- #1
dracobook
- 23
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Correct me if I am wrong but as far as I know, force is generally defined in three ways ways:
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.
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.
Last edited: