. That means they neither will mix or dissolve with each other. One clear liquid fills the bottle. The other liquid is usually a different color and at room temperature can be heavier than the main liquid. In the commercial variety it is a solid at room temperature.

When A light bulb in the base turns on and gets hot, the bottom of the bulb also gets hot as does the colored material at the bottom. As it heats up (If a solid it melts), it expands, becomes less dense, and rises. As it rises to cooler locations, it starts cooling, becomes more dense, starts descending where it gets warmer and starts to rise again. This is similar to a convection current within the liquid.

The colored material will tend to stay together since it dissolves with itself and not with the other liquid. If shaken, the colored materials will disperse into smaller particles but will eventually join together as it dissolves with its own type.

If the two immiscible liquids are of similar density, it will still work as the convection currents within the heated bottle will continue to move things around.

Answer 2

A homemade lava lamp works by creating a colorful display of blobs moving up and down the liquid inside the lamp. This effect is achieved by combining water, oil, and effervescent tablets (such as Alka-Seltzer) in a bottle. The tablets release gas bubbles that attach to the colored water, causing it to rise to the top and then sink back down when the bubbles pop.