Re: 12月號HIT雜誌所談的變化球理論

[MyDice (Laser Beam Focus)]

※ 引述《fscy (2001太空漫遊)》之銘言：
: 陳正益寫的這篇文章確實是問題很多, 相信很多人都注意到了.
: 很多段落的內容都有問題. 我想最大的根源就是來自於所謂的
: 真空理論.
: 第118頁   任何在大氣中移動的物體都會在他身後不斷造成短
:           暫的真空,也許短暫到只有千分之一秒....
: 我不知道哪一份科學文獻有提及這樣的描述, 特別是在流體力學
: 的書籍裡. 至少我還沒看到有使用"真空"的概念來解釋或描述流
: 場中流體複雜行為的書籍或網站.
可能不是指真空而是指球面上的氣流沒有turbulence
或是說陳正益所寫的問題在於--你感覺不到有風吹並不表示空氣不存在

雖然碩士班畢業前我一直是念物理的, 但沒修過流體力學 :P
所以先把之前看到的post出來  但裡面並不是談大氣中移動物體的身後事
只是剛開始提到球的運動  希望沒有作過度的引申
如果post是太trivial的東西  不要見怪 XD

The most interesting actions in the game of baseball take place
when velocities of the ball range from a few miles per hour(and Reynolds
numbers of 10,000) to values near 120 mph(and Reynolds numbers near 20,000).
For velocities in that range below about 50mp, the flow of the air around
the ball is rather smooth, though trailing vortices are generated. This
airflow does not actually reach the surface where there is a quiet boundary
layer. A very small insect sitting on the moving ball would feel no breeze
at all. At velocities about 200mph the flow penetrates the boundary layer(the
insect would have to hold on very tightly to avoid being blown off) and the
air at the boundary-and trailing behind the ball-is quite turbulent......
for balls traveling at the transition velocities between 50mph and 120mph,
the flow can be smooth or turbulent, depending on the detailed character of
the surface of the ball and its motion.

from "The Physics of Baseball" by Robert K. Adair

這本是台灣翻的"牛頓打棒球"  版上有很多人一定都看過了
Robert K. Adair is an emeritus physics professor from Yale University and a
member of National Academy of Sciences (類似於台灣的中研院院士). His research
is concerned with the properties of the elementary particles and forces of the
universe. He has ever been named "Physicist to National League" in 1987.

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◆ From: 169.237.17.64
→ pig:creeping flow嗎？ (sorry我忘光光了^^")
→ MyDice:不知creeping flow希望有念機械之類的人
※ 編輯: MyDice          來自: 169.237.16.132       (01/09 06:16)
→ lordcolus:我是念機械的 不過我留力被當 ￣▽￣|||
→ bluepegasus:creeping flow就是指很黏度很大..速度慢