November 2005 NEMES Meeting


PB030098.JPG (73692 bytes)  Errol Groff brought several buckets of drill and end mils that were surplus to needs at Ellis Tech and they were quickly claimed by a number of different members.

PB030099.JPG (61526 bytes)  This small machine was built by Earl Riche of NH for bending sapphire rods.  

PB030100.JPG (75007 bytes)   On the right is  Dr. Jim Philips.  The write up below was in the November Gazette and is included here since I understood almost none of Jim's talk other than the fact that he is measuring VERY small forces of nature.

PB030102.JPG (67942 bytes)  

From the November Gazette:

Also, we have invited Dr. Jim Phillips to speak at the next meeting. He is a researcher at the Harvard-Smithsonial Center for Astrophysics. His research focuses on validating one of the precepts of the Theory of Relativity related to the measurement of the gravitational constant.

In his lab he has constructed an apparatus to do this measurement which is largely mechanical with some optical components. It is an interesting device which bounces a steel cylinder vertically on rails. The throw of the cylinder is on the order of 2 meters and when it reaches the bottom of the throw it lands on the middle of a steel cable. The cable is attached on both ends to large automotive torsion bars which store the energy and return it to the next bounce, less some loss. Currently, the loss is on the order of 25%.

Within the cylinder are some optical components that are mounted on 2 masses. In operation, a laser is pointed into the bottom of the cylinder as it bounces. It bounces and gives up a gravity measurement every 1.3s. 

The interference patterns generated on the laser beam allow the measurement of the gravitation constant to one part in 10^-13th. Jim would like to improve this accuracy figure but is limited by the noise generated in the ball bearings that attach the payload to the rail. Replacing the ball bearings with air rails would likely improve this figure but it would be expensive. Jim is looking for lower cost alternatives to the metal fabrication of the air rails. Tolerances need to be on the order of one thousandth.

During his presentation Jim will describe the apparatus and show pictures of it. Then he will talk about how the air rail system should be constructed. A significant portion of his time will be given to question and answers.

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