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Am 17.05.2010 21:46, schrieb Warp:
>> The farmer doesn't want to kill the cow. He wants to tingle the cow enough
>> that the cow learns not to lean against the fence.
>
> Hence 1.5 volts isn't going to do it.
Well, with a proper circuit you /can/ power the whole thing with a 1.5 V
battery, if only for limited time.
Heck, with a 1.5 V battery and suitable circuitry you can generate a
pulse powerful enough to kill at least small animals like flies (ever
heard of electric flyswatters?); I'm not sure whether a cattle fence is
strong enough to accomplish even that.
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And lo On Tue, 18 May 2010 12:34:53 +0100, Warp <war### [at] tag povrayorg> did
spake thusly:
> Phil Cook v2 <phi### [at] nospamrocainfreeservecouk> wrote:
>> Just to act on the dumb side. If you use a graduated beaker with a
>> candle
>> in it, add the water, and the second beaker, and then measure the water
>> height. Shouldn't the increase in temperature in the up-turned beaker
>> create a high-pressure that forces the water out from under it and thus
>> an
>> increase in the water height as measured in the graduated beaker? So why
>> is the level of water forced out by the high-pressure less than the
>> amount
>> 'sucked' in by the low-pressure?
>
> I didn't understand the question.
The water is 'sucked' in because the cooling air inside the beaker lowers
the pressure, but prior to that the air was hot and therefore should be at
a higher pressure and force the water out of the beaker. Why does water
out not equal water in?
As an additional thought set up the experiment three times identically
except in Exp1 use a room-temperature beaker, in Exp2 a beaker straight
from a warming-oven, in Exp3 a beaker from a refrigerator. Would you
expect to see any difference in the water level when the flame goes out?
--
Phil Cook
--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com
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clipka <ano### [at] anonymousorg> wrote:
> Am 17.05.2010 21:46, schrieb Warp:
> >> The farmer doesn't want to kill the cow. He wants to tingle the cow enough
> >> that the cow learns not to lean against the fence.
> >
> > Hence 1.5 volts isn't going to do it.
> Well, with a proper circuit you /can/ power the whole thing with a 1.5 V
> battery, if only for limited time.
The point was that something like 1.5 volts between the wire and the
ground isn't going to do anything. You need something like 40 kilovolts
between them. Only then will you get that huge shock when you touch it.
(How you get it charged and with what, is an irrelevant question.)
--
- Warp
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clipka <ano### [at] anonymousorg> wrote:
> Aside from that, I have no idea what the comparison with an 1.5V battery
> has to do with the sentence of mine you quoted.
The quote was a kind of summary of the whole discussion. I don't like
quoting 40 lines and then writing a 2-line answer to it.
--
- Warp
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Phil Cook v2 <phi### [at] nospamrocainfreeservecouk> wrote:
> The water is 'sucked' in because the cooling air inside the beaker lowers
> the pressure, but prior to that the air was hot and therefore should be at
> a higher pressure and force the water out of the beaker. Why does water
> out not equal water in?
The glass is put on the plate *after* the candle has been lit, so the air
around the candle is already hot.
An interesting experiment would be to put the glass first and *then* light
the candle to see what happens. (Of course you have to devise a way to do
that. A magnifying glass and sunrays might be enough.)
--
- Warp
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Am 19.05.2010 13:49, schrieb Warp:
> clipka<ano### [at] anonymousorg> wrote:
>> Aside from that, I have no idea what the comparison with an 1.5V battery
>> has to do with the sentence of mine you quoted.
>
> The quote was a kind of summary of the whole discussion. I don't like
> quoting 40 lines and then writing a 2-line answer to it.
Quoting 2 sentences instead of 1 would have sufficed to quote my whole
posting minus what I quoted there.
Then again, maybe you perfectly misread that sentence you quoted:
"Note that the probability that you're making contact with the cattle
wire at the very moment that a pulse has just started is /very/ low."
Did you perhaps misread that as "The voltage is /very/ low"?
Read the sentence again then, as that's /not/ what I wrote. There's no
mentioning of the voltage in that sentence. I was writing about a
/probability/ there which I claimed to be very low.
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clipka <ano### [at] anonymousorg> wrote:
> Then again, maybe you perfectly misread that sentence you quoted:
> "Note that the probability that you're making contact with the cattle
> wire at the very moment that a pulse has just started is /very/ low."
> Did you perhaps misread that as "The voltage is /very/ low"?
> Read the sentence again then, as that's /not/ what I wrote. There's no
> mentioning of the voltage in that sentence. I was writing about a
> /probability/ there which I claimed to be very low.
The probability of what? The voltage being extremely high? Hence you
make it sound like most of the time the voltage is far from its peak,
and thus touching the fence is no different than touching eg. a battery.
--
- Warp
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4bf3d0f0@news.povray.org...
> Phil Cook v2 <phi### [at] nospamrocainfreeservecouk> wrote:
>> The water is 'sucked' in because the cooling air inside the beaker lowers
>> the pressure, but prior to that the air was hot and therefore should be
>> at
>> a higher pressure and force the water out of the beaker. Why does water
>> out not equal water in?
>
> The glass is put on the plate *after* the candle has been lit, so the air
> around the candle is already hot.
Even if not already hot, as air volume inflates, water level in the beaker
reaches the edge of the glass and gets bubbling out.
Now there is less air in the beaker than before the beginning of the
experiment !
As the surface of the plate is bigger than that of the beaker, when air gets
colder and volume smaller, water can rise faster in the beaker than it
lowers in the plate.
At equal temperature, volume is smaller than before because there is less
air :)
Marc
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Am 19.05.2010 15:18, schrieb Warp:
>> Read the sentence again then, as that's /not/ what I wrote. There's no
>> mentioning of the voltage in that sentence. I was writing about a
>> /probability/ there which I claimed to be very low.
>
> The probability of what? The voltage being extremely high? Hence you
> make it sound like most of the time the voltage is far from its peak,
> and thus touching the fence is no different than touching eg. a battery.
No, the probability that you /start making/ contact with the wire /the
very instant/ the pulse goes off (vs. the probability of you /already
being/ in contact at that moment).
My primary point there being that the picture you draw about the
operation of a cattle fence applies only to very rare cases, and is
therefore pretty moot regarding assessment of why it is generally both
painful but harmless (even though of course the odd scenario needs to be
taken into account to make sure it is /always/ harmless).
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On 5/19/2010 8:29 AM, M_a_r_c wrote:
> As the surface of the plate is bigger than that of the beaker, when air gets
> colder and volume smaller, water can rise faster in the beaker than it
> lowers in the plate.
Actally, the real reason is one of the combustion products, water,
condenses as it reaches room temperature, reducing the amount of gas
in the glass, thus allowing the water from the dish to be pulled in, due
to the pressure drop.
--
~Mike
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