作者JohnMash (John)
看板Physics
标题Re: [问题] 做功与否
时间Sat Sep 26 03:07:23 2009
※ 引述《okdyolka (没事多喝水)》之铭言：
: : : 有个迷思问题
: : : 火箭A腾空飞起 推力正好与重力相抵消 定在原点不动
: : : 火箭B也是腾空飞起 推力正好与重力相抵消 但有一个很小的向上初速 往上做等速运动
: : : --
: : : ◆ From: 112.104.50.158
: : For B, push force does positve work
: : but it transforms to gravity potential energy,
: : IRRELEVANT to kinetic energy
:
: 如果如你所言
: 那麽不也可以说重力对火箭B是做负功
: 重力的负功 与 火箭引擎的正功 相互抵消?
This is a basic concept.
push force is an external force.
if you consider gravity as an external force,
then there is no gravity potential.
if you consider gravity as a conservative force in the mechanical system,
then you CANNOT think gravity as an external force.
:
: 重力的负功 火箭的正功 与 增加的重力位能 这三者该如何完整的解释在一起?
:
: --
:
※ 发信站: 批踢踢实业坊(ptt.cc)
: ◆ From: 123.204.148.124
: 推 ntust661:记得，等速移动不做功，管你是上下移动还是左右移动 09/26 02:45
push force does positive work, because displacement is
parallel to push force.
There is NO other external force except push force when gravity
is included in the gravity potential.
--
※ 发信站: 批踢踢实业坊(ptt.cc)
◆ From: 112.104.98.146
1F：推 okdyolka:了解了 感谢你解开我的困惑 :D 09/26 03:10