At-home STEM Activities: Density of Liquids
The Discovery Center’s mission is to inspire every generation to reach for the stars, through engaging, artful and entertaining activities that explore astronomy, aviation, earth and space science. So while were closed and while our visitors are finding the best ways to learn at a distance, we’ll be posting some activities here with the goal of helping to enrich kids’ education at home.
Imagine you’re going on a trip and you need to pack a suitcase. You don’t want to pay extra baggage fees, so you’re trying to fit everything in your carry-on luggage. Let’s say you’re going away for a weekend. Then you only need to pack two day’s worth of clothes, so there’s plenty of room in your suitcase. Now, let’s say you’re going on a week-long trip. You’ll need clothes for seven days, so you need to pack things a little more tightly. If you’re going away for two weeks, you’ll need even more clothes, so you’ll have to pack your bag even tighter. That is to say, you need to pack your bag more densely.
Weekend trip
week-long trip
two week trip
Density is defined as mass divided by volume. In simpler terms, density is how much stuff is in a given space. So with our luggage, the bag packed for two weeks is denser than the bag packed for a weekend, since the volume is the same but the amount of things packed is greater for the longer trip. When we’re talking about density of a liquid, it’s the same idea, but instead of clothes, we’re talking about molecules. Density of a liquid is telling us how closely the molecules are packed together.
Let’s investigate how liquids of different densities interact with each other!
Layered Liquids
Materials:
Honey
Dish soap
Water
Vegetable oil
Rubbing alcohol
Food coloring
A clear container—we’re using a glass jar
Measuring spoons
Small bowls (for mixing colors)
Instructions:
1. For liquids that are the same color, measure out two tablespoons of each. For us, that’s the water, dish soap, and alcohol. Add a drop of food coloring in colors of your choice to each liquid. This will allow you to differentiate your liquids.
2. Slowly and carefully pour each liquid into the jar. If you pour too quickly, the liquids may mix together. Using a spoon can help to gently add each new liquid.
Because each liquid has a different density, they will form layers in your jar. Make a prediction about what the order of the liquids is going to be from top to bottom, and scroll down once you have a hypothesis.
Was this the order you predicted?
Why does this happen?
Each liquid has its own density. Here are the densities of the liquids we used:
Honey, about 1.4 grams/milliliter
Dish soap, about 1.03 g/mL
Water, about 1.0 g/mL
Vegetable oil, about 0.9 g/mL
Rubbing alcohol, about 0.8 g/mL
So the order of the layers corresponds to the density of each liquid. The densest liquid, honey, sits at the bottom, and the least dense liquid, rubbing alcohol, sits at the top.
Take this activity further:
Try different liquids: Add corn syrup, baby oil, or milk to your jar. Where do you think those liquids will be in the stack?
Solid objects have specific densities, too: Try gently dropping small objects into the jar, like a penny, a paper clip, or a marble. What do you think will happen? Will the objects fall all the way to the bottom? What does this tell you about the densities of the objects compared to the liquids?
Change the temperature: Instead of using different liquids, try using one liquid at different temperatures. Fill a cup halfway with cold water and add a couple drops of food coloring. Do the same in another cup with hot water. Slowly pour the hot water into the cold water cup. What do you think will happen?
