Re: [Phys-L] definition of "power"

[John Denker <jsd@av8n.com>]

On 12/01/2014 01:23 PM, Richard Tarara wrote:

> > Really, you need to be careful in every instance to be very clear.

1) That's excellent advice.

 Different people define power differently.  This horse escaped
 from the barn a long time ago.  For the foreseeable future, the
 R.T. approach seems like the only game in town.

 I've been known to use long-winded expressions such as "F dot v
 mechanical power" and "I dot V electrical power".

On 12/02/2014 10:59 AM, Carl Mungan wrote:
> How about defining power as rate of converting energy from one form
> to another? This could be an internal conversion (burn chemical
> energy of gasoline to get kinetic energy of motion of a car) or an
> external transfer (in the form of work, heat, and/or mass transfer
> from one object or system to another). I'm somewhat undecided about
> whether a transfer of energy without a change in form should count
> (eg. the cue ball hits the 8 ball elastically) but I suppose it could
> so one doesn't have to worry too much about what one means by the
> vague term "forms." Just consider any measurable change in a a system
> to involve energy and hence power.

2) YMMV, but if you want to know my personal preferences, the
 case that has me conflicted is advection.  For example, suppose
 there is a small leak in the gas tank of a car.  Overnight a
 small amount of fuel leaked out.  Is that "power"?

 To say the same thing again, consider the equation:
      dE = F dX + T dS + advection

 If you leave out the advection term, I am perfectly happy
 to let the rest of dE/dt be power, i.e. mechanical power
 plus thermal power.  Advected power seems weird to me.
 I could probably be persuaded either way.

3) I'm not sure I care.  See item (1).  I've pretty much written
 off this word as one of those supposedly "technical" terms
 without any clear meaning.  It's nowhere near being the worst
 offender in this category.
   https://www.av8n.com/physics/weird-terminology.htm