Problem with Newtons second law

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Discussion Overview

The discussion revolves around the interpretation of Newton's second law, particularly the equation F = m * dv/dt + v * dm/dt. Participants explore the implications of this equation in non-relativistic contexts, questioning how applied force can affect an object's mass.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant states that in the non-relativistic case, the applied force does not change the object's mass, suggesting that the second term is zero.
  • Another participant provides a practical example of how the mass of a vehicle decreases as fuel is burnt, implying that mass can change under certain conditions.
  • A later reply reiterates the original problem, emphasizing that the equation defines force in terms of observable effects and notes that there are multiple definitions of force, including F = ma.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the second term in the equation, with some asserting that mass does not change in non-relativistic scenarios while others provide examples where mass changes. The discussion remains unresolved regarding the interpretation of force and mass in this context.

Contextual Notes

The discussion highlights the dependence on definitions of force and the conditions under which mass may change, indicating that assumptions about non-relativistic cases may not be universally agreed upon.

Physonic
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hello!

here's my problem:
Newtons second law implies: F=m*dv/dt+v*dm/dt
first part of the equation says if I act on the object then it's reaction will be acceleration, but the second part says if act on the object it will cause changes in object's mass.
In case where I'm dealing with non relativistic case how applied force can change object's mass?

thank you!
 
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In the non-relativistic case the applied force doesn't change the object's mass, so the second term is zero.
 
A practical example is how the mass of a vehicle decreases as fuel is burnt.
 
Physonic said:
here's my problem:
Newtons second law implies: F=m*dv/dt+v*dm/dt
first part of the equation says if I act on the object then it's reaction will be acceleration, but the second part says if act on the object it will cause changes in object's mass.
In case where I'm dealing with non relativistic case how applied force can change object's mass?
It's the other way around. F=dp/dt=m*dv/dt+v*dm/dt is one definition of force. This equation is not saying what forces do, it is giving a definition of what a force is in terms of observable effects. Both of those terms on the right hand side are observable effects. There are other definitions of force, by the way. Some prefer F=ma as definitional, for example.
 

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