system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do lava lamps work?
gpt
Wax has a relatively low melting point, enough that when it gets near the light at the bottom, it melts. The melted wax is less dense than the liquid around it, so it rises. As it gets away from the light, it cools, condensing back  into a solid. The solid is now denser than the liquid around it, so it sinks. Rinse and repeat.