FALLACIES, FALLACIES, FALLACIES...

[Matuchkin]

10 hours ago, KerbonautInTraining said:

The other day I heard some people in my class (including the science teacher) talking about space elevators... need I say more?

Yeah, I really don't think space elevators are going to work out. I'd rather strap a payload to a rocket than go through that business.

[SSgt Baloo]

Space elevators are dangerous. Being exposed to that music for hours on end, waiting to get to the top, is bound to induce narcolepsy.

[Stargate525]

7 hours ago, DolphinDude3 said:

I'm beginning to wonder if the people who write textbooks actually know a single thing about what they're talking about, because from my experience (and apparently yours aswell) they don't.

They don't. Well, the executives in charge of editing don't. Most of the content is cribbed from other textbooks, which is cribbed from other textbooks, ad infinum. It's collated by underpaid -insert field here- majors (if you're lucky; if you're not, it's generic english-degree interns). Fact checking isn't cost effective, and it is EXTREMELY rare that anyone who could reasonably be deemed an expert in the field has touched a k-12 grade textbook, because they don't make money and aren't seen as prestigious.

History textbooks are especially rife with this, making facts up whole-cloth in some instances in order to provide narrative, applying the popular politics of the day to past events (seriously, John Brown is either an anti-slave hero or a deranged lunatic depending on the date the book was published), and glorifying American actions so much it borders on the jingoistic. I have no reason to believe that science textbooks would be immune to similar issues (seeing all the crap about the carbon cycle in my local school's newest one is a good example).

[nobodyhasthis2]

Oh here we go

12 hours ago, KerbonautInTraining said:

The other day I heard some people in my class (including the science teacher) talking about space elevators... need I say more?

6 hours ago, KerbonautInTraining said:

They were talking about how you'd go about building it, saying stuff like "oh just start at the top and hang it from the space station" and all throughout they were implying that rockets simply lift their payload straight up, but I don't blame them for that at all. I had no idea what rockets did after going above the clouds until I played KSP, less than a year ago

2 hours ago, Matuchkin said:

Yeah, I really don't think space elevators are going to work out. I'd rather strap a payload to a rocket than go through that business.

Did anyone else see that mistake in assuming you can't get to orbital velocity by going straight up. You can. Ironically the maths comes from the very same source as the rocket equation. Konstantin Tsiolkovsky. The problem is the weight of the space elevator. Tsiolkovsky originally assumed a structure supported by compression. However this is unlikely. All efforts have centered around tensile concepts. The trouble is the longer the tower gets the heavier it gets. To the point where it snaps. That caused quite a bit of speculation on what type of material could be used. Then last year Penn Sate University came up with a method of making DNT. https://en.wikipedia.org/wiki/Carbon_nanothread. This year a simulation indicated that the strength of the material was not a function of its length. Now does this mean buck rogers space elevators. No but it does mean more homework is required here. NASA still has a prize waiting for the answers. http://www.nasa.gov/offices/oct/early_stage_innovation/centennial_challenges/tether/

 

Edited January 31, 2016 by nobodyhasthis2

[Camacha]

6 hours ago, Hcube said:

1)capsules during re-entry are slowed down by the friction of the air 

I assume you are confusing slowing down with heating up, right? Friction/drag is how a capsule slows down. People generally think it is how they heat up too, but we know that compression is the defining factor there.

6 hours ago, Hcube said:

2)bicycles are very stable because of the gyroscopic effect of the spinning wheels (wich is totally not possible since the wheels are like 1.5kg each...)

That is not a fallacy, because its true. Gyroscopic forces are contributing factors in the stability of a bike. There are other factors which turn out to be more important, sure, but that does not make it false.

[KerbonautInTraining]

27 minutes ago, nobodyhasthis2 said:

Did anyone else see that mistake in assuming you can't get to orbital velocity by going straight up. You can.... Tsiolkovsky originally assumed a structure supported by compression. However this is unlikely. All efforts have centered around tensile concepts.

Yeah, but it would have to stretch well beyond geostationary altitude. As I said, the ability to pop things into orbit 35,000km above the earth would be absolutely amazing. TLI from there would be in the order of hundreds of meters per second as opposed to 3.2km/s from LEO.

[Hcube]

2 hours ago, Camacha said:

I assume you are confusing slowing down with heating up, right? Friction/drag is how a capsule slows down. People generally think it is how they heat up too, but we know that compression is the defining factor there.

That is not a fallacy, because its true. Gyroscopic forces are contributing factors in the stability of a bike. There are other factors which turn out to be more important, sure, but that does not make it false.

Yes, i have confused heating up and slowing down; and i will edit that. I actually checked the book and it mentions both slowing down and heating up... However the compression is also a factor for the slow down with the surpression in front of the capsule and the depression behind it.

For the bicycle : no, it's always used as an exemple by teachers but the gyroscopic effect is so minuscule that it is wrong to say that it's the reason why the bicycle is stable

[Bill Phil]

3 hours ago, Camacha said:

I assume you are confusing slowing down with heating up, right? Friction/drag is how a capsule slows down. People generally think it is how they heat up too, but we know that compression is the defining factor there.

That is not a fallacy, because its true. Gyroscopic forces are contributing factors in the stability of a bike. There are other factors which turn out to be more important, sure, but that does not make it false.

I'm pretty sure compression slows it down as well. There's an increased pressure region in front of the reentering object, and we know that pressure pushes on things. So forces beyond drag will affect the object. Maybe not quite as much, but the compression does contribute.

[Waxing_Kibbous]

7 hours ago, Hcube said:

For the bicycle : no, it's always used as an exemple by teachers but the gyroscopic effect is so minuscule that it is wrong to say that it's the reason why the bicycle is stable

Most proper science classes have this setup: a platform that spins that somebody can stand on, and a bicycle with two handles to grab onto at the hub. Spin the wheel while standing on the platform, then rotate it one way, then the other, and get back to me.

[Bill Phil]

1 minute ago, Waxing_Kibbous said:

Most proper science classes have this setup: a platform that spins that somebody can stand on, and a bicycle with two handles to grab onto at the hub. Spin the wheel while standing on the platform, then rotate it one way, then the other, and get back to me.

Well it's also the tendency of the front wheels to stay going forward, even if it leans. This is mainly a result of the geometry.

[cantab]

3 hours ago, Waxing_Kibbous said:

Most proper science classes have this setup: a platform that spins that somebody can stand on, and a bicycle with two handles to grab onto at the hub. Spin the wheel while standing on the platform, then rotate it one way, then the other, and get back to me.

I've tried something similar - but the bicycle wheel in question was weighted with a chain fixed round the rim.

As others have alluded to, bicycle stability is complicated, but for "typical" bicycle designs the gyroscopic forces are not the primary factor. To say that gyroscopic forces help keep a bike upright is true, to imply that they're the only reason it stays upright is false.

For another example of schools teaching incorrect things: throughout chemistry at school (when everyone has to study it) and even in sixth form (when only people who choose it study it) it was drummed into me, "isotopes of the same element behave the same chemically". Then come to university and I'm not even told that's wrong, the courses just start talking about isotopes behaving differently in chemical reactions. Very jarring, it took me unnecessary time and effort to get over that because I'd spent so long being taught an untruth.

[Bill Phil]

3 hours ago, cantab said:

I've tried something similar - but the bicycle wheel in question was weighted with a chain fixed round the rim.

As others have alluded to, bicycle stability is complicated, but for "typical" bicycle designs the gyroscopic forces are not the primary factor. To say that gyroscopic forces help keep a bike upright is true, to imply that they're the only reason it stays upright is false.

For another example of schools teaching incorrect things: throughout chemistry at school (when everyone has to study it) and even in sixth form (when only people who choose it study it) it was drummed into me, "isotopes of the same element behave the same chemically". Then come to university and I'm not even told that's wrong, the courses just start talking about isotopes behaving differently in chemical reactions. Very jarring, it took me unnecessary time and effort to get over that because I'd spent so long being taught an untruth.

Isotopes are changes in the atomic mass, with a change in the neutron number. Are you sure you're not confusing isotope with ion in this case? Isotopes shouldn't behave differently. A good amount of the water you drink has the deuterium isotope of hydrogen in it, which reacted the exact same way.

Granted, the mass is different, which can change a few things around, but it seems highly unlikely.

[StrandedonEarth]

45 minutes ago, Bill Phil said:

Isotopes are changes in the atomic mass, with a change in the neutron number. Are you sure you're not confusing isotope with ion in this case? Isotopes shouldn't behave differently. A good amount of the water you drink has the deuterium isotope of hydrogen in it, which reacted the exact same way.

Granted, the mass is different, which can change a few things around, but it seems highly unlikely.

Exactly what i thought too. OTOH, I once read a short mystery story where the basic premise was that the human body can't use heavy water. Granted, it's fiction, so I don't know how true that is. A woman who drank nothing but bottled water was murdered when her not-so-loving hubby secretly replaced her jugs of drinking water with pure heavy water. The coroner was baffled when the body was bloated with water but the apparent cause of death was dehydration.

[cantab]

3 hours ago, Bill Phil said:

Granted, the mass is different, which can change a few things around, but it seems highly unlikely.

It does change things around. Mainly it's kinetic effects - the different isotopes form the same compounds but the rates of reaction are slightly different. This means that chemical reactions and biological processes can "prefer" one isotope to another, which in turn means that precisely measuring isotopic ratios of a sample can tell us about its history. For example the isotope ratios of oxygen in the calcite shells of Foraminifera depend on the ocean temperature, and this allows geoscientists to learn about Earth's climate history.

In some cases, especially hydrogen, the effects are more dramatic. Bonds can be stronger or weaker depending on the isotopes. That, combined with the importance of hydrogen bonds and water in living things, is why heavy water is poisonous in large doses (as in a significant fraction of your total fluid intake).

[Bill Phil]

10 hours ago, cantab said:

It does change things around. Mainly it's kinetic effects - the different isotopes form the same compounds but the rates of reaction are slightly different. This means that chemical reactions and biological processes can "prefer" one isotope to another, which in turn means that precisely measuring isotopic ratios of a sample can tell us about its history. For example the isotope ratios of oxygen in the calcite shells of Foraminifera depend on the ocean temperature, and this allows geoscientists to learn about Earth's climate history.

In some cases, especially hydrogen, the effects are more dramatic. Bonds can be stronger or weaker depending on the isotopes. That, combined with the importance of hydrogen bonds and water in living things, is why heavy water is poisonous in large doses (as in a significant fraction of your total fluid intake).

That's caused by the mass difference. The collision effects are changed as well, I assume? The compounds should be identical chemically, though. Unless there's other elements and compounds in the way. 

[KerikBalm]

Wikipedia to the rescue:

Physical properties

The physical properties of deuterium compounds can exhibit significant kinetic isotope effects and other physical and chemical property differences from the hydrogen analogs. D₂O, for example, is more viscous than H₂O.^[14] Chemically, there are differences in bond energy and length for compounds of heavy hydrogen isotopes compared to normal hydrogen, which are larger than the isotopic differences in any other element. Bonds involving deuterium and tritium are somewhat stronger than the corresponding bonds in hydrogen, and these differences are enough to cause significant changes in biological reactions.

Deuterium can replace the normal hydrogen in water molecules to form heavy water (D₂O), which is about 10.6% denser than normal water (so that ice made from it sinks in ordinary water). Heavy water is slightly toxic in eukaryotic animals, with 25% substitution of the body water causing cell division problems and sterility, and 50% substitution causing death by cytotoxic syndrome (bone marrow failure and gastrointestinal lining failure). Prokaryotic organisms, however, can survive and grow in pure heavy water, though they develop slowly.^[15] Despite this toxicity, consumption of heavy water under normal circumstances does not pose a health threat to humans. It is estimated that a 70 kg person might drink 4.8 liters of heavy water without serious consequences.^[16] Small doses of heavy water (a few grams in humans, containing an amount of deuterium comparable to that normally present in the body) are routinely used as harmless metabolic tracers in humans and animals

 

As to the moon being a planet, their argument was bad, but maybe they just didn't explain the arguments well. An argument can be made for considering Earth-Moon as a double planet system - as one might consider Charon a planet if Pluto was also considered a planet, as its considered a double (dwarf) planet.

from within the Earth–Moon system, the simplest way of picturing the situation is to have the Moon revolve about the Earth; but if you were to draw a picture of the orbits of the Earth and Moon about the Sun exactly to scale, you would see that the Moon's orbit is everywhere concave toward the Sun. It is always "falling toward" the Sun. All the other satellites, without exception, "fall away" from the Sun through part of their orbits, caught as they are by the superior pull of their primary planets – but not the Moon.^{[5][6][Footnote 1]}

— Isaac Asimov

[nobodyhasthis2]

On 1/31/2016 at 6:50 PM, cantab said:

As others have alluded to, bicycle stability is complicated, but for "typical" bicycle designs the gyroscopic forces are not the primary factor. To say that gyroscopic forces help keep a bike upright is true, to imply that they're the only reason it stays upright is false.

 

To imply that they're the only reason it stays upright is not only false. It is delusional 

Edited February 2, 2016 by nobodyhasthis2

[BloodDusk]

I fail to see the relation between the OPs thread and the Topic's title.

[Matuchkin]

2 hours ago, BloodDusk said:

I fail to see the relation between the OPs thread and the Topic's title.

We're talking about annoying fallacies and mistakes usually done by people, especially people who insist they're correct.

Have fun. 

[BloodDusk]

1 hour ago, Matuchkin said:

We're talking about annoying fallacies and mistakes usually done by people, especially people who insist they're correct.

Have fun. 

Isn't this essentially the entirety of the Internet?

[Matuchkin]

16 hours ago, BloodDusk said:

Isn't this essentially the entirety of the Internet?

Then let it be the entirety of the internet. We can just have our own KSP forum section for it. Why not?