I'm probably wrong about this too, but is seems to me the symmetry might break down if, for example, you just connected the (-) straight to the (+) terminal with no motor in between. It seems to me the (+) plate would be the first thing to heat up as the flow of electrons cascade into it.


PairTheBoard

I'm not entirely sure what you mean by getting rid of the motor. I think you mean doing this:

(+) Jump Battery (-)
| |
| |
| [[Car Frame]]
| |
| |
(+) X DEAD X (-) --

In which case, I think nothing happens because current can't flow across the dead battery.

Not talking about jumping now. Just 1 live battery. Connect the two terminals. I think everything heats up. My thought is that the (+) terminal/battery-plate should heat up first because electrons are cascading into it. So not a symmetric situation.


PairTheBoard

Be certain to call 911 well in advance of doing this experiment. I don't really know what will heat up first but I'm sure you won't have time to measure this either-shorting a car battery is extremely dangerous. Most batteries have > 500 "cold cranking amps" (max current supplied when you start your car, to get it to turn over), this will only flow for a few milliseconds (maybe microseconds) in your scenario before the battery explodes. If you want to test this out try putting your tongue across the terminals of a 9V battery (just for a second), the shock won't kill, won't even hurt you. I'd bet YouTube is a good source of people doing stupid stuff with batteries of all sizes.

LOL

I assume that your intuition here is that you're imagining how water flows off the top of a waterfall smoothly and crashes at the bottom, or something like that.

I don't think this is true, but admittedly I'm not entirely sure. If you short a small battery (something that won't kill you), the entire wire heats up, and not just the terminals. I think this is because the electrons bump into the wire particles as they move through. I don't see why you would not expect the negative terminal to heat up for the same reason. It's not as if the negative terminal is magically collision-free. The actual chemical reaction is happening inside of the battery, and the negative terminal is functionally like a part of a wire.

Motors don't have a plus or minus terminal.

Conventional current flows positive to negative. But it's just a convention. If current is the flow of electrons along a conductor, saying current flows from negative to positive is fine if you're an engineer. Physicists might get their knickers in a twist.

The algebraic sum of voltages dropped across loads in a circuit will equal the source voltage and current is calculated by Ohm's law. We don't have to care which way it flows, we care about the amount of current flowing in a circuit.

If you short a battery with no load, mathematically the current is infinite. Because I=V/R and R = 0. Of course the current isn't really infinite due to the battery's limits/internal resistance but **** gets hot.

Electronics' textbooks are still available in both formats. And it doesn't matter which you buy.

Aha! That's interesting. Is that true for every device that runs on electricity?



PairTheBoard

So maybe it's more like water dropping down a staircase where the energy gets distributed evenly amongst each step?



PairTheBoard

It's true for loads like motors and resistors and inductors. It's not true for semi-conductors, e.g. diodes and transistors. Capacitors come in polarised and non-polarised forms.

If the conductor is a consistent material, yes. Otherwise you have to pull out Ohm's law (voltage varies with resistance) and do some linear algebra.

And MacOneDouble is right about motors not really having a + and - side. Most of them are just a fancy loop of wire and magnets. Depending on the actual construction, there could be a "right way" and "wrong way" to connect them in that you can make the motor turn the opposite direction by switching the polarity.

But not all motors are reversible like this.

Well, the heat is caused by current running through the circuit so basically everything would heat up at the same time. But you're right that everything gets super hot: there's almost no resistance in the circuit so a ****load of current travels through the wire, causing everything to get extremely hot.

Nope. Some devices have diodes, which only let current flow in one direction.

https://en.wikipedia.org/wiki/Diode

A simple motor probably would work fine if you plug it in backwards.

This is a H-Bridge. How you get a DC motor to switch direction.
To explain is simply. The transistors being MOSFETs are voltage controlled switches
and turrned on and off (by a microcontroller typically). If Q3 and Q2 are turned on current flows from Vbat to ground. Turn them off and turn on Q1 and Q4 the motor will switch direction.

The motor produces a back EMF which is why the diodes are there for protection.
https://www.youtube.com/watch?v=LXGtE3X2k7Y



how to delete your pof

edit: lol at the how to delete your pof account. Must be an ad from image host.

For the basics of electricity in a way that is very easy to follow without cutting corners though (like in some very basic books) here is a free book of physics. Go to the relevant chapters to see applications;


https://d3bxy9euw4e147.cloudfront.ne...Physics-OP.pdf

Also basic electronics

http://engineering.nyu.edu/gk12/amps...lectronics.pdf

Also

https://www.circuit-diagram.org/
http://falstad.com/mathphysics.html


How a motor works;

http://hyperphysics.phy-astr.gsu.edu...ic/mothow.html

Batteries

http://hyperphysics.phy-astr.gsu.edu...attery.html#c1

DC water analogy

http://hyperphysics.phy-astr.gsu.edu...watcir.html#c1

Electromagnetism portal and applications

http://hyperphysics.phy-astr.gsu.edu...con.html#emcon

http://hyperphysics.phy-astr.gsu.edu...ehldcn.html#c1

The only circuit in this pdf with values and it's terribly designed.

Well its an introductory free pdf about the basics and how they work. It has a different purpose and its not about circuit design. Plus other circuits exist in the pdf. I am not an engineer so since the thread had no booklet i linked one.

Here is a set of lectures on the basics as well

https://www.youtube.com/playlist?lis...Y9akyObmH2GHP6

and

https://www.youtube.com/watch?v=AfQx...2GHP6&index=27

The component placement is right. But they put in values.
So the amount of base current to saturate the transistor for it to be a reliable switch comes into play, which is based on the collector current - which drives the LED, which is based on the forward voltage drop of the LED: averaging 2V for red, green and yellow and Vce(sat) which is usually 0.2V, but not in this case leaving the remaining question of how much current is driving the LED.
The answer: not enough but it will probably work.

Hyperphysics is awesome.
For electronics I'd recommend allaboutcircuits.