推 okdyolka:瞭解了 感謝你解開我的困惑 :D 09/26 03:10
※ 引述《okdyolka (沒事多喝水)》之銘言：
: : : 有個迷思問題
: : : 火箭A騰空飛起 推力正好與重力相抵消 定在原點不動
: : : 火箭B也是騰空飛起 推力正好與重力相抵消 但有一個很小的向上初速 往上做等速運動
: : : --
: : : ◆ 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
: 那麼不也可以說重力對火箭B是做負功
: 重力的負功 與 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.
:
: 重力的負功 火箭的正功 與 增加的重力位能 這三者該如何完整的解釋在一起?
:
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: ※ 發信站: 批踢踢實業坊(ptt.cc)
: ◆ From: 123.204.148.124
: 推 ntust661:記得，等速移動不做功，管你是上下移動還是左右移動 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.
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◆ From: 112.104.98.146