The potato didn't change. The water did. And that changes everything.

Fresh water has a certain density — a certain amount of stuff packed into every drop. A potato is just a little bit denser than fresh water, so it sinks. Not by much — but enough.

Now dissolve salt into that water. The salt packs extra mass into the same space, making the water heavier without making it much bigger. 

The water's density creeps up... and at some point it overtakes the potato. Suddenly the potato floats.

Did you notice the water looks completely identical in every tube? You can't see the salt. You can't smell it. But the potato knows. It's reading the density of every liquid and responding perfectly every time.

And here's the really wild part — get the mix just right and the potato doesn't sink or float. It just hovers. Perfectly still. Suspended in the middle like it's weightless.

Scientists call that neutral buoyancy — and it's exactly how fish stay at the same depth without swimming, and how submarines dive and surface without using their engines.

A potato just taught you how a submarine works. 

But how does a fish change its depth whenever it wants — without fins, without effort? 

You can see the same density principle at work in [The Imposter] — where a raw egg does exactly what your potato did — and in [Coke Density], where the difference between sugar and artificial sweetener creates a floating surprise with two identical-looking cans.

The answer is one of the cleverest things in nature. Find out in The Crazy Scientist Lab!