Unfortunately sometimes it does.
Early versions of one popular M68K based machine (I forget which)
had a bug that was helped by moving the mouse which generated extra
interruots and sped things up.
Note that everything you have learned about gravity can almost be directly
applied to electricity. In fact the governing equations of EM are almost
exactly the same as that of gravity if you could "remove" the polarity
aspect. (but the consequences can be dramatically different)
Electrons have attraction and repulsion while "matter" has only attraction.
What causet he attraction/repulsion? It is a force. Gravity on one hand and
the electrostatic force on the other.
What about potential energy? Same thing holds for charge. If you take two
charges and bring them close together they will have some sort of potential
energy... they will either attract or repell and that potential will be
converted into kinetic energy just as in mechanics.
Now voltage is a measure of that attraction.
How do you know something has potential energy? You have to let act out on
it. (there is no other way except through analysis but that came about from
Voltage, or the electric potential(vs the mechanical potential) is a really
a difference in potential energy.
So suppose we have +Q C at (-1, 0) and -Q C at (1, 0), they will attract
each other and have forces on them. this would be simiar case to M kg and M
kg but the magnitudes of hte forces would be different.
This attraction gives rise to a potential and the potential difference is
precisely the voltage. (in the right units for charge)
People tend to speak of voltage as if it were a force(such as electromotive
force which has the same units as voltage) but it is not a force just as
mechanical potential isn't a force... but it can be used to create a force.
You hopefully know that the gravitational force can have an associated
potential with it(the mechanical potential). The same is done with the
electric force. Since the forces are conservative we know by mathematics
that there is a scalar field who's gradient is the force. It's much easier
to work with a scalar field and it's called the potential.
In any case thats more theoretical.
What does it mean in practice?
If someone says that they have a capacitor with 10V "across" it what do they
mean? It means they can do some work... and if they were smart they could
compute just how much work. All you need ot know is that if there is a
potential difference between two points, any two points, and you stick a
wire at those two points(a conductor) then current will flow. If you have a
lightbulb or led in series with that wire then it might light up... or you
might be able to turn a wire.
The mere fact that there is a potential difference implies that you can do
work and vice versa. (they are identical concepts as force but viewed from a
It doesn't tell you have much work you can do and infact you might not be
able to do any depending on the circumstances... but at least in theory you
can do some work.
It also is related to current... because current flowing means there is a
potential difference. (but not vice versa)
Analogy: A book on a table. The table is a resistance to the book "flowing"
down to the ground. The book has potential due only to it's position w.r.t
to the earth. If you remove the table the book will convert the
potential(voltage) into kinetic energy(think of current) and when it hits
the ground or something inbetween it would apply a force that can continue
to do work on other things.
There is nothing special about voltage... it's just what we call the
potential for electricity. If you understand the gravitational potential
then you shouldn't have any problem if you just realize that the basic
quanitities one is dealing with are analogous. current = mass flow, voltage
= mechanical potential, force = force, electric field = gravitational field,
What's more important is that you have some concept of magnitude of
voltage... what is 10V? what is 1000V? Also helps to know something about
current and what is 1A vs 100A, etc...
By having that kinda knowledge you'll have a better working understanding.
It's similar to mass and energy. Everyone knows what 100lbs is about... or
maybe even 1000lbs but most people don't know much about energy. Most people
have a better concept of power than energy as they know their lightbulb is
using maybe 100W. They still don't really have any clue what it means but
they do know it is doing something(i.e. work).
And that's all this boils down too... voltage is a measure of work! Work is
what is important! mass is useless if it can't do any work! current is
useless if it can't do any work!! Current is a measure of charge in
motion... which is usefull to determine how much work it can do.
So ultimately in all the things we are trying to do is to simply things to
determine how much work something can do... by knowing that we know how much
less work we have to do. But of course we can't always measure work
directly... we don't have a special machine that we can ask how much work x
is doing and it tells us. We have to break the problem down and learn how to
measure it which involves measuring bits and pieces.
(I don't mean to sound dramatic about it but the fundamentals of physics is
concerned with it)
When did one have to understand electricity to understand how to build a
I'd rather the guy know squat about electricity and be a great bridge
builder than build shitty ass bridges cause he spent to much time trying to
learn about electricity for some school requirements to "broaden his
horizons". He could have spent that time more wisely.
Mechanical engineers don't build bridges either. They do build
automobiles and robots, though. Basic electricity would seem to be
a useful thing for MEs. Basic physics is rather useful, and
required, for EEs. MEs don't have to take the EM semester of
Try a civil engineer if you want a bridge built. I'd rather my
civil engineer had the full load of physics too. We *are* talking
about basic electricity here.
Ok... yes, I know that. Alhtough the overlap is much greater. Learning about
your statics and dynamics is a major part of ME and CE'.
My response was specifically to the statement by Rose.
True... but again, my statement was specifically about roses statement.
He/She is implying that if you don't know even the basics of electricity
then somehow you can't build a good bridge.
What I'm implying is that if the guy is an amazing bridge buildering(Ok, I
know he's ME but Rose is the one who brought up the bridge building) then
it's ok for him to suck as EE.
I'm sure Tesla sucked at ice hockey but I don't see anyone complaining that
he should have spent more time on it. (What does ice hockey have to do with
EE? Who knows but thats not the point)
Also we are getting off the point as if the guy is suppose to be the best.
There are many EE's that don't even have a good understanding of their own
craft so we should get onto those guys first.
Understand. I was debating which one to respond to. ;-)
I don't think you should be an engineer without some knowledge of
basic physics. The fundamental units are rather important in all
engineering disciplines. I'm surely not an ME, but I know F=MA and
you can't push with a rope. ;-)
"Suck as an EE" <> "sucks at fundamental physics"
Understandable. I didn't learn any ice hockey in college physics
The argument wasn't about whether or not there are EEs who shouldn't
be, rather whether it's understandable for an ME to lack basic
electrical knowledge. Would you think it OK for an EE to not know
First off he's still in school... and second he said he didn't understand
voltage... that is only one concept in a huge number of concepts. Also we do
not know to what extent he didn't understand.
I can promise you that many EE graduates do not understand voltage but only
memorized formulas and defnitions..
So it isn't about what's right or wrong but what is real and not real. Sure
I would want everyone to have a little knowledge of everything... but that
isn't practical because then end up not being good at one thing
Did you ever stop to think that maybe the reason he didn't understand it was
that the professor that he took the class from that taught it didn't do a
good job? Do you also realize that there are many levels of understanding
It's not that I don't agree with you that he should understand it and I'm
not even debating that.
But let me ask you something: Suppose he is the best bridge builder in the
world but he doesn't understand voltage... is it "ok"? Can we let it slide
or do we have to send the guy back to kindegarten to learn it? What if it
just can't do it and totally sucks at it? and he doesn't go around
pretending not too but just wants to build bridges... surely it's ok? It's
much better than 99% that don't know and don't give a shit about anything?
I think you guys are jumping to to many conclusions about the guy. We do not
know his circumstances and shouldn't judge him from one post on usenet that
"Hey, I'm in 3rd year mechanical engineering and I still don't feel
like I have a strong understanding of what voltage is. Maybe someone
can help explain the concept."
In fact the question's he asks are quite fair and natural and means he has
an inquisitive mind. So instead of judge him we should try to help him
understand. As long as he doesn't pretend to know something and long as he
doesn't put peoples life at risk then it's not a problem. Sure we can hope
he will understand everything the first time and learn everything he can but
this isn't a fairy tale.
Why? He's a third year engineering student that has zero clue about
a rather important aspect of physics that he *SHOULD* have covered.
It is the equivalent of my not knowing what mechanical force was
when I was a college junior. Somebody failed miserably here.
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