Transcript:

Remember the story of that smart crow who finds a little bit of water in a big jar, and then he goes and searches for some pebbles and then drops them into the jar, and then magically, the water rises all the way to the top, and he can drink it. Let's see if that story is true.

So, this is a glass that is one-third full of water. I'm going to add some pebbles to it. You see, I added a lot of pebbles, but there is no way the water is coming up all the way to the top of the glass. So you can see, as I put more and more pebbles in that glass of water, it would only rise up to a certain level.

The theoretical minimum water that is needed is 25% of the volume of the glass. This is the theoretical minimum because close-packed spheres will have a void fraction of around 25%. But in actuality, randomly shaped pebbles will pack less efficiently. So you need at least 40% of the glass to be full before dropping pebbles will bring the water all the way to the top of the glass.

Now you know.