我想問下有關net force既問題...

Zend

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.
[S]【YU】 發表於 18-2-2009 17:17

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

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.
[S]【YU】 發表於 18-2-2009 17:17

F = ma is a special case only wor= =
See see 2nd law la

[S]【YU】

F=ma is the general case - - dm/dt is the special case wor

Puppet

F=ma is the general case - - dm/dt is the special case wor
[S]【YU】 發表於 18-2-2009 23:34

Newton's 2nd law says what??[[onion_56]]

S!UwlnG

14# Puppet
F=ma

無．話可說

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.
[S]【YU】 發表於 18-2-2009 17:17

我是不是弄錯了甚麼地方 @@?
如有錯誤, 請指正 a_a

Puppet

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】

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
[[tk_21]]只係引式無詳細解釋,想你講清楚d je.

無．話可說

double definitions - -
u mean it is a special case or not ar?

16# 無．話可說  
[[tk_21]]只係引式無詳細解釋,想你講清楚d je.
[S]【YU】 發表於 19-2-2009 15:54

oic.. 不過樓上都有人講左了
只是d一d條式only -.-

Puppet

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