 |
|
|
|
|
|
| |
| |
|
|
|
|
| |
| |
|
|
On 15-6-2009 17:33, Stephen wrote:
> andrel <a_l### [at] hotmail com> wrote:
>> On 15-6-2009 14:02, Stephen wrote:
>>> electrical impulses to the heart are interrupted and fibrillation occurs. IIRC
>>> there are parts of the heart that receive the electrical impulses from the
>>> brain then transmit secondary impulses to the muscle tissue to contract and
>>> relax in an organised way.
>> No the heart is autonomous, will even beat outside the body for some
>> time (hours) if oxygenated. It's frequency can be modulated by stuff in
>> the blood and by nerve tissue that is close to the sinus node when they
>> release special molecules.
>>
>
> I thought that you might respond :)
Thanks for assuming that there are only kids in this newsgroup. ;)
I disagree, a lie for children is when you explain something highly
simplified and/or deliberately wrong because the actual facts are to
difficult. Suggesting that the heart is driven by the nervous system is
simply wrong and what actually happens is just as easy to understand.
Involving the brain will in a bright child immediately lead to questions
what happens when you sleep or are unconscious. The child might even
fear to go to sleep. It does not explain coma or how a paralysed person
can live. So, please, if you have children, tell them a simplification
of the truth, but never that your brain dictates when the heart has to
beat.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
On 15-6-2009 17:56, Invisible wrote:
>>>> No the heart is autonomous, will even beat outside the body for some
>>>> time (hours) if oxygenated.
>>>
>>> Does anybody else find it slightly disturbing that andrel knows such
>>> things?
>>>
>>> I mean, I know there's a good reason, but even so... kinda grusome.
>>
>> As you may be aware, it is my job. It comes with being in a
>> experimental cardiology lab.
>
> Indeed. But still... kinda freaky.
>
>> BTW a beating heart is absolutely not gruesome, I would rather say
>> beautiful. I'd be happy to show you if you happen to be in Amsterdam
>> some time and an experiment is running. ;)
>
> I once saw an operation on TV. They cut open a guy's chest, ripped his
> ripcage apart, and inside was his heart. I swear, it honestly looked
> like it was trying to CLIMB THE HELL OUT OF HIS BODY AND RUN AWAY!! O_O
>
> *shivers*
Was that a dramatazation or an actual procedure?
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
>>> BTW a beating heart is absolutely not gruesome, I would rather say
>>> beautiful. I'd be happy to show you if you happen to be in Amsterdam
>>> some time and an experiment is running. ;)
>>
>> I once saw an operation on TV. They cut open a guy's chest, ripped his
>> ripcage apart, and inside was his heart. I swear, it honestly looked
>> like it was trying to CLIMB THE HELL OUT OF HIS BODY AND RUN AWAY!! O_O
>>
>> *shivers*
>
> Was that a dramatazation or an actual procedure?
It was meant to be the real thing. Apparently there was something or
other wrong with this guy's heart, so they were going to rip it out and
stick a new one in. (I wasn't really paying attention.) The new heart
looked rather limp and pale. But the still-beating one looked evil! (And
several sizes too big for the chest cavity, BTW...)
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
On 15-6-2009 19:26, Orchid XP v8 wrote:
>>>> BTW a beating heart is absolutely not gruesome, I would rather say
>>>> beautiful. I'd be happy to show you if you happen to be in Amsterdam
>>>> some time and an experiment is running. ;)
>>>
>>> I once saw an operation on TV. They cut open a guy's chest, ripped
>>> his ripcage apart, and inside was his heart. I swear, it honestly
>>> looked like it was trying to CLIMB THE HELL OUT OF HIS BODY AND RUN
>>> AWAY!! O_O
>>>
>>> *shivers*
>>
>> Was that a dramatazation or an actual procedure?
>
> It was meant to be the real thing. Apparently there was something or
> other wrong with this guy's heart, so they were going to rip it out and
> stick a new one in. (I wasn't really paying attention.) The new heart
> looked rather limp and pale. But the still-beating one looked evil! (And
> several sizes too big for the chest cavity, BTW...)
I think I would not use 'rip' and 'stick' to describe the procedure.
That the heart to be explanted is big and ugly is to be expected. The
ones I see are all failing hearts and these are huge, and if the patient
is older they are yellow with fat. Yes, I do sometimes see them. Guess
what we are doing with them...
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
>> A pretty accurate model of a battery is a perfect voltage source in
>> series with an "internal" resistor. This then nicely explains how the
>> more current you try to draw the lower the apparent voltage will be at
>> the terminals of the battery.
>
> As far as I'm aware, resistors affect only current, not potential.
That statement doesn't even make sense. The voltage across the terminals of
a resistor is equal to the current going through it times the resistance,
that's all you need to know and then you can figure out any resistor circuit
with a bit of algebra.
By the way, notice how the lights dim on your car (and maybe your radio also
shuts off?) when you start the engine? That's because the starter motor is
drawing a huge current and causing the battery voltage to drop to way below
12V.
Your lights are connected directly to the battery supply, so they dim, and
the radio might only be specced to work down to 8V or something, in which
case it shuts itself off until the voltage comes back up again. Some radios
can survive very low voltages for short periods of time, so they usually
stay on while the engine is being started, but not on all cars.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
>> As far as I'm aware, resistors affect only current, not potential.
>
> That statement doesn't even make sense.
As the resistence of a circuit increases, the current flowing through it
decreases. But that doesn't affect the actual potential across the circuit.
Or rather, that's what the books I've read claim, anyway...
> By the way, notice how the lights dim on your car (and maybe your radio
> also shuts off?) when you start the engine?
Yeah. That's because there's a limit to how much current the battery can
supply.
Indeed, I'm told the only reason cars use lead acid batteries (which are
very heavy yet don't actually hold that much charge) is so that they can
briefly deliver the astronomical current required to turn the starter
motor. From the sources I've read, if it weren't for that, you'd only
need a battery a fraction of the size to run the spark plugs, headlights
and other electrical bits.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Invisible wrote:
>
> As the resistence of a circuit increases, the current flowing through it
> decreases. But that doesn't affect the actual potential across the circuit.
That's as long as the resistance on the feeding wires is small enough to
be uncompareable to the resistance of the actual device. Actually, even
then the change of the potential is just so small that you can't measure it.
> Or rather, that's what the books I've read claim, anyway...
I bet they are "for teh n00bz" -level books :).
> Yeah. That's because there's a limit to how much current the battery can
> supply.
And that's because of the internal resistance. If there were no such
thing, what would limit the current?
> Indeed, I'm told the only reason cars use lead acid batteries (which are
> very heavy yet don't actually hold that much charge) is so that they can
> briefly deliver the astronomical current required to turn the starter
> motor.
Actually cars use lead acid batteries because they still are just the
best way to deliver that current reliably. NiCD -batteries can't stand
uneven charging, NiMH -batteries can't deliver enough current IIRC,
Litium batteries (both LiPo and Li-ion) can't stand water-freezing
temperatures. It all actually makes sense :).
> From the sources I've read, if it weren't for that, you'd only
> need a battery a fraction of the size to run the spark plugs, headlights
> and other electrical bits.
Actually you wouldn't need a battery to run those things, you'd just
need a battery/capacitor to regulate the current coming from the alternator.
-Aero
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
>> Or rather, that's what the books I've read claim, anyway...
>
> I bet they are "for teh n00bz" -level books :).
Well, it does say "ages 5 and above"...
>> Yeah. That's because there's a limit to how much current the battery can
>> supply.
>
> And that's because of the internal resistance. If there were no such
> thing, what would limit the current?
I'm sure there's a logic there somewhere - it just doesn't make any
sense to *me*. ;-)
>> Indeed, I'm told the only reason cars use lead acid batteries (which are
>> very heavy yet don't actually hold that much charge) is so that they can
>> briefly deliver the astronomical current required to turn the starter
>> motor.
>
> Actually cars use lead acid batteries because they still are just the
> best way to deliver that current reliably. NiCD -batteries can't stand
> uneven charging, NiMH -batteries can't deliver enough current IIRC,
> Litium batteries (both LiPo and Li-ion) can't stand water-freezing
> temperatures. It all actually makes sense :).
...as I said, you need the wattage to turn the starter motor. ;-) If you
only needed electricity for the sparks and lights and stuff, you
wouldn't need nearly as much power. (Freezing would still be an issue
tho...)
>> From the sources I've read, if it weren't for that, you'd only
>> need a battery a fraction of the size to run the spark plugs, headlights
>> and other electrical bits.
>
> Actually you wouldn't need a battery to run those things, you'd just
> need a battery/capacitor to regulate the current coming from the alternator.
Not if you expect the headlights to work while the engine isn't running. ;-)
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
andrel <a_l### [at] hotmailcom> wrote:
> Thanks for assuming that there are only kids in this newsgroup. ;)
>
Only?
> I disagree, a lie for children is when you explain something highly
> simplified and/or deliberately wrong because the actual facts are to
> difficult. Suggesting that the heart is driven by the nervous system is
> simply wrong and what actually happens is just as easy to understand.
> Involving the brain will in a bright child immediately lead to questions
> what happens when you sleep or are unconscious. The child might even
> fear to go to sleep. It does not explain coma or how a paralysed person
> can live. So, please, if you have children, tell them a simplification
> of the truth, but never that your brain dictates when the heart has to
> beat.
Stephen
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Invisible wrote:
>
> Well, it does say "ages 5 and above"...
As assumed :).
>>> Yeah. That's because there's a limit to how much current the battery can
>>> supply.
>>
>> And that's because of the internal resistance. If there were no such
>> thing, what would limit the current?
>
> I'm sure there's a logic there somewhere - it just doesn't make any
> sense to *me*. ;-)
That logic IS the internal resistance. You'd just need to put some mind
to it (and maybe read a book for ages 15 and above), and you'd certainly
figure it out.
>> Actually cars use lead acid batteries because they still are just the
>> best way to deliver that current reliably. NiCD -batteries can't stand
>> uneven charging, NiMH -batteries can't deliver enough current IIRC,
>> Litium batteries (both LiPo and Li-ion) can't stand water-freezing
>> temperatures. It all actually makes sense :).
>
> ...as I said, you need the wattage to turn the starter motor. ;-)
Yes. You can have the wattage from numerous different battery types. The
problem is that you can't have the wattage from any other battery type
reliably enough, or in a package that actually fits in the car.
> If you
> only needed electricity for the sparks and lights and stuff, you
> wouldn't need nearly as much power. (Freezing would still be an issue
> tho...)
Yep, indeed it would. Lead acid handles freezing temperatures incredibly
well and in small package.
BTW, when there's *really* cold outside, the battery won't give as much
current out, thus not starting the car. To beat this you can use the
internal resistance to heat up the battery a bit (eg. by putting your
park lights on) and then start the car. Viva la resistance!
> Not if you expect the headlights to work while the engine isn't running.
> ;-)
True. The headlights are traditionalle 55W halogens and tail light
(which are lit when headlights are lit) 5W halogens (and there's usually
4 of them). Parks are also usually 5W halogens, that makes
55*2+5*6=140W, which makes ~12A of current, which makes under 6 hours to
drain the normal ~60Ah battery empty or less to drain it to the point
the current won't be enough for starting the engine. Therefore it's a
good idea not to use the headlights too much while the engine ain't
running ;-).
-Aero
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
|
|
