Take students back to the ‘70s with these DIY lava lamps! This science experiment illustrates two scientific concepts - polarity and density - in a fun and simple way. And it will also help you score a few cool points with your students.

Before starting the activity, explain density and polarity to students.

In simple terms, density describes how compact or concentrated an object is. For example, you have a large and a small box, but they both weigh the same. That means the small box has a higher density than the large box because it contains more mass. Density also determines whether an object will float or sink in another substance.

Polarity refers to molecules that are positively charged at one end and negatively charged at the other. It also determines how atoms bond with each other.

Materials:

A tall bottle
Cooking oil (enough to fill up ¾ of the bottle)
Water
Food coloring
Fizzy antacid tablets (such as Alka-Seltzer)
Submersible/waterproof light or flashlight
Glitter (optional)
Salt (optional)

Instructions:

Ask students to fill three-fourths of their bottle with cooking oil. They can fill the remainder with water, but not all the way to the top. They’ll need some room for bubbling.
Have them add a few drops of food coloring.
Leaving the top of the bottle off, let students break up the fizzy tablet and drop it in a bit at a time. Watch what happens to the gas bubbles created and observe the rising droplets of colored water.
Add a submersible light, which will float on top and light downward. Or shine a flashlight up from the outside bottom for a more realistic lava lamp effect.

The Science Behind the Experiment:

To start, the oil stays above the water because it’s lighter, or less dense, than water. And oil and water don’t mix due to “intermolecular polarity.” That basically means that water molecules like to stick together and oil molecules like to stick to together. But they’re not allowed to bond together due to their molecular structure.

Once the tablet was added, it sank to the bottom of the bottle and started dissolving and creating a gas. As the gas bubbles rose, it collected some of the colored water. When the water bubble reached the top, the gas escaped and the water got heavy again and sank. This reaction continues until the tablet is completely dissolved.

You can find this activity and similar science experiments in Banish Boredom: Activities to Do with Kids That You’ll Actually Enjoy.