Problem with Newtons second law

[Physonic]

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!

 

[phyzguy]

In the non-relativistic case the applied force doesn't change the object's mass, so the second term is zero.

 

[Dr Lots-o'watts]

A practical example is how the mass of a vehicle decreases as fuel is burnt.

 

[D H]

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.

 

[sardar]

Hello,

Thank you for bringing up this interesting question. It is true that Newton's second law states that the net force acting on an object is directly proportional to its acceleration, but the second part of the equation, which involves changes in mass, can be confusing. Let me try to explain it in more detail.

In non-relativistic cases, the mass of an object is considered constant. This means that the mass of the object does not change with time. However, if an object is moving at high speeds close to the speed of light, then the mass of the object can change due to relativistic effects. But in most everyday situations, we can assume that the mass of an object is constant.

So, how can the second part of the equation, which involves changes in mass, be explained in non-relativistic cases? Well, it is important to understand that the mass being referred to in this equation is the "inertial mass" of the object, which is a measure of its resistance to changes in motion. This is different from the "gravitational mass" which is a measure of the object's gravitational attraction to other objects.

When an object is being acted upon by a force, it experiences acceleration and therefore, its velocity changes. This means that its inertial mass also changes, as it takes more force to accelerate a heavier object. This change in inertial mass is very small and is not noticeable in most everyday situations. However, it is still a factor that needs to be considered in the equation.

I hope this helps to clarify the second part of Newton's second law and its relation to changes in mass. It is important to remember that this equation is a simplified representation of the relationship between force, mass, and acceleration, and there are more complex equations that take into account relativistic effects. But for most everyday situations, this equation is sufficient to explain the relationship between force and acceleration.

Thank you for your question and keep exploring the fascinating world of science!