analogy in scientific theories

[gusl]

from http://www.repairfaq.org/REPAIR/F_appfaq1.html:

The easiest way to explain basic electrical theory without serious math
is with a hydraulic analogy. This is of the plumbing system in your house:

Water is supplied by a pipe in the street from the municipal water company
or by a ground water pump. The water has a certain pressure trying to
push it through your pipes. With electric circuits, voltage is the analog
to pressure. Current is analogous to flow rate. Resistance is analogous
the difficulty in overcoming narrow or obstructed pipes or partially open
valves.

Intuitively, then, the higher the voltage (pressure), the higher the
current (flow rate). Increase the resistance (partially close a valve or
use a narrower pipe) and for a fixed voltage (constant pressure), the
current (flow rate) will decrease.

With electricity, this relationship is what is known as linear: double the
voltage and all other factors remaining unchanged, the current will double
as well. Increase it by a factor of 3 and the current will triple. Halve
the resistance and for a constant voltage source, the current will double.
(For you who are hydraulic engineers, this is not quite true with plumbing
as turbulent flow sets in, but this is just an analogy, so bear with me.)

I intend to expose this analogy formally, i.e. electrical and hydraulic circuits are different kinds of models of the same abstract formal theory.

Comments

[old-girl.livejournal.com]

That's a great analogy. I used the waterpipe example to explain basic electronics to my father.

electricity and sound

[peamasii.livejournal.com]

OK, but the analogy pretty much stops there, since you have no hydraulic equivalent for phase, inductivity, charge/capacitance, and other electrical parameters. I think maybe a better one would be to compare sound waves with electrical waves (AC). Then you can talk about effects like sound resonance vs. electrical inductivity, wave propagation vs. resistance, and wave-related measurements like frequency, amplitude, and phase.

[selfishgene.livejournal.com]

Ultimately all arguments are by analogy. You can attempt to refine and improve the analogy but the constraint is always to model the real world in a lump of protoplasm. (Which we call thinking.)

[dkmnow.livejournal.com]

Can an analogy be an analogy for itself?*


(* In AOLspeake, that means "DRH RULZ!")

water transistors

[seattlesque.livejournal.com]

I was actually sketching out a full analogy-based system for electronics as water, in the style of Wally and the Walnuts. My idea was based on the idea of a bunch of people who lived in a desert with no water...but at the center of the desert was a giant cactus that stretched way far up into the sky...so high they couldn't see how high it went.

So the deal was that the people could make holes in the cactus, and the amount of water pressure they would get would be proportional to the size of the hole and the altitude of the hole. The higher you drilled the hole, the more pressure you would get (the cactus narrowed as it went up). But because of the nature of the dirt in the desert, it won't absorb water...so if you poke a hole in the cactus it will flood the whole area.

In order to get around the problem of flooding, they dig out the dirt around the base of the cactus and find that once they dip below ground level, the cactus functions as a vacuum...sucking up the water. How strong a vacuum depended on how deep you made the hole into the base. In any case, they quickly realized that in order to properly harness the water of the cactus without risking a massive flood they needed to ensure that drain capacity was provided to match the hydraulic supply.

In this world, water becomes an unlimited resource...and flooding becomes the real problem. The water pressure is SO strong that the only way to control it once tapped is to route it back into the "ground" from whence it came. So the people tapping the cactus have to route water out AND then back to the base, as with electric current. In this world...if you set up a water connection to your house, the moment you stopped running the water in the faucet you need to switch it over so the feed goes down the drain. (This is different from traditional plumbing, but so it is with magic cacti!)

There are lots of fun design problems where you can teach plumbing principles and build the analogues of capacitors and inductors and resistors...and the idea of a water transistor was going to be a major piece of the work. Centering it all around a "Magic Cactus" in the desert and trying to control flooding helps put a certain urgency and physical reality to the designs that the characters are dealing with...

I've got the drafts for this somewhere. I also have the drafts to an evolving postal service, which starts from being just a physical post where people put notes to a full-on FedEx-style regionally mapped shipping service...with multiple disposable globally unique identifiers for each delivery recipient...