Why do we float in the Great Salt Lake?

One thing I love about homeschooling is the ability to mix subjects together. In this case, we mixed some science lessons with some geography lessons. As part of our Utah unit, we learned all about the Great Salt Lake, and that, of course, led us to a Great Salt Lake experiment. How many teaspoons of salt does it take to make an egg float?

Supplies for the Great Salt Lake experiment

egg, salt, cup, water, teaspoon, other small items, printable (available to subscribers)

How many tablespoons of salt does it take to make an egg float?

This is pretty straightforward to complete, just be aware you might get wet in the whole process.

1. Fill 3 cups partially full of water. Then find a raw egg (very important, as cooking changes the buoyancy), a small plastic toy, and one other item.

2. Put each of your items in the cup and see what happens. Do they sink or float? This would be a great time to talk about buoyancy, and why items sink or float.

3.  Start adding teaspoons of salt to each cup. I set up the chart to measure at multiples of 5. So at 5 teaspoons check again how the items are floating in the water.

4. As you add the salt, check occasionally to see how the items do at floating. When your items finally start floating make sure to record the results. Neither our plastic man nor the button we chose ended up floating. I was rather surprised by the plastic man.

Why does this work?

Saltwater is denser than freshwater, so when you add salt to the water, you are making the water denser. The denser water is able to hold the eggs up.

My experiment didn’t work what happened?

Way back when the kids were little we tried the eggs floating in salt water experiment and started out trying the experiment with fresh water.

Our eggs floated.

I was flabbergasted and was trying to figure out what I’d done wrong. I hadn’t cooked the eggs, and there was no reason I could tell for it to not work.

Then I did some searching. The reason the egg floats in salt water is because there is a small air bubble in the egg. As eggs “grow stale” (not the right term, but the best I can think of), the air bubble gets bigger. This is actually a recommended method to find out if the eggs you are using are fresh because fresh eggs sink in water.

And now you know why your egg might be floating in fresh water.

More geography science experiments

Hmph, I guess I need to get busy adding in some more geography-inspired science lessons, I’ve got a few, but they’re not showing up, sadness….

• Mount Saint Helen (Washington)
• Baby peanut in the plant (Georgia)