CaptainPanic

That's because you ban them. They tend to take that personally.

That's only because you didn't take my friends-exam yet. I'm sure all my friends can see it. Nah, but a monkey wrench might come in handy. You know iodine...

Yes, let's get back on topic: And since the MSDS (Material Safety Data Sheet) says about ammonium fluoride that: According to another source, HF might even form when you expose the ammonium fluoride to water. The same source says that the decomposition already occurs at >100C (which is, imho, a pretty low temperature). As for safety of putting this kind of info on our forum - I just plucked that off the internet. It took me about 10 seconds to find it. The second source is from the manufacturer themselves. I'm sure that if you make millions of pounds per year, you do give it a little thought. Btw, they do not sell it directly to customers, only to industry.

Why can't we be friends? Why can't we be friends? Why can't we be friends? Why can't we be friends?

No, there should be more (way more) emphasis on the application. You don't teach someone how to use a tool without saying what you can build with it. It's like showing how to use a hammer. At first, it seems utterly pointless, like you can only destroy things with a hammer. Students would be bored. And then 2 years later, the school decides to teach them about nails too. And all the students suddenly see the point of a hammer. If they'd just do it simultaneously (it would only require to change the symbols from [math]x[/math] and [math]y[/math] to whatever the symbols are in physics), and if they would synchronize physics classes with maths classes, then it would all make sense to the kids / students. Newton himself did it the right way: 1. Encounter a problem that he could not solve 2. Learn more maths (in his case, he invented it) 3. Solve problem With such a process, step 2 is not such a pointless agony.

Generally, fuel is more expensive in terms of money/energy than electricity from the net. Making your own fuel might solve that, but you have to get a cheap installation. I know that some farmers have a bio-gas installation, connected to a gas engine. They might use the waste heat (and the CO2!!) for their greenhouses, and sell the electricity if they have a surplus. This seems profitable. However, they typically have 2 MW (electric) installations. That is a little large for your backyard. Also, it must be said that most greenhouse farmers just use natural gas in their combined heat and power installations. (Here's an article about Dutch farmers doing this at quite a large scale). So, in summary, it is interesting for farmers because they can use all the products they make: electricity, heat and CO2. Similarly, there are installations called micro-chp. It's an electricity generator that sends the waste heat to the heating system of your house, and sends any surplus of electricity back into the net. I don't see why that wouldn't run on bio-gas. An even smaller scale will suffer from the economy of scale (bigger = better, so smaller = worse)... and there will be a point where it's all just a waste of money. But before shooting down your idea too early - what fuel were you thinking of? Ethanol, biodiesel, bio-gas (methane), pyrolysis oil, something else? And would you have access to some freebies (i.e. do you have an engine and an electricity generator lying around)? Btw, I think that at this moment, solar panels might be your best option. They're relatively cheap at the moment due to an overcapacity in production. That's bad for the industry, but good for consumers like you. Depending on where you live (depending on the electricity price, and how much sunshine you get), I read that they're now economically interesting without subsidies. But this might be considered a thread hijack. Sorry.

It's not a problem if you have some fundamentalists (taliban) in your parliament. However, when you only have two parties, and the fundamentalists find a way to practically hijack every discussion, and hold one of the two parties hostage, you certainly have a problem. Somehow by remaining a part of the republicans, they have an immense power. And the moderate republicans cannot kick them out, because then they'd be certain to lose to the Democrats. The root of the problem therefore is not the Tea Party, or the fact that you have some weird fundamentalists. The real root of the problem is the obsolete two-party system of the USA.

The only time I multitask is when I grab a coffee when I'm waiting at the printer. And even then I often forget the printouts. My productivity peaks when I am totally in the zone. That means: focussed on one task and only one task.

Comparing the beliefs of religious people to Star Trek can come over insulting - because you're saying that religion is "just another story". I agree, but religious people don't. They will read your post, and they will defend their God. And they will say that God exists. Then you will demand proof. Then they ignore your request, because this proof does not exist. Then you ask again. They ignore you again. Then you will report that. Then the mods place a warning, and ultimately have to take more severe action because some religious person is preaching and not responding to questions, because they cannot, because there is no proof. And you know that, I know that, we all know that. Because we've been there before. I only need to link to any random thread in our religion forum. I can pick one blindly, and the discussion would resemble my brief summary. This thread approaches the same old problem from a different angle. To make some stories of really unlikely things to happen in the universe is just equally pointless. All you're saying is: "See, this is how certain I am that god doesn't exist - it would take an actual miracle to convince me". And there you have your answer: A miracle that we can test and verify and test again.

What I meant to say is that math is not a goal in itself. Maths enables you to achieve other goals. Newton developed a lot of maths because he needed it to solve problems he encountered in physics... he didn't develop maths just for the hell of it. I could have left out the word "only", but I deliberately left it in my post for reasons of marketing and promotion of the other fields where you need math.

It would be a funny calculation to find out how long it would take a tug to move an oil tanker of 500,000 ton, if it exerts a force of 5 N. If F = m*a, and F = 5 N, and m = 500,000,000 kg, then: a = F/m = 5/500,000,000 = 0.00000001 m/s2. That would mean that it takes: xt = 0.5*a*t^2, so: t = sqrt(xt/(0.5*a)) = sqrt(1/(0.5*0.00000001))=14142 seconds, or nearly 4 hours. Since in , a tug will need seconds to do that - minutes if they're being careful - we can conclude that the force is severely underestimated. Let's say they need 60 seconds to get it to move... a = 1/(0.5*60^2)=0.0006 m/s2 So: F = m*a = 500,000,000*0.0006 = 277,000 N. (A quick check online for tugs says that this number is closer to the truth than the 5N we had in the assignment). And that is how you take a thread completely off topic. (let's get back on topic, shall we?)

Math is only a tool. It's like saying "I hate hammers"... which I think is a little weird. You can say that you hate carpentry or you hate making furniture, but to hate just one tool specifically is a little strange. In most fields of science and engineering, you will get really comfortable with the maths once you're out of university. The simple reason is that you'll use only one (small?) bit of math all the time - if you use it at all. You'll get so used to it that you'll hardly give it any thought.

Try to describe how you would try to solve this. Yeah, I hate it when teachers are too lazy to look up proper numbers. They could teach students a feeling for numbers at the same time as teaching them the theoretical stuff, but no.

Well, that's a formula for pressure... but in all fairness, I think you'd better study a little more. There is no force (F) given, and no surface area (A) either... so your formula is not exactly useful here.

My first thought was that you may have stepped on it, and it got stuck in the profile under your shoe.

Guys, let's get back on topic, shall we? The OP suggests that in a theoretical case, the earth is flung into space. Nobody cares about Mars (not in this thread at least).

My question is a spin off from another thread about sesame seeds. Phi for All replied, and my reply to him goes too far off topic to keep it in that thread. Do you keep track of such things a lot? Personally I don't keep track of anything at all. I just eat a varied diet, and get my daily weekly exercise, but I am totally unaware of quantities of certain elements in certain foods, and even of the amount of calories (Joules!) that I take in... And I have no idea about the quantities of any of the nutritional categories, like certain elements, proteins, fats, salts or vitamins. I never read the small print on the packaging. For certain elements (manganese, copper) I wouldn't even know how to find out. Google probably? However, I do make conscious choices. Recently, I switched from having some cookies in the evening to having some fruit. Must say that I actually like the taste better, and I guess it's healthier too. My evening meal usually (not always) contains some veggies. And I also measure how much pasta/rice I boil for meals - because when I didn't do that, I always made too much (and ate it too). And the only thing I care about on the packaging is the origin of the food: GMO or not. Locally grown or far away. Fresh or frozen. Fair trade or modern slave labor. What's your dietary masterplan? Do you make conscious choices about anything?

First of all, if your school recommends one particular calculator (TI-84+), that probably means the teachers understand that one the best. Therefore, buying the recommended one means you'll get help easier. It might not be the best calculator around, but it has practical advantages at your particular school. Yeah, I understand that completely. They make such a fuss about the letters, and in maths they never mean a thing! In real life, by now you have worked with that "jumbled mess of letters and numbers" a lot. Without knowing it, you probably got quite experienced with it actually. You will see that once the maths gets applied to a real-life problem, the letters mean something, and you might recognize things quickly... and the reason they use a single letter (instead of whole words) is just laziness. It's quicker to write a single letter. Only in maths classes are the letters without meaning.

I can think of 3 reasons: 1. It is good to eat a variety of foods. So, by putting some other seeds on bread, you add some nutritional value. 2. It looks nice. 3. It tastes nice. I think that options #2 and #3 are gonna be a lot more important than #1. Btw, sesame it is a very tough plant, which will grow on soils where not much else will grow (source: wikipedia). The use of arid land is considered quite important for all our futures. As for the nutritional value: it's quite high in energy (as most seeds and nuts). Have a look at that wikipedia page for more info.

Since this is homework, we don't give straight answers. Which kind of formula do you think you will need? (Either write the formula, or give the name of the formula, if you know it). The more you show us that you tried yourself, the more we will help you.

Excellent question. What matters is that the density of the air is not the same. Here is a table (wikipedia) that gives the relation between the density of the air and the temperature at a pressure of 101.325 kPa, or 1 atm. You can see that the difference in air density between air at +2 C and +30 C is about 10%. If the velocity of the air is the same, if the pressure of the air is the same, and if your kite is the same, then cold air should create a larger force because your kite is catching a larger mass of air per time. However, you should note that the air pressure is not constant! The difference between high pressure days and low pressure days can be almost as large. The pressure is linearly related to the density of air. And air pressure can also easily change 5% between high and low, and even more in extreme cases. Sunny days tend to be high pressure. Cloudy, rainy days tend to be lower pressure, and the lowest pressure occurs in storms (and esp. hurricanes).

It's CO + H2O <--> CO2 + H2 It is called the water gas shift reaction, and it is an equilibrium. To get complete conversion to H2, you need a separation and a recycle. But because your gasification gas is (as I said before) full of other molecules, you will need more (many more) separations before you can send the gas to a fuel cell. And then there is that little issue that a fuel cell is just not a very economical thing.

Not sure. I am a chemical engineer, not an astronomer. If a gas expands, then the molecules will move away from each other - the density is being reduced. But at the same time, they still continuously crash into each other. So, the way I see the expansion, of both a gas and the universe, is that there is an average expansion, but superimposed on that is some random motion. And for objects that are near each other, the movement caused by expansion is (relatively) small, whereas the random motion of two objects would have at least a factor which is no function of the distance between the two objects (and a factor, like gravity, which is). Obviously, this "random motion" comes from somewhere. Could be gravitational interactions that happened in a (distant) past. Why is a gas molecule moving in the direction it is moving? I don't know. But maybe I should stop using that term "random motion". It's a term used in chemistry (also called Brownian motion), not astronomy... I agree that the state of the early universe will have determined where stuff is moving now. Hope I didn't confuse things too much with my analogy with molecules.

If you have a football stadium full of people, and they all go home after the match, individual people can still bump into each other hundreds of meters away from the stadium. On average, everything is moving away from everything else. But individual stars or galaxies can still approach each other. imatfaal - isn't random motion another reason?

First of all, I think that we shouldn't underestimate how much heat is stored in the oceans. You don't just have to cool the surface of the oceans, but a pretty thick layer of water. Cold water will drop, and hot water will rise. This natural convection will keep our atmosphere heated for a while. The surface of the earth typically receives something in the order of 200 W/m2 (annual average, including day and night). So, while we're at normal earth-like tempertures, we also radiate 200 W/m2 into space. Since the most of the earth's surface is water, we can just assume that the specific heat is 3.93 kJ/kgK (*), and the heat of fusion is 334 kJ/kg. If the average ocean is +10C, we need to get rid of 10*3.93*103+ 334*103 = 373.3*103 J/kg. That means that if you just want to cool and freeze the sea up to a depth of 1 meter (1,000 kg/m2), you have to get rid of 373.3*106 J/m2 Since our average radiation is apparently about 200 W/m2, this is estimated to take about 1,866500 seconds (= 22 days). Since our tempertare would drop asymptotically (cooling would slow down), I am guestimating that it would take years/decades before the atmosphere starts to condense into a liquid. We'd all starve long before that. And about the CO2 in our atmosphere - it's just too little to actually freeze out by itself. The concentration is too low, so its (*) Seawater has a lower specific heat than fresh water. Fresh water is 4.18 kJ/kgK.