Interesting findings on the internet

[mnementh]

Thanks. I stand corrected. While I still find it hard to believe we can actually be sortof getting something for nothing given ...

We aren't, of course.

Neither are we when we have heat pumps that are more than 100% efficient.

Nor are when, as implemented in 1238AD and patented over 200 years ago, a stream of water at one hydraulic pressure (i.e. head) can be used output water at a higher hydraulic pressure - i.e. effectively water flowing uphill. Apparently there were 3 such devices in use about 5 miles from me, until mains water arrived in 1958 - and a farm continued to use theirs for livestock well into the 60s.

There was even a variant that managed to achieve that with no moving parts, raising water 110ft for irrigation.
https://npgallery.nps.gov/NRHP/GetAsset ... 00631_text

I am indirectly reminded of one of my favourite "something for nothing" machines - the Kelvin water dropper electrostatic generator.



If I had a natural source of constant running water in my garden I think I'd build one, perhaps run a little electric fence off it complete with warning spark discharges.

Wow! A "glug circuit" with actual glugs!!!

I followed that rabbit-hole for a wee bit today... found this essay from a few years ago on making one with "more power... waugh-waugh-waugh":

https://essay.utwente.nl/68015/1/Knapen_MA_EEMCS.pdf

It's full of lots of scary maths and even equivalent electronic schematics, and the phrase "Pressure-driven Ballistic Kelvin’s Water Dropper" no less.

Should be quite the interesting read for those with a head for the maths.

mnem

[Specmaster]

Here is one of many videos from YT which actually shows this Kelvin Water Dropper in action.

https://www.youtube.com/watch?v=sArNxGnYhNU

[mnementh]

Don't believe it. Sounds like "The LHC will create a mini-black hole", "5G makes us sick", "if you go faster than 40mph all the air will be sucked out the railway carriage", and similar.

But convince me otherwise: numbers and derivations please, but no adjectives.

Compare and contrast the numbers with the understood and demonstrated effects of plate tectonics and tidal friction between the earth and the moon.

Your argument sounds like all the usual head-in-the-sand that brought us to this point; we're all smart enough here to realize that the laws of thermodynamics don't give a flying fuck if we believe in them. The fact we haven't studied this in any material manner is the problem; not whether or not what I've just described is really happening. By definition it has to be. The question is just one of how much damage are we doing.

I mean, unless you're really going to argue that Newtonian physics don't apply just because the conversation is inconvenient.

In that vein, please justify your contention by using classic physics to show how the momentum of the planet is changing, including estimating the magnitude of the changes. Compare and contrast with the measured consequences of large earthquakes. I will listen. As per the reasons/examples below, "numbers, not adjectives".

Here's examples of how to do that, by (very) reputable scientists...

A useful general-purpose motto is the tagline of the justly famous site/book which is lauded by all "sides", from "big energy" to "hardcore greens". Numbers, not adjectives. https://withouthotair.com/ which has quaint æsthetics but superb content.

Here's another example of someone knowledgeable applying numbers to classic physics. They make the assumptions, equations and numbers explicit, and come to some disquieting conclusions. https://dothemath.ucsd.edu/ "Using physics and estimation to assess energy, growth, options".

My favourite is how he demolishes economists usual unstated presumption that growth should and can continue indefinitely. Since modern growth is closely associated with growth in energy consumption, he projects the historic energy growth into the future to see what would happen. Treating the earth as a black-body radiator. Both those starting points are valid and justified. The consequence in 400 years time is implausible, therefore the economists' presumptions have to be implausible "Exponential Economist Meets Finite Physicist" https://dothemath.ucsd.edu/2012/04/econ ... physicist/

And right up our street is his (new) textbook "Energy and Human Ambitions on a Finite Planet; Assessing and Adapting to Planetary Limits" https://escholarship.org/uc/item/9js5291m

Looks like I have found some new fireside/bedtime reading; excellent

So, after looking into this a wee bit... it appears the answer is a "it's not that simple" referring to both assertions; mine and the grossly over-simplified answer presented on Quora. According to what I've read the two are not separate; wind is created both by how the atmosphere is warmed unevenly and by the rotation of the earth (which is also a large part of why it is warmed unevenly, along with the tilt of the planet, its elliptical orbit and a few other factors), to which the atmosphere is coupled by fluid dynamics (Friction and Coriolis effect) .

So yes, some of the energy we're tapping into with wind power has to come from the rotation of the earth... but how much is definitely considerably less than I assumed in my grossly oversimplified understanding of the machine involved. Probably statistically insignificant; but I have no idea how in the hell one would even start constructing a valid model. I'm not a scientist; I don't see a need for me to do so. All I need do is adjust my own apprehension to be more in line with reality.

It's another hugely complex system (global meteorology); we may not fully understand all the intermeshing bits thereof in my lifetime, and certainly not able to reduce it all to an explanation that I could in any way grok fully. I suppose by the time we do, and therefore have perfect forecasting of the weather, we'll probably also have the means to control the weather.

As to how that could affect the rotation of the earth... the load would have to become strong enough to affect the whole system, which is held in a status-quo by those gravitic forces holding earth, sun & moon in their orbits... of which my poor understanding is that they are "strong ties, but somewhat elastic"; it is the latter which makes it possible for our elliptical orbit to be maintained. I cannot even begin to guess how much load that would need to be. Again; no idea how in the hell one would even start constructing a valid model.

I probably guessed it was much less than it is; mostly because I remember growing up in a time when the basic assumption was that "humanity is but a flea on the back of the Earth; we cannot possibly do anything to really affect her" and seeing firsthand just how wrong that assumption is.

I've started reading "Human Ambitions on a Finite Planet"; it's pretty startling how many ways and in what measure humanity is grossly wasteful of the resources Gaia has provided us; worse than I assumed, and I'm pretty pessimistic.

mnem
I learned something; today was not a waste.

[Specmaster]

So, after looking into this a wee bit... it appears the answer is a "it's not that simple" referring to both assertions; mine and the grossly over-simplified answer presented on Quora. According to what I've read the two are not separate; wind is created both by how the atmosphere is warmed unevenly and by the rotation of the earth (which is also a large part of why it is warmed unevenly, along with the tilt of the planet, its elliptical orbit and a few other factors), to which the atmosphere is coupled by fluid dynamics (Friction and Coriolis effect) .

So yes, some of the energy we're tapping into with wind power has to come from the rotation of the earth... but how much is definitely considerably less than I assumed in my grossly oversimplified understanding of the machine involved. Probably statistically insignificant; but I have no idea how in the hell one would even start constructing a valid model. I'm not a scientist; I don't see a need for me to do so. All I need do is adjust my own apprehension to be more in line with reality.

It's another hugely complex system (global meteorology); we may not fully understand all the intermeshing bits thereof in my lifetime, and certainly not able to reduce it all to an explanation that I could in any way grok fully. I suppose by the time we do, and therefore have perfect forecasting of the weather, we'll probably also have the means to control the weather.

As to how that could affect the rotation of the earth... the load would have to become strong enough to affect the whole system, which is held in a status-quo by those gravitic forces holding earth, sun & moon in their orbits... of which my poor understanding is that they are "strong ties, but somewhat elastic"; it is the latter which makes it possible for our elliptical orbit to be maintained. I cannot even begin to guess how much load that would need to be. Again; no idea how in the hell one would even start constructing a valid model.

I probably guessed it was much less than it is; mostly because I remember growing up in a time when the basic assumption was that "humanity is but a flea on the back of the Earth; we cannot possibly do anything to really affect her" and seeing firsthand just how wrong that assumption is.

I've started reading "Human Ambitions on a Finite Planet"; it's pretty startling how many ways and in what measure humanity is grossly wasteful of the resources Gaia has provided us; worse than I assumed, and I'm pretty pessimistic.

mnem
I learned something; today was not a waste.

There is still yet another factor where mankind would be making a contribution to the planet's environment, and once again, I like you, aren't a scientist but with all the high-rise buildings we keep erecting, they must also have an impact on the wind strength and also on the earths' rotation as these buildings certainly do catch a lot of wind and that force of the wind hitting them is transmitted straight down into the earths crust and that force could either be helping to speed up, or slow down the rotation. Once again it might only be marginal but one is for sure, the more we build upwards and the more we build, it stands to reason that itself must have some effect on the earth.

[mnementh]

Well, that aspect in particular was a large part of where my apprehension came from; some discussion I'd read some time ago positing that as a possible cause for a measured increase in how fast the earth has been slowing down over the last century-plus, vs the reasonably steady decrease over the last few billion years (supposedly once a day was ~19hours long).

However, in looking for that discussion, I tripped over this recent article claiming the opposite in just the last few years, and positing the Chandler Wobble (variance in the earth's magnetic poles, which I was aware of) and climate change (including slower atmospheric motion ) as potential culprits. Of course, like most such articles, it ends with the usual "it's too soon to tell, but this bears watching" weasel-wording... but evidently the very recent speedup is accepted scientific fact.

https://www.inverse.com/science/why-is- ... ing-faster

mnem
*toddles off to find someplace quiet to have a nap on StarShip Earth*

[Cerebus]

There is still yet another factor where mankind would be making a contribution to the planet's environment, and once again, I like you, aren't a scientist but with all the high-rise buildings we keep erecting, they must also have an impact on the wind strength and also on the earths' rotation as these buildings certainly do catch a lot of wind and that force of the wind hitting them is transmitted straight down into the earths crust and that force could either be helping to speed up, or slow down the rotation.

No. No. No. No. No. No.

For those with the crazy idea that wind somehow has something to do with the earth's rotation, or could somehow affect the earth's rotation I have a question:

Bearing in mind the simple Newtonian creed "For every action there is an equal and opposite reaction" please explain how wind exerts a force on the earth that could speed or slow the earth by pushing against the vacuum of space?

[tggzzz]

There is still yet another factor where mankind would be making a contribution to the planet's environment, and once again, I like you, aren't a scientist but with all the high-rise buildings we keep erecting, they must also have an impact on the wind strength and also on the earths' rotation as these buildings certainly do catch a lot of wind and that force of the wind hitting them is transmitted straight down into the earths crust and that force could either be helping to speed up, or slow down the rotation.

No. No. No. No. No. No.

For those with the crazy idea that wind somehow has something to do with the earth's rotation, or could somehow affect the earth's rotation I have a question:

Bearing in mind the simple Newtonian creed "For every action there is an equal and opposite reaction" please explain how wind exerts a force on the earth that could speed or slow the earth by pushing against the vacuum of space?

There is a mechanism by which both the atmosphere and ocean interact with the earth and its rotation, most visibly manifested in the form of Coriolis forces. Basically as the wind/water moves between the equator and poles, there is a 1000mph change in its speed - with corresponding change in its momentum.

Note that is a much much much larger change in momentum (both mass and speed) than could be caused by any plausible number of windmills. If someone doubts that, let them

• define the proportion of the atmosphere that would be "intercepted" by a windmill; hint: miniscule
• compare the speed change with 1000mph; hint: small
• compare the mass of the air intercepted by a windmill with the mass of the water in the global thermohaline circulation; hint: miniscule

Changes in the global thermohaline circulation, especially the Gulf Stream and AMOC, might have a visible effect - and there are disputed signs that changes are already occurring.

[mnementh]

C... we've been over this and realized that while it's all interconnected in a pretty complex way, the "load" presented is probably orders of magnitude too small to actually affect the rotation of the earth in a meaningful way. You're a little late to the pooh-pooh party; I've already admitted I was wrong.

All we've been discussing today is how I arrived at that misapprehension, and how I've corrected it. At least to my own satisfaction; "probably orders of magnitude too small" is sufficient to me to adjust my apprehension and move on with my life.

As for "pushing against the vacuum of space"...? Ummm...? No; never ever thought or suggested that.

mnem
*toddles off to do something constructive*

[Cerebus]

C... we've been over this and realized that while it's all interconnected in a pretty complex way, the "load" presented is probably orders of magnitude too small to actually affect the rotation of the earth in a meaningful way. You're a little late to the pooh-pooh party; I've already admitted I was wrong.

All we've been discussing today is how I arrived at that misapprehension, and how I've corrected it. At least to my own satisfaction; "probably orders of magnitude too small" is sufficient to me to adjust my apprehension and move on with my life.

As for "pushing against the vacuum of space"...? Ummm...? No; never ever thought or suggested that.

mnem
*toddles off to do something constructive*

I was responding to the ridiculous notion that tall buildings would, via the medium of the wind pressing against them, alter the rate of spin of the earth. For that to happen the thing providing force to the wind has to push against something else that isn't some other bit of the earth, which would require it to push against space.

[Cerebus]

There is a mechanism by which both the atmosphere and ocean interact with the earth and its rotation, most visibly manifested in the form of Coriolis forces. Basically as the wind/water moves between the equator and poles, there is a 1000mph change in its speed - with corresponding change in its momentum.

Lest anyone get the wrong end of the stick here and think you're offering support for gravity interacting with the wind, Coriolis forces are (1) a natural outcome of a rotating reference frame, (2) entirely contained within the earth's self-contained physical system, (3) nothing to do with gravity, (4) entirely powered by solar energy.

[mnementh]

I'll take exception to 2 and 3 - as the gravitic interplay between earth, moon and sun is the engine which causes the spin of the earth, and powers the Coriolis effect. Now yes, the entirety of our atmosphere is a tiny thin little skin on the surface of the planet... but there still is mass there, and therefore inertia. But it does have to be tiny in reference the mass of our planet, and therefore, as I said, must be much less interaction than I originally supposed.

Yes, that is still entirely solar power; something I've said many times already. It's hard to imagine that kind of relationship when you see the awesome amounts of energy present in our weather, and how incredibly far it seems to outer space... you'd think there's just no way all that energy can't affect the planet. Such is the huge difference in scales we're talking aboot.

Now when we place that in the moving frame of reference of our unremarkable little solar system circling around the center of our galaxy, which itself is a part of our local group, which is a part of the Virgo Supercluster... and how all that interacts... that's when my heads starts to go 'splodey.

Yeah, I'm bad at math.

mnem

[Specmaster]

Bearing in mind the simple Newtonian creed "For every action there is an equal and opposite reaction" please explain how wind exerts a force on the earth that could speed or slow the earth by pushing against the vacuum of space?

As I said, I'm no scientist, but it simply struck me that if you take a ball and suspend it in a fashion that would allow it to spin about its axis. Then stick a small pin in it, on the side of the ball and attached a strip of paper or similar, just a mm or so high at right angles to the ball's surface, then simply blowing on it, the ball would indeed rotate gently in the direction of the air flow.

The theory of "For every action there is an equal and opposite reaction" does not stack up in that example, neither does it in other forms of motion, i.e, our cars for example, how come we can get our cars to move when we apply a force to the wheel? Why doesn't the car remain stationary then?

[mnementh]

Oh, that one is simple; Your thought experiment is incomplete: You have to imagine your little ball (and all its atmosphere) suspended in a vacuum. Now... what's blowing on that little pin?

Think more along the lines of the workings of a automotive torque converter, and the fluid coupling inside. Effectively the space around it is outside the sphere of influence of the fluid inside. And that impeller half driven via gravitic "belt" powered by the sun. That's a little closer.

mnem
*back to the grind*

[tggzzz]

I'll take exception to 2 and 3 - as the gravitic interplay between earth, moon and sun is the engine which causes the spin of the earth

Some planets have essentially no spin, in some the spin is retrograde, in some the spin axis is at 90 degrees.

I think you'll find the earth's spin is a consequence of the rotation of the dust clouds around the proto-sun, back when the solar system was forming. Big collisions are the probable cause of "displaced axis" and retrograde spin.

However, the tidal forces are causing the earth's spin to reduce, increasing the length of the day by about 2ms every century. Earth's reduced angular momentum means, according to wackypedia, that the earth is losing energy at the rate of 3.7TW with most of it being transferred (via friction/viscosity) to the atmosphere and oceans. https://en.wikipedia.org/wiki/Tidal_acceleration

[Specmaster]

Oh, that one is simple; Your thought experiment is incomplete: You have to imagine your little ball (and all its atmosphere) suspended in a vacuum. Now... what's blowing on that little pin?

Think more along the lines of the workings of a automotive torque converter, and the fluid coupling inside. Effectively the space around it is outside the sphere of influence of the fluid inside. And that impeller half driven via gravitic "belt" powered by the sun. That's a little closer.

mnem
*back to the grind*

Except, that while Earth may well be in a vacuum, but the Earth itself has an atmosphere and in that, there are winds, yes those winds do not always blow in the same direction, the interaction of those winds on tall buildings must have some effect on the planet it is going to be so small admittedly that we may not be able to measure it.

[mnementh]

Oh, that one is simple; Your thought experiment is incomplete: You have to imagine your little ball (and all its atmosphere) suspended in a vacuum. Now... what's blowing on that little pin?

Think more along the lines of the workings of a automotive torque converter, and the fluid coupling inside. Effectively the space around it is outside the sphere of influence of the fluid inside. And that impeller half driven via gravitic "belt" powered by the sun. That's a little closer.

mnem
*back to the grind*

Except, that while Earth may well be in a vacuum, but the Earth itself has an atmosphere and in that, there are winds, yes those winds do not always blow in the same direction, the interaction of those winds on tall buildings must have some effect on the planet it is going to be so small admittedly that we may not be able to measure it.

Ehhh.... more like vanes of that torque-converter passing through areas of foam vs liquid (high-pressure areas vs low-pressure areas, and the ATF is the "atmosphere"). And some of the vanes are longer than others.

The only place you'll "feel" it is in minute variations in the inertial reaction on the "belt".

mnem
Also an imperfect model. Just a more down-to-earth one that popped into my head on a moment's notice.

[Cerebus]

Bearing in mind the simple Newtonian creed "For every action there is an equal and opposite reaction" please explain how wind exerts a force on the earth that could speed or slow the earth by pushing against the vacuum of space?

As I said, I'm no scientist, but it simply struck me that if you take a ball and suspend it in a fashion that would allow it to spin about its axis. Then stick a small pin in it, on the side of the ball and attached a strip of paper or similar, just a mm or so high at right angles to the ball's surface, then simply blowing on it, the ball would indeed rotate gently in the direction of the air flow.

The theory of "For every action there is an equal and opposite reaction" does not stack up in that example, neither does it in other forms of motion, i.e, our cars for example, how come we can get our cars to move when we apply a force to the wheel? Why doesn't the car remain stationary then?

Of course it does. Whatever is blowing the air toward the suspended ball gets pushed backwards. I really don't know where you're coming from with the car thing - did you really never learn basic Newtonian mechanics at school?

[Cerebus]

I'll take exception to 2 and 3 - as the gravitic interplay between earth, moon and sun is the engine which causes the spin of the earth,

Where did you learn this? It's not right.

Just try Googling "Why does the Earth spin?" - https://www.sciencefocus.com/space/why- ... arth-spin/

The earth spins because it has always spun from when it was first formed because the material that formed it had spin and there's nothing to significantly slow it down given that it's rotating in a vacuum (It has a current angular momentum of approximately 7.2 × 10^33 Kg m^2 s-1 - that is a huge, massive, gargantuan number). Uranus spins at 90 degrees to its orbit, if planetary spin is powered by gravitic interaction with the Sun how can Uranus do that? Compare to Earth at 23.4 degrees.

There are gravitic effects that bleed off a tiny, tiny, tiny little part of that spin and convert it into heat, mostly in the oceans as they experience tides - the effect on angular momentum is so little that the change in day length is currently 1.7ms/century and that figure has changed both up and down over time. That the energy necessary to generate the tides across the whole of the earth only bleeds off 1.7ms per day per century ought to give you the faintest idea how truly massive the angular momentum of the Earth is. If we extracted 0.1% of the whole Earth's tidal energy by harvesting it with turbines we'd slow the Earth by an additional 1.7us per day per century.

[mnementh]

C, I'm guessing that he's having trouble wrapping his brain around the idea of the earth/atmosphere being mechanically isolated from the rest of the universe by vacuum, but coupled to each other by fluid dynamics. That's why I presented the concept of a car torque converter with some air in it; something I know Spec has an understanding of.

In this model, the vanes of the rotating impeller will pass through areas of relatively high and low pressure; same as proud spots on the rotating earth earth will pass through areas of high and low pressure (that we perceive as wind) in the atmosphere.

I think it's that different frame of reference of what wind is on a global scale that is not so obvious to him.

mnem
*toddling off to the Discord*

[mnementh]

I'll take exception to 2 and 3 - as the gravitic interplay between earth, moon and sun is the engine which causes the spin of the earth,

Where did you learn this? It's not right.

Just try Googling "Why does the Earth spin?" - https://www.sciencefocus.com/space/why- ... arth-spin/

The earth spins because it has always spun from when it was first formed because the material that formed it had spin and there's nothing to significantly slow it down given that it's rotating in a vacuum (It has a current angular momentum of approximately 7.2 × 10^33 Kg m^2 s-1 - that is a huge, massive, gargantuan number). Uranus spins at 90 degrees to its orbit, if planetary spin is powered by gravitic interaction with the Sun how can Uranus do that? Compare to Earth at 23.4 degrees.

There are gravitic effects that bleed off a tiny, tiny, tiny little part of that spin and convert it into heat, mostly in the oceans as they experience tides - the effect on angular momentum is so little that the change in day length is currently 1.7ms/century and that figure has changed both up and down over time. That the energy necessary to generate the tides across the whole of the earth only bleeds off 1.7ms per day per century ought to give you the faintest idea how truly massive the angular momentum of the Earth is. If we extracted 0.1% of the whole Earth's tidal energy by harvesting it with turbines we'd slow the Earth by an additional 1.7us per day per century.

Yeah, you're right. Where I got that from was discussion of theories as to why this machine has kept going for so long that were popular when I was young and have since been debunked. *sigh* It sucks finding out that what you "know" has been "known better than" for decades.

mnem
I think I'm just gonna go crawl back into my cave and pull the rocks in behind me.

[Zenith]

As I understand it, in the early days the moon was much closer and pulled the earth. Tides on early earth were huge. Things changed and now the earth pulls the moon. The earth's rotation slows by 1/125th second per century. The moon gains orbital energy and moves 3 cm further away each year. Having a comparatively massive moon stabilises the earth's axis and limits the amount of wobble, which is a good thing as far as advanced life is concerned.

When it comes to the Fermi Paradox - why no sign of other advanced life in the universe? - I'm inclined to go with the Rare Earth hypothesis, partly because we have a massive single moon.

[Cerebus]

As I understand it, in the early days the moon was much closer and pulled the earth. Tides on early earth were huge. Things changed and now the earth pulls the moon.

They both pull each other, that's how gravity works - it creates a force between two masses that is proportional to the product of their masses and inversely proportional to the square of the distance between them.

When it comes to the Fermi Paradox - why no sign of other advanced life in the universe? - I'm inclined to go with the Rare Earth hypothesis, partly because we have a massive single moon.

One person, I forget who, said that if interstellar travel was practical then we'd already know because earth would be a tourist attraction. Why? How rare is a planet that has a moon just the right size to just fit over the sun during a total solar eclipse? So, if interstellar travel was practicable every total solar eclipse there would be hoards of aliens amoungst the crowds of humans watching the eclipse.

[mnementh]

How do we know there aren't? We can't even do an accurate head count when our lives literally depend on it.

mnem
*toddles off to school widda chiddlers*

[Cerebus]

C, I'm guessing that he's having trouble wrapping his brain around the idea of the earth/atmosphere being mechanically isolated from the rest of the universe by vacuum, but coupled to each other by fluid dynamics. That's why I presented the concept of a car torque converter with some air in it; something I know Spec has an understanding of.

In this model, the vanes of the rotating impeller will pass through areas of relatively high and low pressure; same as proud spots on the rotating earth earth will pass through areas of high and low pressure (that we perceive as wind) in the atmosphere.

I think it's that different frame of reference of what wind is on a global scale that is not so obvious to him.

mnem
*toddling off to the Discord*

No his problem is summed up in one sentence:

The theory of "For every action there is an equal and opposite reaction" does not stack up in that example, neither does it in other forms of motion

Someone who says the latter clearly has not learned Newtonian mechanics because he has just denied the veracity of Newton's third law of motion.

While all scientific knowledge is consensual and conditional on "unless we learn better in the future" I can think of no law of physics more accepted, less conditional nor more supported by the weight of everyday evidence than Newton's third law. Sure, in the last century or so we've had to qualify it with "unless things are too massive(general relativity), too fast (special relativity) or two small (quantum mechanics)" but it is the most tested and proven law of physics at everyday masses and speeds.

Graham's literally arguing with something that has had universal scientific consensus since relatively shortly after Philosophiæ Naturalis Principia Mathematica was published 336 years ago. There's no way to sugar coat that.


A much simpler analogy to your rather convoluted torque converter one is a garden hose.

When I was a small child I loved playing with the garden hose (I still do). I quickly learned that you could, instead of watering the garden as you'd told dad you would do, push things about with a jet of water (and get told off). A jet of water (a fluid) in no different to a jet of gas (also a fluid) aka wind. I also quickly learned that the jet of water would push the hose backward and that if there wasn't a force applied by hand to deal with that "equal and opposite reaction" the hose would shoot off on its own. The jet has to have something to push back against so that it can push things in front of it. So by about age 5 I had a solid empirical understanding of Newton's 3rd law, as did all the rest of us that played with garden hoses. I was about 12 or 13 before I was formally taught that phenomenon had a name: "Newton's third law of motion" and that it also happened with more rigid things like the floor pushing up to resist my weight.

[Cerebus]

How do we know there aren't? We can't even do an accurate head count when our lives literally depend on it.

mnem
*toddles off to school widda chiddlers*

I'd rather have thought that, looking around any crowd, there are a lot of suspects for the rôle of "Alien Visitor".