My Oceanography students always loved a good science demo. This one is easy to do, inexpensive, and it’s also interesting. Plus you and your family get to learn about the density of seawater.
Materials you’ll need:
- One large clear glass and a second smaller glass
- A boiled egg
- A spoon
- Two different colors of food coloring (optional)
Start by adding water to the large clear glass until it’s just a little bit more than halfway full. Then add salt to the water and stir until the salt dissolves. This demo works better with plenty of salt. Then choose one of your food colors and add it to the salty water and stir until well mixed.
Then place the boiled egg in the saltwater. Saltwater is denser than an egg, which means the egg will float. If your egg doesn’t float, you have to remove it from the glass of saltwater and add more salt. Place the egg back into the glass of saltwater and let it float.
Then add some fresh water to your second glass, and add a different food color to that fresh water. Stir until mixed.
Here comes the amazing part. It’s a bit tricky, but you’re going to slowly pour the fresh water into the same glass that has the saltwater and the egg. In order to pour gently and delicately, you’ll hold the spoon face down and carefully let the fresh water run onto the back of the spoon and into the glass. Don’t worry, it’s not that difficult.
If you did this correctly, the fresh water will remain floating at the top of the glass, the saltwater will stay at the bottom and the egg will float in the middle between the two different waters. It will look cool!
This demo works because the fresh water is less dense than saltwater. The two types of different salinity water will not mix. The egg floats on the saltwater because it’s less dense than saltwater. But the egg is denser than the freshwater, so it will float in the middle of the glass looking cool. The scientific term for this is “density stratification.”
Earth’s ocean is also density stratified, which means that the fresher less dense seawater tends to stay at the sea surface while the denser saltier seawater tends to stay near the seafloor.
Oh, and by the way, you can eat the egg when you’re done.
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