Timeline for Why is $F = ma$ at an instant, in variable mass systems? [duplicate]
Current License: CC BY-SA 4.0
8 events
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| Jul 25, 2023 at 8:18 | comment | added | Farcher | The question and most of the answers wrongly assume that ${\bf F}_{\rm ext} = d{\bf v}/dt$ is valid for variable mass systems. | |
| Jul 25, 2023 at 8:10 | history | closed | Farcher newtonian-mechanics Users with the newtonian-mechanics badge or a synonym can single-handedly close newtonian-mechanics questions as duplicates and reopen them as needed. | Duplicate of Second law of Newton for variable mass systems | |
| Jul 24, 2023 at 23:46 | comment | added | Science done right | Exactly! That's why I was confused. But then, I thought, since P is only the momentum of the rocket as a function of time, dP/dt should give us net force force acting on the rocket only, right? | |
| Jul 24, 2023 at 19:13 | answer | added | David White | timeline score: 0 | |
| Jul 24, 2023 at 17:40 | history | edited | Qmechanic♦ | CC BY-SA 4.0 |
added 2 characters in body; edited tags; edited title
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| Jul 24, 2023 at 17:20 | comment | added | garyp | We don't ignore the second term. We just make sure we are applying $d(mv)/dt$ correctly. There are a few ways to show that your suggestion leads to motion not observed in nature, i.e. nonsense. Consider a rocket at constant speed shedding mass in two streams diametrically opposed, and perpendicular to the velocity. There is no net force on the rocket, so the velocity will remain constant. But your equation says that the rocket will slow down. | |
| S Jul 24, 2023 at 16:34 | review | First questions | |||
| Jul 24, 2023 at 17:26 | |||||
| S Jul 24, 2023 at 16:34 | history | asked | Science done right | CC BY-SA 4.0 |