※ 引述《fscy (2001太空漫游)》之铭言： : 陈正益写的这篇文章确实是问题很多, 相信很多人都注意到了. : 很多段落的内容都有问题. 我想最大的根源就是来自於所谓的 : 真空理论. : 第118页 任何在大气中移动的物体都会在他身後不断造成短 : 暂的真空,也许短暂到只有千分之一秒.... : 我不知道哪一份科学文献有提及这样的描述, 特别是在流体力学 : 的书籍里. 至少我还没看到有使用"真空"的概念来解释或描述流 : 场中流体复杂行为的书籍或网站. 可能不是指真空而是指球面上的气流没有turbulence 或是说陈正益所写的问题在於--你感觉不到有风吹并不表示空气不存在 虽然硕士班毕业前我一直是念物理的, 但没修过流体力学 :P 所以先把之前看到的post出来 但里面并不是谈大气中移动物体的身後事 只是刚开始提到球的运动 希望没有作过度的引申 如果post是太trivial的东西 不要见怪 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 这本是台湾翻的"牛顿打棒球" 版上有很多人一定都看过了 Robert K. Adair is an emeritus physics professor from Yale University and a member of National Academy of Sciences (类似於台湾的中研院院士). 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. --

※ 发信站: 批踢踢实业坊(ptt.cc) ◆ From: 169.237.17.64 ※ 编辑: MyDice 来自: 169.237.16.132 (01/09 06:16)