We just wrapped up our first week of classes for the new semester here at Texas A&M. One of the two classes I’m taking this semester is classical mechanics. It’s basically Newton’s three laws wrapped up in the much prettier package of Lagrangians. At first I didn’t think this would offer much to write about physics-wise this semester, but I’m quickly finding out I was wrong. Here are two examples.
The Wine Glass Resonator Gyroscope
After checking out John Blyler’s recent post on MEMS, I did a little research. First off, I think it’s just flat out cool you can buy a gyroscope on a chip now. I had no idea. Things became even more interesting when I found out that one of the popular MEMS gyroscope designs is based on fundamental physics research done in 1890 by G.H. Bryan. Bryan like many an ardent wine drinker had noticed that the tone of the sound made by a resonating crystal wine glass varied if it was moved, rotated, or spun. He worked out some of the basic equations that described the change in tone and unknowingly set a research path in motion that would result in the MEMS wine glass resonator gyroscope a hundred years or so later.
GPS Without Satellites
One of the topics we’ll be discussing in classical mechanics this semester is the Coriolis force. This force is what’s known as a fictitious force and is responsible for things like the circular motion of hurricanes. It’s called fictitious because it’s not a result of one of the four basic forces like gravity or electromagnetism. Instead, it results from the spinning motion of the earth. In any event, it’s fairly basic and is covered rather extensively in undergraduate physics classes.
Here’s the kind of cool part they don’t tell you in undergraduate physics though. In 1915, Arthur Compton, who would later go on to discover Compton scattering, built a global positioning system that allowed him to determine the position of his laboratory to within a few tenths of degree of latitude and longitude. He was able to do this without taking any observations outside and well before satellites were available, much less satellite based positioning systems. Compton’s system consisted only of a circular glass tube filled with water. When the tube was rotated 180 degrees around its diameter the fluid inside began to rotate with respect to the tube due to the Coriolis force. By measuring the rate of rotation of the fluid, Compton was able to work out the magnitude of the Coriolis force at his location, and hence the position of his location on the surface of the Earth. You can read more about it in one of the original Scientific American articles on the apparatus.