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"Stewart Smith" writes:
Here's an interesting aside: Is this the beginnings of a Freeze Ray device? No, it most certainly is =NOT=. Molecules Knocked Cold --------------------------------------------------------------------------- Chemists have long used supersonic gas expansions to create beams of molecules that are "cold" in the sense that the molecules are in low vibrational and rotational states and do not undergo collisions. However, translational motion of the molecules still makes them "hot" in the laboratory frame of reference, Like most press-releases, the above is oversimplified and rather misleading. Please note that the author has used a perverse definition of "hot," namely, is treating coherent translational motion of the stream _AS IF_ it were "random" thermal motion --- which it most definitely is =NOT= !!! The kinetic temperature of a gas is defined in terms the "random" component of motion left over once the _average_ motion of the molecules has been subtracted, i.e., it is defined relative to the _MEAN REST FRAME_ of a parcel of gas. Treating the "bulk" motion _AS IF_ it were "heat" only gets one into trouble, both conceptually and physically. I will give the author "partial credit" in recognizing this conceptual inaccuracy by putting "scare quotes" around "hot" --- but it would have been =MUCH= better if the author had simply =NOT= made this incorrect and conceptually misleading statement _AT ALL_, since it adds nothing of value to the article. -- Gordon D. Pusch perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;' |
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