A Promethean Thought Experiment

[IggyZ]

Even a very small amount of energy transfer per second, can cause the acceleration of a very large mass to a very high speed, if that transfer continues to occur for a long enough period of time.
In the case of a locomotive and cars, wind resistance would eventually become the limiting factor.
This is because wind resistance increases when the speed of the train increases. The resistance to acceleration against the    inertia of a mass     is a different kind of consideration.  In theory, one can tow a battle ship until is moving very fast (in deep space) by the tug of a thread, if one is patient enough / has enough time to wait.

One could buildup and store energy in the fly wheel.  This can be useful.  On might then
release that energy gradually, or, as some kind of burst of energy.  When the energy is released
as a burst / a large amount at once, this it seems, often confuses experimenters into thinking
more energy has come out of the fly wheel than was put into it.  This confusion it seems is
especially common when these burst occur repetitively as is some times the case in resonating
electromagnetic events.

More to the point here.  If for simplicity, we for the time being ignore friction and some other
kinds of losses, we can look directly at the energy and power transferred or expended in
an electric generator as its conversion to motion via an electric motor.

If an electric generator is able to spin freely, in order to accelerate it, one is only working
against the inertia of the generators rotor.  If an electric generator is able to spin freely,
this is because there is no electrical load upon it (i.e.no electric motor being driven). 

One can eventually give it a very high speed of rotation, given that there is no electrical
load upon it (ignoring friction and so on for now).

The power to weight ratio comes into consideration really, only with the considerations of
1. how       rapidly     accelerations can occur
             i.e.  Does one wish to spend a month of time accelerating a train?
                                                            and
2. when going up hill.

                OK ?

Thanks.

OK? Yes and no...

If I understand you correctly, you are saying a power-to-weight ratio of 12 watt per kg (1.600 KW) is enough to give a 140 tons rotor of a generator a speed of 45 kmh, providing there is no electric load on the generator? Correct?

Don't forces like eddy currents and hysteresis occur simply because the magnetic field of the spinning rotor interacts with the stator of the generator? Isn't this always the case whether or not there is an electric load on the generator?

[Floor]

If I understand you correctly, you are saying a power-to-weight ratio of 12 watt per kg (1.600 KW) is enough to give a 140 tons rotor of a generator a speed of 45 kmh, providing there is no electric load on the generator? Correct?

Yes and no.  Power to weight ratio is not part of the equation except that / unless
the power source is on board.

Don't forces like eddy currents and hysteresis occur simply because the magnetic field of the spinning rotor interacts with the stator of the generator? Isn't this always the case whether or not there is an electric load on the generator?

Only when the generator is of a type which uses permanent magnets.

But then also...
I was speaking in terms of excluding all "losses"  friction, eddy currents and hysteresis,
" magnetic cogging", kinetic energy's converion into unproductive vibrations, others.

[IggyZ]

Yes and no.  Power to weight ratio is not part of the equation except that / unless
the power source is on board.

Only when the generator is of a type which uses permanent magnets.

But then also...
I was speaking in terms of excluding all "losses"  friction, eddy currents and hysteresis,
" magnetic cogging", kinetic energy's converion into unproductive vibrations, others.

Thx Floor.

Why is the power-to-weight ratio not part of the equation except that / unless it is on-board the train?

The generator's rotor I use in my thought experiment uses permanent magnets.

The generator's stator in my thought experiment is iron-less = no cogging.

Friction and vibrations are mechanical losses. Aren't eddy currents and hysteresis losses core, copper or stray losses?

It looks like all the losses you list are all covered by the power flow diagram and the fact I use a permanent magnet generator with an iron-less core in my thought experiment. Thus most of the mechanical input power should be converted into electricity.

[Floor]

@ george1

It's like this

There are commonly two power to weight ratio considerations that are looked at
in this arena (energy and efficiency wise).

1. Energy or power density, as in how much do the electric batteries in an electric
vehicle weigh compared to the number of amp or watt hours they can deliver on
a single charge.  The power source is on board.

2. One seeks the rapid acceleration of, for example a fast automobile. In the U.S.
this is typically judged by the car's ability to accelerate from 0 to 60 miles per hour in
some number of seconds. This is another kind of "efficiency".

The best of conventionally available electric generators are > 98% efficient at
converting mechanical power into electrical power.

  All in all...

This is why I have said that your usage of terms does not make sense / is like
comparing apples to oranges.  i.e. "power-to-weight ratio" in the context in which
you use the phrase.


          P.S.
  It remains that you have not responded to a single one of my questions and
that your topic is just more click bait.

[Floor]

or

Will you please ...

state simply, the basic premise of your "Promethean thought experiment" ?

Question...

Does a flat ended, rotating cylindrical disk with a total mass of 1 kg, while its outer
edge is rotating at a speed of 1 meter per second..
                        posses
as much kinetic energy as does that same object when not rotating, but which is
instead, moving in a straight line of travel, at a speed of 1 meter per second ?

Answer is no.  When moving in a straight line all of the mass is moving at 1 meter per
second.  When rotating, the mass of the object is distributed as moving at speeds of
from zero meters per second to 1 meter per second.
                          From its center (0m/s) to its edge (1m/s).

Is it not ?