Water/electricity analogy

[italia458]

One of my students today told me that the water/electricity analogy isn't really correct/accurate in explaining the basics of electricity. I had compared voltage to water pressure, current to water flow and capacity to the amount of water in a container. I understand analogies obviously don't explain things fully but is there something wrong with using this analogy?

Here is a link explaining the analogy: Water circuit analogy to electric circuit (http://hyperphysics.phy-astr.gsu.edu/hbase/electric/watcir.html)

[MarkerInbound]

Did the student say what was wrong with the analogy?

[Taras B]

The water analogy is a fine teaching tool, but it is only accurate to a point: Once you get into more complicated principles such as induction coils, the analogy doesn't work anymore, due to the lack of electromagnetic properties of water, ie, flowing water does not create an electric field:

http://www.hattorikogyo.com/ihe/what/ih_diagram.gif

:8

[blackhand]

The analogy has been used for as long as I remember, and is accurate enough for basics.
Ask the student why he finds the analogy is wrong.

[chris weston]

I've used this analogy for decades without difficulty, students normally find that it helps when doing basic cell theory, Nernst, E cell v E Standard etc.

But, as explained above and like many analogies, it has its limitations.

Physicists get uneasy when using it as students then start to follow electron flow in circuits rather than conventional current. Chemists just smile!

CW

[Mike744]

The water analogy provides a basic understanding but as previously mentioned has its limitations. The progression to Kirchhoff's laws also has its limitations - nothings perfect :E

[barit1]

Having instructed technical subjects for many years, I always admonish students that I will use analogies for introductory lessons, but will attempt to draw the line when the analogy starts to break down.

Example: Helo turbine engines have a governor to hold a constant rotor speed through climb, cruise, descent, & hover; fairly similar to cruise control of your auto. If you climb too steep a hill in your car, it "runs out of steam" and the car slows down. Likewise if you pull too much collective in your whirly. The details of why this speed falloff are DIFFERENT in the two cases.

[lomapaseo]

barit1

Example: Helo turbine engines have a governor to hold a constant rotor speed through climb, cruise, descent, & hover; fairly similar to cruise control of your auto. If you climb too steep a hill in your car, it "runs out of steam" and the car slows down. Likewise if you pull too much collective in your whirly. The details of why this speed falloff are DIFFERENT in the two cases

The crux of the Colgan copter accident

One side claims fuel starvation, while the other side claims load dip

[cwatters]

The water/electricity analogy works quite well but for some electronic devices the water equivalent is too complicated to be useful. This page has a list of water equivalents for things such as inductors and even transistors...

Hydraulic analogy - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Hydraulic_analogy)

Perhaps your student is just trying to show off. Perhaps ask him if he knows a better one?

[italia458]

Perhaps your student is just trying to show off. Perhaps ask him if he knows a better one?

I think that's the case.

[FCeng84]

As a second year undergraduate student at MIT in the early 80's we had an intro level course in the mechanical engineering department that took this analogy a step further. We were introduced to the parallels between electrical, hydraulic, and mechanical systems. The concepts of "across variables" (voltage, presssure, and force) and "through variables" (current, fluid flow, and velocity) were at the core of this course. I remember this class as an eye openner that has stuck with me ever since. I just looked at the current MIT Mech Eng course list and things have changed a bit, but there are a pair of Dynamics and Control courses that look to cover this and more material from a similar starting point. Worked (and still works) for me.

[NWSRG]

As an electrical engineering undergraduate, with perhaps more natural inclination towards mechanical engineering, I always liked to consider inductors and capacitors as springs and shock absorbers! Made much more sense...

[Fursty Ferret]

FCeng84 / NWSRG:

Exactly how I was taught the introduction to undergraduate physics.

[EEngr]

.... the beer/foam analogy.

Sometimes it takes several tries to cover the finer points of power factor.:ok: