Correct me if I am wrong but as far as I know, force is generally defined in three ways ways:(adsbygoogle = window.adsbygoogle || []).push({});

1) [tex] F = \frac{d p}{d t} [/tex]

2) [tex] F = m\dot v [/tex]

3) [tex] F = ma [/tex]

This is all well in good usually...until the case arises when mass is variable.

Then two contradictory cases arise:

If we take definition 1...we get

1) [tex] F + u \frac{dm}{dt} = m\frac{dv}{dt} [/tex]

If we take definition 2 we defined the quantity [tex] u \frac{dm}{dt} [/tex] as thrust and part of force and thus

we get [tex] F= u \frac{dm}{dt} +\cdots =ma =m \frac{dv}{dt} [/tex]

Am I missing something here?

Thanks.

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# Force is ill-defined? contradictory definitions?

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