Coffee, water, anti-tank weapons, & nuclear explosions

I was working with a camera development board from Aptina Imaging, and I decided to try to capture a few high-speed videos, and here're the results. The videos were captured at a few hundred frames per second, then slowed down for playback.

The hardware I used is nowhere nearly fast enough to capture the flight of bullets, so I was stuck with the milk-drop variety. There are lots of slow motion videos of milk drops on youtube, so I decided to do something slightly different: drops of coffee falling into clear water. I know, very creative, but the choice of clear water turned out to be good. The video quality isn't good, but hey, I was using a cheap hardware system.

Here's the first video, a drop of coffee into water:



Here's the second video, 2 drops of coffee into water:



Here's the third video, 3 drops of coffee into water. No, just kidding, it's side-view of a drop of coffee into water:



Now the third video is most interesting. Like everyone else, I've seen things falling into water countless times, but that third, side-view video revealed details I've never noticed before.

Basically, when a drop of coffee falls into a glass of water, what happens can be roughly divided into 5 stages:

1. The drop of coffee falls thru the surface of the water, creating a depression on the surface of the water.

2. As the water rush in and fill that depression, a jet of water forms and shoots upward.

3. Apparently different parts of the water jet travel at different speeds, because some water separate from the main body of the jet and forms a small water sphere above it.

4. Everything fall back into the water, waves form.

5. A "coffee ring" forms in the water, expanding slowly and sinking.

The formation of the water jet from the depression on the water surface reminds me of the Munroe effect, the physical phenomenon used by shaped-charge anti-tank weapons to punch thru thick tank amour. And that expanding, sinking coffee ring reminds me of the expanding but rising mushroom cloud following a nuclear explosion.

Now you know how to do weapons research using coffee and water.