Zend
發表於 18-2-2009 18:32:12
你肯定係用 F=m(dv/dt)+v(dm/dt) ?
我對你呢個chain rule既由來有點好奇.
【YU】 發表於 18-2-2009 17:17 http://nakuz.com/bbs/images/common/back.gif
New way -.-
dmv = Fdt
but in fact, there are two variables m, v, partial derivatives should be taken
F=dmv/dt= partial dmv/dm . dm/dt + partial dmv/dv . dv/dt
=v.dm/dt+m dv/dt
Puppet
發表於 18-2-2009 22:14:21
你肯定係用 F=m(dv/dt)+v(dm/dt) ?
我對你呢個chain rule既由來有點好奇.
【YU】 發表於 18-2-2009 17:17 http://www.nakuz.com/bbs/images/common/back.gif
F = ma is a special case only wor= =
See see 2nd law la
[S]【YU】
發表於 18-2-2009 23:34:44
F=ma is the general case - - dm/dt is the special case wor
Puppet
發表於 18-2-2009 23:49:32
F=ma is the general case - - dm/dt is the special case wor
【YU】 發表於 18-2-2009 23:34 http://www.nakuz.com/bbs/images/common/back.gif
Newton's 2nd law says what??[]
S!UwlnG
發表於 18-2-2009 23:56:10
14# Puppet
F=ma
無．話可說
發表於 19-2-2009 10:39:02
你肯定係用 F=m(dv/dt)+v(dm/dt) ?
我對你呢個chain rule既由來有點好奇.
【YU】 發表於 18-2-2009 17:17 http://nakuz.com/bbs/images/common/back.gif
我是不是弄錯了甚麼地方 @@?
如有錯誤, 請指正 a_a
Puppet
發表於 19-2-2009 13:49:32
本帖最後由 Puppet 於 19-2-2009 13:54 編輯
15# S!UwlnG
2nd law does not say "F=ma (special case)
just like Avogadro's law does not say "2 mol of a gas occupies 48 dm3. (CE) (special case)"
[S]【YU】
發表於 19-2-2009 15:54:20
F = ma is a special case only wor= =
2nd law does not say "F=ma (special case)
double definitions - -
u mean it is a special case or not ar?
16# 無．話可說
[]只係引式無詳細解釋,想你講清楚d je.
無．話可說
發表於 19-2-2009 17:22:46
double definitions - -
u mean it is a special case or not ar?
16# 無．話可說
[]只係引式無詳細解釋,想你講清楚d je.
【YU】 發表於 19-2-2009 15:54 http://nakuz.com/bbs/images/common/back.gif
oic.. 不過樓上都有人講左了
只是d一d條式only -.-
Puppet
發表於 19-2-2009 18:24:01
本帖最後由 Puppet 於 19-2-2009 18:30 編輯
2d law does not states that: "F=ma."
That means, when we want to tell what 2nd law is, it would be improper to say: "F=ma".
F=ma is only a special case of 2nd law.
c.f. When we want to tell what Avogadro's law is, we won't say: 'Avogadro's law says that: "2 moles of helium occupies 48dm3 at r.t."
c.f. When we want to tell what Faraday's law of electromagnetic induction is, we won't say: "induced e.m.f.=-NA(dB/dt)"
if in doubt, check out what the 2nd law originally says