RAPID CITY, S.D. (KOTA) – Each week, we bring you a quick and easy experiment you can do at home to explore a concept in science.
This week, we look at mass and density using oranges.
The orange with more mass floats, while the orange with less mass sinks! Why?
The answer has to do with density. How you can explain this to your kids depends on how old they are.
For younger kids, compare the peel of the orange to a life jacket. When a person puts on a life jacket, they are adding mass to their overall body, but it helps them float.
That’s because density depends on a combination of mass and volume:
ρ is a symbol from the Greek alphabet, rho, and in this equation represents density. m represents the mass of the object, and V represents its volume. That means, an object’s density isn’t just about how heavy it is – it’s how heavy it is per unit of space or volume.
The orange with the peel on it has more mass, but it is also bigger. The peel is filled with air pockets, which means it doesn’t have a lot of mass compared to its volume. It lowers the overall density of the whole orange, enough that it floats in water!
Even though the peeled orange has less mass, it’s concentrated in a smaller volume, giving it more density than the unpeeled orange.
Something less dense than water will float, while something more dense will sink. That means an orange with its peel is less dense than water, while a peeled orange is more dense.
If your child is interested in taking the experiment further, salt can help.
When salt is dissolved in water, it increases the water’s density. This means, with the right amount of salt, both oranges will float in water. Challenge your child to add salt slowly and see what happens – if you can get the density of the water and orange equal, it will hover in the water!
The library can be a great place to take your kids to learn more about density and other science topics, especially if you’re not confident in your ability to explain it. Just ask a librarian what topic you want to know more about. Plus, as we hit the heat of summer, it’s air conditioned!
If you do this experiment at home, we’d love to see and feature it! Submit photos and videos here.
See a spelling or grammatical error in our story? Please click here to report it.
Do you have a photo or video of a breaking news story? Send it to us here with a brief description.
Copyright 2026 KOTA. All rights reserved.