Sometimes when we talk about 2 people who don’t get along, we might say they are like oil and water. We mean they don’t mix well together. Have you ever tried to mix oil and water? Even if you stir or shake the solution, the oil and water eventually separate.

Have you thought about why oil and water don’t mix? It’s all related to a concept called density.

The Background Matters

Matter is what makes up a substance or object. It’s anything we can touch, feel, or see. The wind, your shirt, a bird, or lemonade are all types of matter. Matter exists in 4 states- solid, liquid, gas, and a special, charged gas called plasma. Matter is made of atoms and molecules that have energy; how quickly those atoms move around is based on its state. A solid has the least amount of energy; its atoms move slowly. A liquid’s atoms move a bit more rapidly. A gas has the most energy; its atoms fly about speedily, bouncing off each other and the sides of its container.

Every state of matter follows the same principles meaning they act according to consistent properties. For example, we know we can pour a liquid. It’s one of the properties that make it a liquid! Solids, on the other hand, don’t pour. We can observe these consistent properties repeatedly, and they’ll behave the same every time.

What is Density?

All matter mass and density. Mass is how much matter is packed into an object/substance. We calculate mass in grams, pounds, and ounces. Density is how tightly packed that matter is packed into a certain volume.

Let’s say we take two boxes of the same size and pack one with feathers and the other with gold bars. The box of gold bars has more mass. In addition, the box of gold bars has more matter packed into the box’s space; it also has more density. If you spread out your gold bars over several boxes, the mass of the bars would stay the same, but the density would decrease.

What Does Matter & Density Have to Do with Oil and Water?

After attempting to mix oil and water, if you set it aside, you’ll notice something interesting.  The oil moves to the top of the glass while the water moves to the bottom.  The water has more density than the oil. It happens every time.  You can count on it.

Density helps us determine why rafts or boats float, why a hot air balloon rises, and why a rock sinks when you throw it into the pond. Scientists study densities of different elements or molecules to determine how they interact with other substances or how they will behave when their state changes. If we didn’t know about densities, we would not know why it’s important to learn to swim or why a pool noodle floats, but a brick does not.

God Made Water Special

When most substances freeze, their solid form is more dense than their liquid form. Their molecules become more tightly packed together, and frozen form sinks in their liquid. However, God made water unique! Water in its frozen form is less dense than water in its liquid form. Picture what happens in the winter when water freezes on lakes and ponds. That frozen layer of ice doesn’t sink! If it did, it could kill the fish and other creatures below. Instead, God created water that expands when it freezes, giving it less density than its liquid. The ice creates a layer of insulation for the life underneath. Amazing!

Time to See it in Action – Let’s Build a Density Tower!

There is a way to compare the densities of different materials using common household items. Use the link below for the lab instructions and form to record your results. Note that you will want to add each to your glass slowly and carefully, placing them gently into your glass. Don’t stir or shake them.

One thing we can be sure of, God created matter with special characteristics that are consistent and trustworthy. While people can learn to get along and treat one another with kindness, oil and water will never mix!

Like this experiment? You can find this and more like it in our series, The Mystery of Science!