## Thursday, November 13, 2014

### Rosetta Mission and Noodle Bridges

A couple of unrelated engineering feats occurred yesterday, and I'd like to address them.

First off, the European Space Agency (ESA) succeeded in landing a probe (Philae) on a comet (67P) for the first time in history.  The level of difficulty of accomplishing such a thing is truly off the scale.

A comet is tiny, 'celestially speaking'.  The mass of 67P is about 10^13 kg.  That's a one with 13 zeros attached to it.  But that makes its mass about 100,000,000,000 times lower than that of a typical planet.  Another aspect that makes docking with such a body tricky is its irregular, peanut-like shape.  It is far from a sphere (largest dimension about 5 km, and smallest about 2 km).  Still, regardless of where you land on this comet, the surface gravity is on the order of 0.001 m/s/s (about one ten-thousandth that of the Earth).  So, if you want to dock, you'd better hang on, because escape velocity is only about 1 m/s (jump, and you now orbit the Sun).

## Wednesday, November 5, 2014

### My Halloween Costume: A Free-Body-Diagram

Last week, on Halloween day, I came to work dressed in a costume...

As you can possibly tell, I was dressed up as a free-body-diagram.  All the forces acting on me were identified by force vectors (large red arrows) at their respective points of application.

I had the gravitational force, mg, acting at my center of mass, and then a reaction load at each foot.  In the picture above, I also posed with a reaction coming from the wall I was leaning against.  Hanging around my neck is a list of assumptions (this costume is valid under the following conditions...).

So, there you have it.  If you were wondering if I'm a nerd, you now have your answer.  I think even my physics teacher colleagues found it slightly nerdy - that speaks volumes.

I got some nice reactions from my students that day, though as I walked through the halls, non-science folks gave me some strange looks.  I spared my family any embarrassment by removing my costume before I returned home.