Jhon Hayman

Lava lamps were very popular back in the groovy 1960s! Many people still have them at home today.

Most lamps light up a room. But lava lamps are mainly just fun to look at. They have coloured wax globules floating around in a transparent liquid.

Lava lamps are also a “groovy” way of seeing physics and chemistry principles in action.

To understand how lava lamps work, you have to understand Kinetic Molecular Theory. It states that all matter is made up of molecules that are always moving. These molecules have kinetic energy. The amount of energy depends on the temperature. When it’s hotter, molecules have more energy. And when they have more energy, they move faster. There are three most common states of matter.

The molecules in solids have the least energy. That means they move more slowly than molecules in liquids and gases.

The molecules in gases have the most energy of all. They move the fastest.

Kinetic molecular theory can help you understand density. Density refers to how much matter there is in a given volume of space.

Have you ever thrown a coin into a fountain or a rock into a pond? You probably noticed that these objects sink in water. And you’ve probably noticed that other objects, like twigs, float on water. The objects that are denser than water sink. And the objects that are less dense than water float.

But what does this have to do with lava lamps? Remember the globules - let’s call them “globs” for short - that float around? At room temperature, the globs are a bit denser than the surrounding liquid. That’s why they sit at the bottom of the lamp. But when you turn the lamp on, the globs heat up. The molecules move faster. The globs become less dense than the surrounding liquid. They rise and start to float around!

So why don’t the globs of wax in a lava lamp mix with the surrounding liquid?

Think about chocolate syrup and milk. They’re miscible liquids. That means they can mix to form a homogeneous mixture.  The chocolate syrup mixes completely with the milk to form yummy chocolate milk!

But some liquids are immiscible. They don’t mix with each other. It all depends on the force of attraction between the molecules in the two liquids.

For example, what happens when you try to mix oil and vinegar - like in a salad dressing? The molecules in the vinegar are more attracted to each other than to the molecules in oil. The molecules in oil are more attracted to each other than to the molecules in the vinegar. No matter how much you shake or stir your dressing, they will never stay mixed together.

But chocolate syrup molecules are attracted to milk molecules. And milk molecules are attracted to chocolate syrup molecules. That’s why you get chocolate milk and not a lava lamp in a glass!

Each immiscible liquid is called a phase. A mixture with two immiscible liquids is called a biphasic mixture. A mixture with more than two immiscible liquids is called a multiphasic mixture.

When you watch the globs float around in a lava lamp, you’re looking at a biphasic mixture!

One of the most interesting features of a lava lamp is the way that the globs float around. But why does this happen? You know that the globs are less dense than the surrounding liquid. And you know that the globs and the liquid are immiscible. So why don’t the globs just rise to the top of the lamp and stay there?

Well, lava lamps are designed so that the temperature at the top is a bit cooler than at the bottom. And what happens to molecules when they cool down? That’s right! They lose energy and move closer together. So when a glob reaches the top of the lava lamp, it contracts. It becomes denser than the surrounding liquid and begins to sink. When it reaches the bottom, the whole cycle repeats!

A lava lamp is an example of a convection current. Convection currents cause liquids and gases to rise and fall because of changes in their density. There are convection currents all around you, even in the Earth’s crust!

You can build your own lava lamp in your classroom or at home! Here’s what you’ll need:

How to make a lava lamp:

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