p.17

Note that if a particle is constrained to the surface and  that is itself

moving in time, the force of constraint is instantaneously perpendicular to

the surface and the work during a virtual displacement is still zero even

though the work during an actual displacement in the time dt does not

necessarily vanish.


疑問

  1. 第一句是在說質點被限制在一個本身會移動的面上嗎？
     這樣跟假設點在面上移動有什麼不一樣呢？

  2.既然力都垂直於表面,那為什麼actual displacement 中的work有可能不為0呢?

--
※ 發信站: 批踢踢實業坊(ptt.cc) 
◆ From: 61.230.84.10