- #1
semc
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hmm...i was wondering is there any conditions for the use of Newton's second law?
Newton's 2nd Law: Conditions & Application
- Thread starter semc
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Homework Help Overview
The discussion revolves around the conditions for applying Newton's second law, particularly in the context of varying mass systems. Participants explore the implications of using the equation F=dmv/dt compared to the more common F=ma, which assumes constant mass.
Discussion Character
- Conceptual clarification, Assumption checking
Approaches and Questions Raised
- Participants question the conditions necessary for applying Newton's second law, particularly regarding mass variation. There is a discussion about the generality of the equation F=dmv/dt and its application in scenarios where mass is not constant.
Discussion Status
The discussion is active, with participants verifying their understanding of the conditions under which Newton's second law applies. Some have provided insights into the implications of mass variation, while others are exploring specific examples to clarify their thoughts.
Contextual Notes
Participants are considering scenarios involving changing mass, such as a railroad car losing water, and the implications this has on the application of Newton's second law. There is an acknowledgment of the complexity involved in these situations.
- #2
Doc Al
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What do you mean?
- #3
radou
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semc said:
The 'conditions' which imply the usage of an equation are read from the equation itself.
- #4
semc
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i don't reali know how to put it in words but erm...we do not need a varying mass to use F=dmv/dt right?
- #5
Doc Al
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Right. F= d(mv)/dt is more general than F=ma, which assumes a non-varying mass.
- #6
radou
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semc said:
Well, if the mass is not constant, then you have [tex]\vec{F}=\frac{d}{dt}(m\vec{v})=\frac{dm}{dt}\vec{v}+m\frac{d\vec{v}}{dt}[/tex].
- #7
semc
- 364
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Alright i just came across this dumb conditions and i wanted to verify that this is nonsense Thanks
Thanks- #8
OlderDan
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An easy calculus problem, but a tricky physics problem. Suppose there is a railroad car coasting with speed V on a straight horizontal track without any rolling friction. The car is full of water and has initial mass Mo and velocity Vo. As the car rolls, the water in the tank leaks out of a hole in the bottom of the tank at a rate we can assume to be constant (maybe the hole gets a little bigger as the water level drops). So the mass M of the car is changing at a constant rate. The only forces acting on the car are gravity and the normal force, both of which are perpendicular to the motion. What happens to the velocity of the car?radou said: