1119: "Undoing"

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1119: "Undoing"

Postby Quicksilver » Wed Oct 10, 2012 4:01 am UTC

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Alt Text:"I've been sneaking out at night and installing lamps on the underside of every photovoltaic panel I can find. Sure, there are upwards of 80% losses, but I prefer to think of them as nearly 20% gains."
Another hobby comic. I wonder where you find wind farms where this would be easy to do.

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Re: 1119: "Undoing"

Postby rhomboidal » Wed Oct 10, 2012 4:05 am UTC

You know you have a pretty interesting hobby if it could give Al Gore an aneurysm.

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Re: 1119: "Undoing"

Postby Djehutynakht » Wed Oct 10, 2012 4:06 am UTC

I wonder where he finds the materials to build additional windmills.


Although I suppose all they have to do is switch around the directions of the new windmills and they can double their output.

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Re: 1119: "Undoing"

Postby Schrollini » Wed Oct 10, 2012 4:21 am UTC

Alt Text:"I've been sneaking out at night and installing lamps on the underside of every photovoltaic panel I can find. Sure, there are upwards of 80% losses, but I prefer to think of them as nearly 20% gains."

My father, a traffic engineer, tells of a time they were installing a new sign with some electrical part. (Flashing lights perhaps?) In the interest of environmental friendliness, they decided to put a photovoltaic panel on top of the sign, instead of hooking it up to the grid. After it was installed, he went to see it....

And discovered it had been placed directly below a streetlight.

The good news was that the battery was always fully charged.
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Re: 1119: "Undoing"

Postby sardia » Wed Oct 10, 2012 4:40 am UTC

Schrollini wrote:
Alt Text:"I've been sneaking out at night and installing lamps on the underside of every photovoltaic panel I can find. Sure, there are upwards of 80% losses, but I prefer to think of them as nearly 20% gains."

My father, a traffic engineer, tells of a time they were installing a new sign with some electrical part. (Flashing lights perhaps?) In the interest of environmental friendliness, they decided to put a photovoltaic panel on top of the sign, instead of hooking it up to the grid. After it was installed, he went to see it....

And discovered it had been placed directly below a streetlight.

The good news was that the battery was always fully charged.

Well that's not too bad, the lamp is off during the day, when the panel is generating the most power. As for night time, those lamps were gonna be on anyway.

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Re: 1119: "Undoing"

Postby Primis » Wed Oct 10, 2012 4:59 am UTC

I thought about that for a watermill once, but the conservation of energy make my head hurt
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Re: 1119: "Undoing"

Postby Catprog » Wed Oct 10, 2012 5:08 am UTC

Schrollini wrote:
Alt Text:"I've been sneaking out at night and installing lamps on the underside of every photovoltaic panel I can find. Sure, there are upwards of 80% losses, but I prefer to think of them as nearly 20% gains."

My father, a traffic engineer, tells of a time they were installing a new sign with some electrical part. (Flashing lights perhaps?) In the interest of environmental friendliness, they decided to put a photovoltaic panel on top of the sign, instead of hooking it up to the grid. After it was installed, he went to see it....

And discovered it had been placed directly below a streetlight.

The good news was that the battery was always fully charged.


For small power usage the grid connection fee can cost more then the solar panels.

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Re: 1119: "Undoing"

Postby Eutychus » Wed Oct 10, 2012 5:10 am UTC

Shouldn't this be a "What-if"?

I've always wondered about the effect of wind turbines on the wind. This comic suggests there is less wind, um, downwind of the turbine. Sure, not as much less as is suggested here, but doesn't a huge wind farm have a measurable effect? Wouldn't the same thing apply to tidal/wave power?

/not a scientist
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Re: 1119: "Undoing"

Postby rapturemachine » Wed Oct 10, 2012 5:13 am UTC

I think it would be better if they were facing each other. Assuming that the amount of wind from the fan is enough for the wind turbine to generate enough power to keep powering the fan... :)

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Re: 1119: "Undoing"

Postby Catprog » Wed Oct 10, 2012 5:17 am UTC

Eutychus wrote:Shouldn't this be a "What-if"?

I've always wondered about the effect of wind turbines on the wind. This comic suggests there is less wind, um, downwind of the turbine. Sure, not as much less as is suggested here, but doesn't a huge wind farm have a measurable effect? Wouldn't the same thing apply to tidal/wave power?

/not a scientist


Yes, but their is quite a bit more wind compared to human power usage.

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Re: 1119: "Undoing"

Postby Pfhorrest » Wed Oct 10, 2012 5:26 am UTC

Eutychus wrote:Shouldn't this be a "What-if"?

I've always wondered about the effect of wind turbines on the wind. This comic suggests there is less wind, um, downwind of the turbine. Sure, not as much less as is suggested here, but doesn't a huge wind farm have a measurable effect? Wouldn't the same thing apply to tidal/wave power?

/not a scientist

Necessarily, yes. Virtually every kind of electric power generation depends on converting the kinetic energy of some moving medium into electrical energy. Hydroelectric turbines also slow the outflow of water from dams, etc. Even gas, coal, and nuclear power work by heating a medium, like air or water or the combustion's own exhaust, which then flows out into a cooler surrounding medium, and that motion is then converted into electricity (slowing and cooling the working medium in the process). And conversely, since heat is just aggregate motion, things like wave and wind power have a large-scale effect of extracting heat from the atmosphere and oceans, as that is where the motion comes from to begin with, and where it goes back to after the motion dissipates.

That heat in turn comes from the sun, so all of these energy sources are effectively solar power by proxy. Hydroelectric as well, as the sun heats the water which rises and then falls as rain to fill the lakes that power the turbines as they flow back to the sea. All kinds of carbon power as well, as the energy in the organisms that become coal, oil, etc, ultimately derives from plants' photosynthesis, converting solar energy into chemical energy.

The sun of course is fusion-powered, and fusion is the source of the fissionable materials that power nuclear power plants. So really, every power source is some indirect form of fusion.

I'd make an argument that as stars are fused by gravity, everything is really gravity-powered, but I'll leave that for another day.
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Re: 1119: "Undoing"

Postby icefest » Wed Oct 10, 2012 5:41 am UTC

I've always wondered about the effect of wind turbines on the wind. This comic suggests there is less wind, um, downwind of the turbine


There once was a German scientist who asked a very similar question. He then went to prove the maximum energy a windmill can extract from wind (59.3%)
If you want to know the following wind speed, remember that wind energy increases with the cube of the wind speed.

Read about it here: http://en.wikipedia.org/wiki/Betz%27_law

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Re: 1119: "Undoing"

Postby CarlLaMagouille » Wed Oct 10, 2012 5:44 am UTC

Pfhorrest wrote:So really, every power source is some indirect form of fusion.


Except maybe for Tidal power, which can be achieved without the sun, only with the moon.

This of course, brings you to your later conclusion that everything is gravity-powered...

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Re: 1119: "Undoing"

Postby CorruptUser » Wed Oct 10, 2012 5:53 am UTC

Wait a sec, wouldn't harvesting tidal forces eventually slow the moon down, bringing the moon 'closer' to the Earth, and a trillion years after the sun has scraped the mantle off of the Earth, cause the moon to crash, dooming us all?

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Re: 1119: "Undoing"

Postby mcdigman » Wed Oct 10, 2012 5:58 am UTC

CarlLaMagouille wrote:Except maybe for Tidal power, which can be achieved without the sun, only with the moon.


Well, the surface of the earth has to be warm for the oceans to be liquid, which is +1 for the sun and fusion/fission in general.
Unless you are on Enceladus, where the tidal forces alone heat the water enough to keep it liquid...

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Re: 1119: "Undoing"

Postby Seeker160 » Wed Oct 10, 2012 6:15 am UTC

Eutychus wrote:Shouldn't this be a "What-if"?

I've always wondered about the effect of wind turbines on the wind. This comic suggests there is less wind, um, downwind of the turbine. Sure, not as much less as is suggested here, but doesn't a huge wind farm have a measurable effect? Wouldn't the same thing apply to tidal/wave power?

/not a scientist

EDIT: OK so on look two it appears my intuition was backwards and I have trouble interpreting directionality of squiggly lines but I am leaving my explanation because I love the Ultimate Machine

So I think the point here is that the fan is blowing air the opposite direction that the wind is blowing. So if the the turbine is spinning in lets say arbitrary wind speed and direction of 10 mph wind going north then it providing enough power to make the fan spin at let's say 4.8 mph south (randomly choosing 60% turbine efficiency and 80% motor efficiency). But the problem is that isn't true now because now your wind speed is (+10 - 4.8) = so 5.2mph north but now your fan speed is slower then 4.8 mph south so it keeps adjusting itself. I would assume it would find an equilibrium eventually but basically the equilibrium would only be because of the overall 48% efficiency of my example system.

NOTE: all numbers were randomly chosen to help my explanation.
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Re: 1119: "Undoing"

Postby phlip » Wed Oct 10, 2012 6:27 am UTC

CorruptUser wrote:Wait a sec, wouldn't harvesting tidal forces eventually slow the moon down, bringing the moon 'closer' to the Earth, and a trillion years after the sun has scraped the mantle off of the Earth, cause the moon to crash, dooming us all?

Actually, the other way around - the moon's orbit gets more distant over time due to tidal effects. It also slows the earth's rotation slightly. This will continue until the period of the moon's orbit is equal to the length of a day, and thus the moon will always be over the same point on Earth (in much the same way as roughly the same point on the moon always points towards the Earth now), at which point the tides will be static, and there'll be no way to extract any energy from them. Note that this is happening anyway, due to the inconvenient fact that the oceans have nonzero viscosity... harvesting tidal forces just makes it happen infinitesimally quicker.

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Re: 1119: "Undoing"

Postby CorruptUser » Wed Oct 10, 2012 6:33 am UTC

But tidal harnesses slow the flow of ocean water, reducing viscosity, so wouldn't that mean it delays the process? Sorry if I'm asking stupid questions here.

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Re: 1119: "Undoing"

Postby phlip » Wed Oct 10, 2012 6:51 am UTC

Viscosity is just resistance to flowing - it slows down the flowing of the tide, so it's slightly behind where the moon is, which in turn is what causes the tidal locking effects. Anything that slows down the flowing of the tide will add to that effect.

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Re: 1119: "Undoing"

Postby ijuin » Wed Oct 10, 2012 7:02 am UTC

Eutychus wrote:Shouldn't this be a "What-if"?

I've always wondered about the effect of wind turbines on the wind. This comic suggests there is less wind, um, downwind of the turbine. Sure, not as much less as is suggested here, but doesn't a huge wind farm have a measurable effect? Wouldn't the same thing apply to tidal/wave power?

/not a scientist

I can't for the life of me remember the web address, but I recall reading something a while back claiming that if we blanketed the entire continent with turbines at the maximum density possible (all at ground level), it would absorb just shy of thirty percent of the total wind energy at ground level.

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Re: 1119: "Undoing"

Postby Linux0s » Wed Oct 10, 2012 8:59 am UTC

I guess that's one way to shoot the breeze.
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Re: 1119: "Undoing"

Postby da Doctah » Wed Oct 10, 2012 10:56 am UTC

I'm somehow reminded of the time David Letterman put a humidifier and a dehumidifier in the studio during his show and let them fight it out for an hour. (If memory serves, the dehumidifier was gaining on its counterpart by a small margin.)

Or Steven Wright's idea for a battery-powered battery charger.

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Re: 1119: "Undoing"

Postby rmsgrey » Wed Oct 10, 2012 11:21 am UTC

da Doctah wrote:Or Steven Wright's idea for a battery-powered battery charger.


Ultimately, all our forms of "energy generation" are are ways of converting one form of stored energy into another - sometimes very volatile storage, but still ways of keeping the energy until it's used or dissipated.

In that light, the only thing that's silly about a battery-powered battery charger is that it would be "converting" energy from one form to a very similar one - with more general "batteries", that may be sensible - for example, using the flow of water from a water-tower (gravitational potential battery) to drive a turbine to power something, and tapping that power to charge your iPod at the same time...

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Re: 1119: "Undoing"

Postby twcarlson » Wed Oct 10, 2012 12:10 pm UTC

Seeker160 wrote:
Eutychus wrote:Shouldn't this be a "What-if"?

I've always wondered about the effect of wind turbines on the wind. This comic suggests there is less wind, um, downwind of the turbine. Sure, not as much less as is suggested here, but doesn't a huge wind farm have a measurable effect? Wouldn't the same thing apply to tidal/wave power?

/not a scientist

EDIT: OK so on look two it appears my intuition was backwards and I have trouble interpreting directionality of squiggly lines but I am leaving my explanation because I love the Ultimate Machine

So I think the point here is that the fan is blowing air the opposite direction that the wind is blowing. So if the the turbine is spinning in lets say arbitrary wind speed and direction of 10 mph wind going north then it providing enough power to make the fan spin at let's say 4.8 mph south (randomly choosing 60% turbine efficiency and 80% motor efficiency). But the problem is that isn't true now because now your wind speed is (+10 - 4.8) = so 5.2mph north but now your fan speed is slower then 4.8 mph south so it keeps adjusting itself. I would assume it would find an equilibrium eventually but basically the equilibrium would only be because of the overall 48% efficiency of my example system.

NOTE: all numbers were randomly chosen to help my explanation.
Basically it's the ultimate machine
http://www.youtube.com/watch?feature=pl ... MGJB410Ccs

The right fan is not pushing against the left turbine's air — the wind blows left to right the whole time.

The left turbine is harvesting wind that is moving from left to right, slowing the wind speed and outputting electrical energy. Then the jerk stick figure taps the electricity and runs a fan (also blowing from left to right), effectively undoing the whole setup (assuming perfect efficiency).

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Re: 1119: "Undoing"

Postby dp2 » Wed Oct 10, 2012 12:35 pm UTC

ijuin wrote:
Eutychus wrote:Shouldn't this be a "What-if"?

I've always wondered about the effect of wind turbines on the wind. This comic suggests there is less wind, um, downwind of the turbine. Sure, not as much less as is suggested here, but doesn't a huge wind farm have a measurable effect? Wouldn't the same thing apply to tidal/wave power?

/not a scientist

I can't for the life of me remember the web address, but I recall reading something a while back claiming that if we blanketed the entire continent with turbines at the maximum density possible (all at ground level), it would absorb just shy of thirty percent of the total wind energy at ground level.

I've wondered the same thing about solar panels. We talk about having large fields of them in the desert. But that is removing a lot of energy that is keeping that area desert. Google "saharan dust" and you'll get an idea of how even a small piece of desert may be important on a global scale. Making a desert more (literally) green is not necessarily a good thing for the global climate.

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Re: 1119: "Undoing"

Postby cellocgw » Wed Oct 10, 2012 1:04 pm UTC

da Doctah wrote:I'm somehow reminded of the time David Letterman put a humidifier and a dehumidifier in the studio during his show and let them fight it out for an hour. (If memory serves, the dehumidifier was gaining on its counterpart by a small margin.)

Or Steven Wright's idea for a battery-powered battery charger.


I own a battery-powered battery charger (you insensitive clod). Well, technically, it's a portable backup battery, but it does simultaneously drive and recharge my phone or tablet.

And, yes, you pedants, it cannot recharge itself.
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Re: 1119: "Undoing"

Postby JustEric » Wed Oct 10, 2012 1:41 pm UTC

da Doctah wrote:Or Steven Wright's idea for a battery-powered battery charger.

Image

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Re: 1119: "Undoing"

Postby endolith » Wed Oct 10, 2012 2:00 pm UTC

Eutychus wrote:I've always wondered about the effect of wind turbines on the wind. This comic suggests there is less wind, um, downwind of the turbine.


If the air is moving faster upstream from the turbine, and slower downstream, then there's a constantly increasing accumulation of air at the turbine, which would eventually liquefy under the pressure. :)

I would guess that it works the same way for air as it does for electrical current, and the wind speed slows both in front of and behind the turbine, due to the obstruction and air pushing on air.


Wouldn't the same thing apply to tidal/wave power?


I heard wave power creates a zone free of waves in its wake, which disrupts the environment, because all the organisms that live on the beach are evolved specifically to live in waves, which uncover food particles, etc.

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Re: 1119: "Undoing"

Postby Envelope Generator » Wed Oct 10, 2012 2:26 pm UTC

This will be R. Munroe's cover story when XKCD goes offline.
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Re: 1119: "Undoing"

Postby super dark33 » Wed Oct 10, 2012 2:57 pm UTC

Is it like the idea i had a long time ago?

An electric engine that powers a turbine with enough power to keep the engine going, thus creating an infinite energy cycle?
or is it better?

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Re: 1119: "Undoing"

Postby Someguy945 » Wed Oct 10, 2012 3:36 pm UTC

Pfhorrest wrote:I'd make an argument that as stars are fused by gravity, everything is really gravity-powered, but I'll leave that for another day.


Gravity can only pull things together if they have previously been pulled apart, right?

Could we say that everything is really Big Bang powered? That seems like a logical conclusion anyway.

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Re: 1119: "Undoing"

Postby DarkSmokePuncher » Wed Oct 10, 2012 4:05 pm UTC

This only works in 2D. In reality wind direction varies so the fan would have to reposition itself around the turbine to counteract* the latter's effect.

* Yes, yes, not completely. Thermodynamics and all that.

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Re: 1119: "Undoing"

Postby Daggoth » Wed Oct 10, 2012 4:19 pm UTC

What if we used more power?

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Re: 1119: "Undoing"

Postby Vroomfundel » Wed Oct 10, 2012 4:26 pm UTC

Someguy945 wrote:
Pfhorrest wrote:I'd make an argument that as stars are fused by gravity, everything is really gravity-powered, but I'll leave that for another day.


Gravity can only pull things together if they have previously been pulled apart, right?

Could we say that everything is really Big Bang powered? That seems like a logical conclusion anyway.


We're getting into deep water here. What's pulling matter apart is not the big bang itself but the expansion of the universe, so it's more like cosmological-constant-powered.

Gravity is quite fundamental though - apart from all the energy directly or indirectly derived from the sun (most of what we use - generated by fusion, caused by gravity) and tidal power (directly caused by gravity) we can also tap into the heat of the earth's mantle - which is also powered by gravity, and there is probably liquid water elsewhere in the solar system that's been warmed up by this force alone.

This whole cycle will be broken when we start producing fusion power on an industrial scale - it will get kick-started by some of the conventional sources (gravity-powered) but once running it will be a self-sustaining chain reaction and it will probably be the first time in the history of the universe that energy is produced that isn't caused by gravity.
That's so exciting - how can people be against that, just because it's nuclear and thus supposedly risky? Give people 2 nuclear disasters and they are all like "oh, nuclear power is not good" - and it's all taken less than a hundred thousand lives. For comparison - 1 million people die on the roads per year and I don't see anyone protesting for banning cars because they are dangerous. But for the uneducated, un-thinking public one big disaster > many small disaster. That's what I don't like about democracy - when you are in a minority you're screwed and you need to wait for your fusion power to be produced with meager funding for generations.
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Re: 1119: "Undoing"

Postby mcdigman » Wed Oct 10, 2012 4:58 pm UTC

Vroomfundel wrote:1 million people die on the roads per year and I don't see anyone protesting for banning cars because they are dangerous.


Of course not. But you do see people advocating banning drivers. Seriously-the drunk driving problem disappears completely if the cars are driven by computers, because computers don't drink/text and drive (perhaps excepting Bender from Futurama) and don't get sleep deprived or road rage. Forget whether driverless cars should be legal: the question is whether cars with drivers should be legal.

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Re: 1119: "Undoing"

Postby harperska » Wed Oct 10, 2012 5:03 pm UTC

Pfhorrest wrote:The sun of course is fusion-powered, and fusion is the source of the fissionable materials that power nuclear power plants. So really, every power source is some indirect form of fusion.

I'd make an argument that as stars are fused by gravity, everything is really gravity-powered, but I'll leave that for another day.


While the uranium used in nuclear power plants didn't come from normal solar fusion, I suppose it was technically fusion that created it in an ancient supernova whose remnant eventually became our solar system. Likewise with the radioactive elements whose decay heat keeps the core and mantle of our earth molten allowing for geothermal power. Then again, that supernova was a result of gravity, so the gravity theory still holds.

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Re: 1119: "Undoing"

Postby bmonk » Wed Oct 10, 2012 5:24 pm UTC

Primis wrote:I thought about that for a watermill once, but the conservation of energy make my head hurt

Escher got away with it in his "Waterfall".
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Re: 1119: "Undoing"

Postby kfitch42 » Wed Oct 10, 2012 5:31 pm UTC

This reminds me of a story I read a while ago about a company in Europe (I think it was France) that was shining lamps (fossil fuel powered) on photovoltaic cells in order to get subsidies or tax credits. Supposedly they were able to make money this way.

Can't find a link, my google-foo is failing me right now, sorry :(.

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Re: 1119: "Undoing"

Postby tomintx » Wed Oct 10, 2012 6:47 pm UTC

mcdigman wrote: Seriously-the drunk driving problem disappears completely if the cars are driven by computers, because computers don't drink/text and drive

Of course we would see a new definition of "Computer Crash"

Whose fault is it if your driverless car runs thru a group of children crossing the road?

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Re: 1119: "Undoing"

Postby yellow103 » Wed Oct 10, 2012 7:25 pm UTC

Shouldn't a wind farm work by a whole bunch of fans creating wind? And the wind sucking in surrounding air to make more wind? Also, solar powered fans push air to dimmer areas with wind farms. And does "undoing" remind anyone of solving algebra equations?


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