pavelcherepan

I can't say I'm unbiased in this situation, I'm Russian after all, but I haven't seen any unbiased opinions in this discussion so I don't feel bad about it. Also, I've been living away from Russia for quite a few years now, but still read Russian media as well as English-language media, so it's nice to see both sides of the picture, which, unfortunately, many posters here don't have access to. That opinion is to be expected. Since coming to power in 2000 Putin has been running a somewhat nationalist foreign relations line. And "nationalist" no in a sense of Nazi Germany nationalist, but in a sense of doing what's best for Russia and Russian people in general without much of a regard for everyone else. That's why his approval ratings at home a sky-high, that's why so many people outside of Russia hate him, but for exactly same reasons people around the world dislike US. Well, I don't. I guess, this kind of response was to be expected. Also, the decision to increase airforce numbers has already been made. A few Su-27SMs will be relocated to Syria to escort every single bomber on their missions. This actually worries me a lot. The original batch of pilots were the most experienced and trained guys in the army, so now if with this knee-jerk decision some newbies will make it to Syria, the situation will only get worse. Who knows how an inexperienced fighter pilot can react in a dangerous situation. Also, back in 2012 Turkish F-4 was shot down in Syria after wandering in its airspace to which former prime minister and now president Erdogan said the following: I guess, if we consider all the potential reasons for heated relations between Russia and Turkey we should also include: * Russia supports president Assad, while Turkey wants him gone * Allegedly, Turkey profits from illegal oil imports from IS controlled territories and in recent weeks Russian military has destroyed quite a few oil convoys * Turkey might be interested in spreading its influence over the northern Syria, which is now complicated due to Russian military presence * Assad victory would greatly benefit Iran and Shia Muslim groups, while Turkey supports Sunni rebels And, lastly, this is Middle East and I forgot who said that, but the general idea was that the last European who was able to really understand the actual complex workings in the Middle East was T.E. Lawrence a.k.a. Lawrence of Arabia, but, unfortunately, he's long gone.

There are a lot of things that bother me about this incident, but most of all - why such a high quality video footage became available almost straight away? I don't dismiss the possibility that a film crew just happened to be there when the downing happened and they happened to be filming stuff (in an area where no fighting has been going on), but still it seems rather odd. I think I'll go play Fallout 4. Who knows, knowledge of survival in post-apocalyptic world might come in handy in the near future.

It sort of does from my perspective. If we can measure something and find it infinitesimally small, but not zero we can still approximate it with a zero, but still it can be measured. On the other hand, if we can't measure something, can we describe it with a number? Thanks, studiot, these are good examples. As far as temperature and absolute zero is concerned I'd call it an abstraction, because even if it can be achieved, how do you measure an absolute zero temperature? As for the example with forces, you can say that the object that forces are acting upon experiences no net force as if those didn't exist, yet the system as a whole can be described as having a number of forces that cancel each other. Probably it's more of a philosophy forum question.

I was just thinking, can number zero describe a physical quantity of an object or is it more correct to say that the object doesn't possess that quality? For example, what is more correct: a) neutron has a zero electrical charge or b) neutron doesn't have electrical charge? On one hand, since we can't quantify the value of it's charge, it doesn't have it. Period. On the other hand, neutron is the result of three quarks coming together and they do have charges and the sum of those is 0. In this case it would be rather strange that three entities that possess this quality will combine to form another entity that doesn't. I'm confused.

Yeah, but if you launch straight up and keep going straight up won't you get lateral velocity once you're well and truly out of the atmosphere? Assuming you launch from equator you should get ~460 m/s of lateral velocity, so I solved the same equation but for v=460 m/s (I disregarded the extra 1 mph because it's too small to matter much).

There's some confusion here, I guess. So, he's out of the craft on LEO, travelling anywhere around 7800 m/s and throws the screwdriver at 20 m/s. From my layman understanding of how orbits work and depending on the direction it's thrown the screwdriver will have increased it's orbital velocity and orbital eccentricity (thrown prograde), decreased orbital velocity and increased eccentricity (retrograde), increased orbital velocity and slightly shifted apogee/perigee along the orbit (thrown to/from Earth) or changed inclination slightly (thrown north/south direction). Obviously there's a bajillion of intermediate options. Whatever he does he's unlikely to be able to supply the screwdriver with enough delta-v to hit the planet like very soon. It will just very-very slightly change it's orbital parameters. Anyway, both the astronaut and screwdriver will stay in orbit for a long-long time until their orbits deteriorate enough for re-entry. It was just a guess that astronaut's orbit will deteriorate faster due to drag, but let's do some proper calculations. Let's assume the orbit is 150 km and mostly circular. The orbital velocity is around 7800 m/s. Atmospheric density at this height is around 2.5*10-9 kg/m3 . Body area of an astronaut facing the direction of travel is about 1m2 (with the spacesuit I'll assume something like 1.7m2). Reference area of the screwdriver is somewhere around 0.07 m2. CD for a person is around 1.1 and I'll approximate the shape of the screwdriver with a rectangle with CD of ~0.9. Then by the drag equation: [latex]F_D=1/2\rho*v^2C_DA[/latex] for a person in a spacesuit we get 0.142 N and for the screwdriver we get about 0.00476 N. I used the worst-case scenario, i.e. screwdriver thrown retrograde and it's velocity is now 7780 m/s. Then the deceleration due to drag will be (assuming a person+spacesuit weighs 100 kg and screwdriver 0.3 kg) 0.00142 m/s2 for the person and 0.01586 m/s2 for the screwdriver... which explicitly shows how useless common sense and hunches are when talking physics. I was wrong. The screwdriver will indeed fall first.

Janus, how did you come up with 2.5 trillion miles? I'm getting a very different number around 3.8 million kilometers. Potentially, although maybe not the push to LEO. There are a few things to consider for the flight profile of Shuttle. One is the crew comfort - it's designed so that at no point during the ascent the g-load goes above 3g so that astronauts don't pass out and can react if something goes wrong. The Thrust-to-Weight ratio is another limiting factor during the take-off. Also the Shuttle+EFT+boosters is very awkward aerodynamically so while atmosphere is still present it shouldn't go above a certain acceleration. It might get into space, but it won't go into orbit. There's a lot of space junk that ISS has to evade from time to time. The Earth's atmosphere extends to around 10000 kilometers, so as long as you're below this altitude you'll be getting atmospheric drag. No, the screwdriver would just move to a slightly lower orbit. You would only be able to throw it possibly at ~20 m/s which is a very small adjustment compared to ~7200 m/s LEO velocity. Eventually, after a long-long time, the orbit of the screwdriver will deteriorate and it will fall back to the Earth, but that will take a long time. I rather doubt it. The difference in orbital velocities will be tiny, but your spacecraft will experience way more drag than screwdriver will.

That was not what I had in mind at all. One of the main reasons relativity was developed was that new data on electromagnetism didn't agree with classical mechanics at all. If Newton had known of electromagnetism to the extent Einstein knew, who knows what he would've come up with. That was what I meant. Also it would be rather strange to assume that sort of meaning from that line because in the very nxt sentence I said that Newton's formula stands well in most day-to-day situations as long as you don't need extreme precision. Duh.

I think it was based on empirical data including a lot of work done by Galileo and his own observations and also based on his laws of motion. Based on what was known at the time he got it right. If you don't need an extreme precision you can use Newton's formula to calculate all kinds of stuff with enough accuracy for all day-to-day applications. What in particular are you referring to?

The thing to consider for such a book is that it should be entertaining and captivating as well as educational. An adult can often make a conscious decision to pick up a science book and read it to learn something new, but depending on the age group you're targeting great percentage of kids won't be thrilled about the idea of reading a book that is just pure plain science so you have to trick them into reading it regardless. As for me some of the great childhood memories about science came from Jules Verne's "The Mysterious Island" as well as other his books. If you haven't read it I'd strongly suggest that you do. The story of the book is extremely interesting but at the same time it introduces a lot of science and engineering problems that the group of guys have to solve to be able to survive on a remote island. And not only did they just manage to survive but they went on to build an industrial community with little but their wits about. While in the book itself a lot of science is quite dodgy but basically if I were you I'd write something like it but with more scientific accuracy. Another book to have a look at is Andy Weir's "The Martian" on which the recent box office hit movie is based. This book gives you some very accurate science (mostly) with an extremely engaging story and the best thing about it is that it gives amazing insights on scientific problem solving and makes super-nerdy engineering fun. Hope that helps!

I think that with the case of Columbia NASA management has gone down the road of "If it ain't broke don't fix it". There has been several cases before when there have been foam strikes recorded but they never caused any real damage, hence while it was not something that tiles were designed to survive, it's been considered that no harm can come. Even when during the investigation the experiment was performed NASA management was reluctant to supply tiles to get tested because they were adamant that it was not the cause of the incident. I highly doubt it were possible to organise a resupply mission within the limited time, unless there was already a rocket ready to leave, which there wasn't. On the other hand, if NASA management listened to engineers and allowed to take satellite images of the impacted area some repairs potentially could've been done, although its likely that those wouldn't have saved the shuttle, but at least they could've tried.

What do you mean by "splash height"? At the point of impact and even kilometers away from it the temperature would be so extreme that water would instantly evaporate, hence there'd be no splash. Rather than tsunami being a result of the asteroid splashing into the ocean like a stone creates waves when you throw it in water, it was a result of the seismic event that the impact created. I would say that the number of 5 kilometres refers to the height of tsunami as it hits the shore. Tsunamis are created by a vertical displacement of Earth's crush (also landslides too, but that's not important) so in order to have a 5km tsunami wave somewhere in the open ocean not too far from where it's been created, the vertical movement of the crust would have to be around the same amount - 5 kilometres or more. Normally in the open ocean tsunami waves are only some tens of centimetres high and generally very hard to notice. On the other hand, when such wave approaches the shore the sloping of the sea floor causes it to rise up and that's when you'd have all the huge 50, 250, 500-m high waves. There's also an interesting simulation video on Youtube that shows that whatever happened it's unlikely that the height of the tsunami was more than a 100m. https://www.youtube.com/watch?v=Dcp0JhwNgmE

Well, we DO go forwards in time... like all the time. And we do use XYZT, for example (I think it's Feynman's example), if you want to meet someone, you need to arrange the meeting both in space and time, like "Meet me at the pub at 5 pm". Here's your xyzt.

Maybe Hypothesis is a better word. Please define the term "known Universe". So you're taking genetics'ish approach to particle physics? What about time? Most of all, how is your idea better than the existing ones? Where's the mathematical framework? Any experimental data to support your hypothesis?

If we look at musical voices, lowest frequency male voice is the bass. As the article says, the standard range from this type of voice is beween E2 and E4 which is 82.4-329.6 Hz. For females the deep voice is contralto which is between 174.6-698.5 Hz. I doubt you'll have much luck with that. On average the lowest fundamental frequency for the male voice is about 85Hz. Hence, you're not very likely to find someone who can produce 80 Hz at all.

This still doesn't make sense. The question was about how Earth rotating backwards would affect living things here, not how it will affect the orbit of the Moon, which, even though it will drop lover and eventually be ripped apart by tidal forces, will not happen for hundreds of millions of years.

You can also do C) Guide the light around yourself, for example with a set of mirrors, so that whoever is looking at you will see what's behind you, instead of seeing you. This method works for "magicians" although it can only work from a certain angle.

OK. So as I said before the standard form for the equation of a parabola is ax2+bx+c=y. In order for you to calculate the minimum of the function you need to find all the three constants a,b, and c. Obviously, to find three unknowns you need a minimum of three equations. Thankfully, you have 3 data points (-2,0); (4,0) and (3,-15). Now using these value you can construct 3 equations. For the first 2 points you simply just put x-value of the intercept instead of x in the formula and y will be equal to 0. For the last one everything is the same, except for y will be equal to -15. After all this is done, you'll have a set of three equations. Take one of them, solve it for a, for example, then put the resulting value for a into the second equation. Now you'd only be dealing with 2 unknowns. Solve this equation for one of the two remaining unknowns and then plot the result into the third equation and then you'll be able to find all three constants. Now that you've got yourself the proper formula for the parabola you can find the minimum in two ways. If you already have done differentials then differentiate the equation for x and equate the resulting equation to 0, since at the minimum/maximum point of a parabola the rate of change of the function is 0. Or else you can just look up the standard formula for the minimum of a parabola. Google will help with that one.

Beans06, the very generalised formula for a parabola is ax2+bx+z=y, right? So, now your available data gives you three data points, so for each of those you can create an own version of the equation, for example for the -2 intercept you'll have: a(-2)2+(-2)b+z=0 Do the same for intersection at 4 and (3, -15) and you'll have a set of 3 equations with 3 unknowns. Now you'll just need to solve those.

I'm not quite sure what your point is. The question was about Earth rotating in the opposite direction, not the Moon. On a side note: depending on the direction of the impact I do believe it's quite possible for the resulting debris to end up on a retrograde orbit. If the OP said that the Earth actually does rotate backwards, then yes, but now we're discussing a pure thought experiment of what would happen if that were the case.

I believe you were referring to Gravitational Frame-Dragging, rather than Gravitational Drag, but either way it's not the effect that causes Moon to drift away. I think the main culprit is the Tidal Acceleration. Coming back to the original question, I believe that all animals that use some sort of navigation, be it Sun, Moon or stars will have a hard time adapting to new conditions. Plants should be fine, though. You can grow plants under artificial lighting with highly variable "day/night" cycles and it doesn't kill them, so reversing the rotation should be fine too.

Which photons are you referring to? First photons that we're capable of detecting? It's about 380000 years after the Big Bang, nowadays known as Cosmic Microwave Background Radiation. I believe that photons, from the moment of their creation always move at c, they can't exist any other way. Wow! And some people say that I like to nit-pick...

Balloons are good, indeed, but what in my thoughts travelling around Titan itself would be just one of the purposes of jet engine. As far as I can see from Wiki page on SSTO, while it is pretty complicated for the example of the Earth, but Titan, having lower gravity, could support creation and use of reusable SSTO spacecraft even with the current technology. For this to work, spacecraft would have to first get up to Titan's stratosphere using aerodynamic lift and atmospheric fuel. Doing this will save a lot of delta-v that would otherwise be wasted on. Obviously, this would be important not in case of a short-term mission, but in the case of colonization. So then I was thinking, that on Earth methane creates an explosive mixture with air at concentrations between 5-15%, but that is with normal atmospheric air containing 21% of oxygen. If we use pure oxygen as oxidizer then even lower concentrations would be combustible, so it might even be possible to use it in Titan's stratosphere, which has just about 1.5% methane. How does that sound?

OK, that makes much more sense now. Viewing free will as probabilistic definitely helps.

Nicholas, I like your solution, but why do you think that water has cooled down to 0oC? What if the ice cube is just 10g? Or 5g? I think as a general idea, studiot's answer is better, to me at least. If the water was in equilibrium with it's surroundings, it will end up at that same equilibrium in the end.