Here is the fifth video in Engineer Guy Series #4. The element of the week is cesium, as in “cesium fountain atomic clock.” Watching it, my jaw was on the floor by 0:20, as Bill opens by showing off the Symmetricom CSAC, which is the world’s first fully functional chip-scale atomic clock. It’s about the size of a quarter. Bill then segues, thusly, into the general theory of atomic clocks: “I’ll start with Jell-O,” he says, producing a quivering green mound of it. And it just gets better from there, wrapping up with a clear, concise explanation of the Global Positioning System, and why it couldn’t work, at all, without the use of atomic clocks. [Thanks, Bill!]

Update:  Woops!  Sorry for the dupe, folks!  Engineer Guy videos always get us really excited.

How a cesium fountain atomic clock works