First law of this universe

[jbriggs444]

For example, one of my properties is my height, 1.88 meters. When I get in my car and drive from my home to the pickleball court would we say my height moves? I suppose we could, but it's not done.

Height is not conserved. Nor is it usually additive. That makes it less meaningful and less useful to speak about height "moving".

On the other hand, another one of my properties is my mass, 107 kg. Would we say my mass moves when I make that same trip? Unfortunately, many do.

We can and often do speak of a mass flow rate. Mass is conserved and [in common circumstances] localized. We can meaningfully speak of its motion.

If an aircraft is not well balanced it makes sense to speak of moving mass fore or aft. Whether that mass is embodied in passengers, cargo or fuel is less relevant than the fact that some mass needs to be relocated.

Authors often write, and instructors often speak, of a mass hanging from a spring, for example. But that's a bad habit.

I see what you are saying. There is a lack of precision in speaking there. Reinforcing a category error.

But even if we take the strict view that mass is a property of an object rather than an independent entity in its own right, I maintain that if a property is both conserved and localized it can make good sense to speak of its motion.

 

[Herman Trivilino]

Height is not conserved.

Huhh? My height hasn't changed in decades whereas my mass has significantly. Although not during the trip I mentioned.

 

[jbriggs444]

Huhh? My height hasn't changed in decades whereas my mass has significantly. Although not during the trip I mentioned.

Global conservation of mass is a feature of classical mechanics.
Local conservation of stress energy is a feature of general relativity.

I am currently at an age where my height is almost certainly decreasing over time.