Plane truth. (Letters).
DAVID BUMP, FLUSHING, MICH.
The sentence about the wall reminds me of a similar gaffe that The New York Times made early last century: It criticized Robert Goddard's claim that a rocket could travel in a vacuum because, the reporter said, there was no air for the rocket to push against. Similarly, the force needed to make the laser plane fly needs only to act on the plane itself.
DOUGLAS WARSHOW, ANN ARBOR, MICH.
According to Takashi Yabe of the Tokyo Institute of Technology, the laser vaporizes some of the aluminum and some of the water, creating an explosion and forward thrust. But that's not the whole story. In other experiments, the scientists used a layer of transparent acryl plastic instead of a water droplet. The plane took off fastest when the acryl layer was very thick. In that instance, the explosion sent the plane flying, but the massive plastic block remained stationary. Says Yabe, that finding indicates that propulsion of the plane also results from the overlying substance (either acryl or water) acting as a wall that contains the explosion.--P. WEISS
|Printer friendly Cite/link Email Feedback|
|Article Type:||Letter to the Editor|
|Date:||Sep 14, 2002|
|Previous Article:||Tracks in the Sea: Matthew Fontaine Maury and the Mapping of the Oceans.|
|Next Article:||Howling good time. (Letters).|