To me, with a interest in railroads, it is clear what one is talking about when an engine in the internal combustion machine and a motor is the electrical machine the turns the axle (and the whole thing is a locomotive).  So I'm with you that there is a difference, and I'd extend it out to engine and motor are two different things even though common usage is sloppier than that.  Maybe as hybrid cars become more common there will be a clearer distinction between the terms as people need to distinguish between the engine and the motors.

From Merriam-Webster online dictionary:

Engine:
4: a machine for converting any of various forms of energy into mechanical force and motion; also : a mechanism or object that serves as an energy source <black holes may be the engines for quasars>

Motor:
1: one that imparts motion; specifically : prime mover
2: any of various power units that develop energy or impart motion: as a: a small compact engine b: internal combustion engine; especially : a gasoline engine c: a rotating machine that transforms electrical energy into mechanical energy

I would never refer to an electrical motor as an engine!

jraef, I agree with your thoughts!
-pmover

While it is common and there are some fairly recent threads that refer to "motoring" an engine, who'd ever think to say in the same context "engining" an engine?  But according to Merriam above that would be proper.  Go figure.

Sorry, but I don't trust civilians with technical definitions.  I used to know the difference in the definitions but I can't remember it right now.

rmw

Thought provoking question.

I think that somewhere way back the word motor comes from the same ancenstry as the word motion.  One example "motor skills".  (skills to produce motion).

Brings to mind a question about the underlying root word in engine and engineer.  Are we called engineers because we are associated with technical things like engines?  Or do engine and engineer both derive from the same word related to our ability to produce an effect.  Beats me.

Clearly in the electrical world we like to reserve the word motor for electric motors. But also there are air motors.  Are they called air motors because they do the same thing as an electric motor, but with air?  Or because they produce motion? The latter, I think (but I'm not sure).  It definitely irritates me when my wife refers to the motor under the car hood.

I agree the terms motoring an engine would be reserved to the context of an engine driving a generator and when the generator is motored the direction of power reverses.  That seems limited to electrical contexts.

Bottom line. Beats me. I would be interested to hear an authoritative rule which covers all applications, but I doubt there is one.

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And would you be more likely to put motor oil in an engine or a motor?

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In aerospace, rockets are considered "motors" as well.

"Art without engineering is dreaming; Engineering without art is calculating."

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Whereas I'd call them (and any jet engine I can think of except plasma drives) internal combustion engines.

Cheers

Greg Locock

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Although they have different root words, they are in effect, the same thing to a degree.  The class of mechanisms we call motors is a subset of what we call engines; engines being the broader category.  We are called Engineers, not Motoreers.  heheehehe

Given that explanation, it does make sense to motor an engine (create motion with the engine), but not engining a motor (convert the motor into motion).  ;)

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

we're not called engineers cos we play with engines, it is because we are ingenious.

Engine is a subset of motor in this context.

Cheers

Greg Locock

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

The same Merriam-Webster online previously cited by pmover tell this about "engine" etymology  :

Etymology: Middle English engineering, from Anglo-French, from Latin "ingenium" natural disposition, talent, from "in"- + "gignere" to beget — more at kin

But for engineer :
Etymology: Middle English engineour, from Anglo-French, from enginer to devise, construct, from engineering

And motor :
Etymology: Latin, from "mov?re" to move

We have commonly only one word in french : "moteur"
L'Office québécoise de la langue française suggest, for the same "engine" definition as from the M-W, both "engine" and "motor". But it proposed "engine" first and would be prefered since they rule it in 2001 and the word "motor" in 1993. They newer definition takes priority. Also, for "moteur" in aerospace it proposed "booster" ("launching rocket" as near synonym) but a rocket is a "fusée".
www.granddictionnaire.com

Talking about confusion?

Danny Garant, ing.jr
Groupe Stavibel Inc.
www.stavibel.qc.ca

I am an engineer because I drive the external combustion locomotive pulling the train.

Well I have to think maybe my x wife was involved in this some how, becouse on my bass boat I have what they call and large outboard motor.

If I attach a 50 horse engine to my boat does it become a engine boat?

No, it becomes an engine water craft.  :)

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

"In aerospace, rockets are considered "motors" as well. "

At the rocket factory where I worked as a young engineer, I was roundly berated for referring to a solid rocket as an engine, or a liquid-propellant engine as a motor.  Frankly, I still claim hogwash, since the elder COB (Crotchety Old Bustard) could not supply a definition that made sense; I agree with the OP's derivation, which implies that rockets are both.

An engine is any useful man-made contrivance that takes in power and possibly raw material, and converts those into a useful output.  This is roughly abstracted from wikipedia's article on engines, and is based on its derivation from the latin, "an invention".  Thus we have Babbage's Difference Engine, or the Middle Ages' Siege Engines, in addition to our modern car engines.

A motor is a sub-class of engines, one that produces motive power as its primary output.  

But, go figure, we are talking about the English language here, and thus have outboard motors on sale next to motorcycle engines, both of which may have electric motors for starting.  Just don't call a solid-fuel rocket an engine, or you will get sneered at.

I hope someone is drawing a Venn diagram of this lot.

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

... or a nice UML description.

- Steve

Then Venn diagram would have to be done with color-shifting spray paint, to give the right fuzzy-edged, shape-shifting dance that the language does.

All cars have engins under hoods. However, carmakers are called General Motors, Ford Motor, etc.

A bike with combustion engin is called motorcycle.

Well it is a motorcar and in England you do drive your car on a motorway.

KENAT, probably the least qualified checker you'll ever meet...

In my understanding...

An engine is an all encompassing term describing some kind of empowering device (usually in the sense of tangible objects but one can then understand how this has been extended to intangible things such as the search engine, graphics engine, economic engine, etc.)

Well now I notice that a motor as an empowering device implies or includes not just motion but 'rotating' motion somewhere within it or connected to it. I can't think of a motor or motor type that does not have this. (Can other contributors here think of one??)

Under this definition (if it is one - it's certainly not a comprehensive one), the term 'engine' might encompass 'motor' as well as other devices. However, the term motor would then not include empowering devices without any rotating mechanisms or parts.

It may be that originally, pretty much all engines were motors but that 'motoreers' didn't sound so elegant.

Sorry blackvision, but we use a lot of Linear Induction Motors, they've been around for some years now and I've never heard them referred to as engines!

It would be interesting to hear what the power units on Maglev trains are called as they use linear induction as motive power.

Trevor Clarke. (R & D) Scientific Instruments.Somerset. UK

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Hmm yes thanks SincoTC, point taken and something that I had overlooked.
This certain is an interesting question (engine vs motor).

Enjoyable it is to see so many answers contributed to this dilemna.

Perhaps eventually it'll all be whittled down to a final result.

Perhaps because the Linear Induction Motor is a kind of induction motor (the stator having been "unrolled" so that it produces a linear force along its length rather than producing a torque), the 'motor' tag has remained.

Thanks blackvision; I'll go along with the "unrolled" inductiom motor, as that's how one of its co-inventors used to demontrate its workings on TV. However, it still leaves us with the (definately non rotary) solid rocket motor.

Over the years, when I've been asked what makes something a motor or an engine, I used the principle that if it was fairly simple and comprised only a few moving parts (or even none), then it was a Motor, i.e. Electric, Rubber (Model Aircraft) and Solid Fuel Rocket. However, if it was complicated and had many components and supporting sub-assemblies, then it was an Engine, i.e. Petrol, Diesel, Jet, Steam and Liquid Fuel Rocket. Unfortunately, it's very easy to blow holes in this method (Ramjet and Airmotor for instance).

Nice as it would be, I doubt that it will ever be resolved to a formula that will satisfy all the years of accepted usage in different disciplines!

Trevor Clarke. (R & D) Scientific Instruments.Somerset. UK

SW2007x64 SP3.0 Pentium P4 3.6Ghz, 4Gb Ram ATI FireGL V7100 Driver: 8.323.0.0
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Thanks again SincoTC.
I've noticed that the air motor also referred to as an air engine and the solid rocket motor is also referred to as a solid rocket engine. The terms seem to be used interchangeably. I've seen the ramjet and its cousin the scramjet referred to as engines, but have not yet seen them referred to as motors. Certainly there's no rotational torque being exploited here.

I do like the principle of the parts count in determining whether a motor or engine, despite the noted exceptions. Certainly within different disciplines established terminologies will be retained and defended. The difficulties of terminology perhaps are heightened as existing disciplines continue to overlap and merge, and as new disciplines are formed.

Probably no singular general rule can be used, but rather a range of answers, the choice influenced by the context of use. Sometimes even context may not be enough and a policy must be established as to terminologies to be used.

electricpete, regarding this"... Are we called engineers because we are associated with technical things like engines?  Or do engine and engineer both derive from the same word related to our ability to produce an effect.  Beats me...:"

I think you should look at the old latin "ingenium", which means "to be good in something", "somebody who uses its brain" or "innovator". I hope I have managed to explain its meaning.

At least this is what I was told at my first day at engineering school (wrongly called engineering university).