Same egg. Same glass. One sinks. One floats. Nothing about the egg changed — but the water is keeping a secret.

Floating is about density — how much mass is packed into a given space. A raw egg is slightly denser than fresh water, so when you drop it in, the water can't push back hard enough to support it. It sinks.

Dissolve salt into the water and something quiet happens. You're adding mass without adding much volume — the water gets heavier without getting much bigger. Its density creeps upward. And as density increases, so does the force the water pushes back with — what scientists call buoyancy.

Add enough salt and the water becomes denser than the egg. Now the push-back force is greater than the egg's weight — and up it goes. The egg didn't change. You changed the rules.

Did you notice the egg seems to float at a very specific level rather than just bobbing on top? It's finding its exact density match — the point where the push-back force equals its weight precisely. Move it higher and it sinks back. Push it lower and it rises again.

You can see the same average density principle doing something even more counterintuitive with an orange in [The Life Jacket], and watch salt change a potato's fate entirely in [Sink or Float?].

What would happen if you made a glass of very salty water and carefully poured fresh water on top — could you get the egg to float perfectly in the middle, suspended between two layers? 

Find out in The Crazy Scientist Lab.