Search found 642 matches

by sevenperforce
Mon Apr 10, 2017 2:36 pm UTC
Forum: Science
Topic: Does the geographical distribution of the northern and southern hemispheres affect the rotation of the Earth?
Replies: 8
Views: 1719

Re: Does the geographical distribution of the northern and southern hemispheres affect the rotation of the Earth?

Is the biggest effect to do with moving closer/further from the poles, thereby moving mass closer/further from the axis, and changing the moment of inertia? That's one of the effects, yes. Another effect is that the distribution of the continental plates changes tidal interactions between the moon ...
by sevenperforce
Mon Apr 10, 2017 1:14 pm UTC
Forum: Science
Topic: Why haven't any animals evolved wheels?
Replies: 22
Views: 3664

Re: Why haven't any animals evolved wheels?

As has been pointed out, this discussion begs the question of whether wheels would actually be useful. It also demands the question of how they would be used. Rather than a wheel per se; I could see the possibility of some creature developing a spherical keratin nodule embedded inside a socket. No a...
by sevenperforce
Mon Apr 10, 2017 1:06 pm UTC
Forum: What If?
Topic: What-If 0155: "Toaster vs. Freezer"
Replies: 43
Views: 8433

Re: What-If 0155: "Toaster vs. Freezer"

Clearly, the real challenge implicit in all of this:

Build a freezer capable of preventing a toaster from toasting bread.

Assuming a 1000-watt toaster, you just need a freezer which draws over 500 watts at the compressor and uses a forced-air fan to circulate.
by sevenperforce
Mon Apr 10, 2017 1:00 pm UTC
Forum: Science
Topic: Does the geographical distribution of the northern and southern hemispheres affect the rotation of the Earth?
Replies: 8
Views: 1719

Re: Does the geographical distribution of the northern and southern hemispheres affect the rotation of the Earth?

The distribution of the continental plates absolutely affects the rotation, tilt, and precession of the Earth. However, the distribution of people and buildings on the earth does not. See What-If #8 . Moving all the people on Earth to a single location and making them all jump at once would only cha...
by sevenperforce
Wed Dec 14, 2016 2:31 pm UTC
Forum: Science
Topic: What to Do With a Nearby Black Hole
Replies: 11
Views: 3018

Re: What to Do With a Nearby Black Hole

I don't recall whether the focal-line terminus of a massive object depends only on mass or on mass and radius combined. If the latter, a nearby planet-sized black hole would basically give us a ready-made lensing telescope more powerful than anything we could build for the next thousand years.
by sevenperforce
Wed Dec 14, 2016 1:23 pm UTC
Forum: Science
Topic: Creationism documentary AMA
Replies: 2
Views: 1972

Re: Creationism documentary AMA

AMA is scheduled from 1 PM to 2 PM. Hope to see some of you there! Can't make it. I'll be at work ... or getting ready for work, if you mean Vietnamese time ... or actually I can make it but shouldn't because I might get too p____d off to sleep, if you mean Pacific time ... or I'll already be in be...
by sevenperforce
Tue Dec 13, 2016 9:50 pm UTC
Forum: Science
Topic: Creationism documentary AMA
Replies: 2
Views: 1972

Creationism documentary AMA

Hey all! 137Films is a Chicago-based film company that makes films about science and science education, and they've just recently announced We Believe In Dinosaurs , a film about the religious creationist organization that has built a life-size replica of the mythical Noah's Ark in northern Kentucky...
by sevenperforce
Fri Jul 22, 2016 2:06 pm UTC
Forum: Science
Topic: Chemistry question: equation products given reagents
Replies: 3
Views: 1447

Re: Chemistry question: equation products given reagents

I can balance equations but only if I already know both sides. Trying to find the following products: It's been a while since I have done chemistry at such exam/test-level, but I presume you're expected that in... Na2S2O5 + O2 = ? ...you're supposed to assume full combustion. Thus (correcting some ...
by sevenperforce
Fri Jul 22, 2016 1:20 pm UTC
Forum: Science
Topic: Chemistry question: equation products given reagents
Replies: 3
Views: 1447

Chemistry question: equation products given reagents

I can balance equations but only if I already know both sides. Trying to find the following products:

Na2S2O5 + O2 = ?

Na2S2O5 + KNO3 = ?

Na2S2O5 + KNO3 + Fe2O3 = ?

Na2S2O5 + KNO3 + C12H22O11 = ?

KNO3 + C12H22O11 = ?

KNO3 + C12H22O11 + Fe2O3 = ?

Thanks!
by sevenperforce
Mon Feb 15, 2016 3:57 pm UTC
Forum: Science
Topic: Landing rockets upright is unnecessary?
Replies: 61
Views: 9031

Re: Landing rockets upright is unnecessary?

Neil_Boekend wrote:Unstable flow separation inside a rocket engine sounds like a spectacularly bad situation

Considering that induced/controlled flow separation has been used as a primary means of gimballing...yeah, exceedingly bad. You-will-not-go-to-space-today-or-maybe-ever bad.
by sevenperforce
Mon Feb 15, 2016 2:48 pm UTC
Forum: Science
Topic: Landing rockets upright is unnecessary?
Replies: 61
Views: 9031

Re: Landing rockets upright is unnecessary?

The backpressure does cause the flow to slow down, but it's still going to be moving rather speedily. The more serious problem is that air getting sucked up into the rocket bell can cause unstable flow separation, potentually making the thrust vector fluctuate wildly. As a result, most engine bells ...
by sevenperforce
Mon Feb 15, 2016 6:11 am UTC
Forum: Science
Topic: Landing rockets upright is unnecessary?
Replies: 61
Views: 9031

Re: Landing rockets upright is unnecessary?

Good question. The flow doesn't get sucked back up into the bell because it's already moving at around 8,400 miles per hour. Although a pressure drop can result in a net force ((P1 - P2)*A), rockets operate more efficiently by simple momentum exchange. Ejecting a superheated mixture of water and dia...
by sevenperforce
Sat Feb 13, 2016 1:43 pm UTC
Forum: Science
Topic: Landing rockets upright is unnecessary?
Replies: 61
Views: 9031

Re: Landing rockets upright is unnecessary?

Yeah, as unstable as the Falcon 9 Stage 1 Booster landings look, they aren't too bad; the mass is all down there at the bottom because the tanks are virtually empty. You can't really do that with a manned vehicle, though, because you need to have your crew module near the top of the rocket. Hence t...
by sevenperforce
Fri Feb 12, 2016 7:01 pm UTC
Forum: Science
Topic: Landing rockets upright is unnecessary?
Replies: 61
Views: 9031

Re: Landing rockets upright is unnecessary?

VTOL spaceplane: http://s16.postimg.org/c2izeon39/Double_perspective_view.png It's just over 90 meters long. With an internal tank volume exceeding that of the Space Shuttle's external tank, it can carry a huge amount of fuel. The rounded-body form factor allows the tanks to form structural elements...
by sevenperforce
Fri Feb 12, 2016 4:17 pm UTC
Forum: Science
Topic: LIGO Gravity Waves: Questions and Answers
Replies: 49
Views: 6782

Re: LIGO - don't understand how detection worked

Well, I suppose in a way it does have something to do with the properties of electromagnetic waves. If you had two rulers, you wouldn't be able to tell the difference, because they are stationary. But a laser beam is traveling at the speed of light, just the same as the gravitational wave. And so th...
by sevenperforce
Fri Feb 12, 2016 3:46 pm UTC
Forum: Science
Topic: LIGO Gravity Waves: Questions and Answers
Replies: 49
Views: 6782

Re: LIGO - don't understand how detection worked

The passage of a gravity wave is supposed to change the pathlength of the arms, detected by a change in the relative phase of a laser beam that travels up and down each arm. What I don't get is if the laser is travelling through the same distorted spacetime that the physical arm resides in, how can...
by sevenperforce
Fri Feb 12, 2016 3:23 pm UTC
Forum: Science
Topic: LIGO Gravity Waves: Questions and Answers
Replies: 49
Views: 6782

Re: LIGO Gravity Waves; how did they determine distance

As would be expected, it takes a very, very large change in the sheet's distortion to produce a ripple that is detectable at all. Also directly equivalent to the difference between a static magnetic field (refrigerator magnets don't take batteries) and a dynamic one (iPod speakers do), right? Exact...
by sevenperforce
Fri Feb 12, 2016 2:46 pm UTC
Forum: Science
Topic: LIGO Gravity Waves: Questions and Answers
Replies: 49
Views: 6782

Re: LIGO Gravity Waves; how did they determine distance

All gravity is a curving of spacetime. Gravity waves transmit energy though, whereas the earth doesn't lose any energy when it sends out its GM/r^2 at you. So, if we go with the (outdated?) rubber-sheet analogy, normally, mass just distorts the sheet statically, but gravity waves are moving ripples...
by sevenperforce
Fri Feb 12, 2016 2:14 pm UTC
Forum: Science
Topic: Landing rockets upright is unnecessary?
Replies: 61
Views: 9031

Re: Landing rockets upright is unnecessary?

Back to the OP topic: I get that landing a rocket on its tail is an inherently unstable arrangement. It's just that's virtually the only way to use the ascent engines to slow down. I think that the simplest thing to do to increase stability is to lower the center of mass and widen the landing legs....
by sevenperforce
Fri Feb 12, 2016 2:12 pm UTC
Forum: Science
Topic: LIGO Gravity Waves: Questions and Answers
Replies: 49
Views: 6782

Re: LIGO Gravity Waves; how did they determine distance

LIGO has two different detectors hundreds of miles apart. Each detector received the same signal, but at slightly different times and from slightly different directions, so triangulation could be used to find the origin. I don't know whether they immediately pointed Hubble in that direction to try a...
by sevenperforce
Wed Feb 10, 2016 3:03 pm UTC
Forum: Science
Topic: Is the entire universe a black hole?
Replies: 13
Views: 2894

Re: Is the entire universe a black hole?

No. Actually, wait. If you have fallen into a black hole and have already crossed the event horizon, you will fall faster than everything "above" you, and slower than everything "below" you. So it will seem to you...as if everything is moving away from you. Huh. That actually mak...
by sevenperforce
Wed Feb 10, 2016 3:00 pm UTC
Forum: Science
Topic: Landing rockets upright is unnecessary?
Replies: 61
Views: 9031

Re: Landing rockets upright is unnecessary?

For some reason, people really seem to think that if we can't get scramjets to work, then we definitely won't be able to get air-augmented/ducted rockets to work. This is not correct. Scramjets are the most challenging sort of air-augmented engine imaginable. Back to the OP topic: I get that landing...
by sevenperforce
Wed Feb 10, 2016 2:53 pm UTC
Forum: What If?
Topic: What-If 0145: "Fire From Moonlight"
Replies: 157
Views: 34711

Re: What-If 0145: "Fire From Moonlight"

The moon is a convex surface so it scatters sunlight in all directions rather than focusing it. That's why it can't act as a mirror.
by sevenperforce
Tue Feb 09, 2016 9:56 pm UTC
Forum: Science
Topic: Landing rockets upright is unnecessary?
Replies: 61
Views: 9031

Re: Landing rockets upright is unnecessary?

The problem is that the extra weight of the duct and associated equipment usually cancels out the extra performance advantages. Whether it's worth the weight is an entirely different question. Slapping ducts onto an existing rocket design is not very smart. Building a rocket engine designed from th...
by sevenperforce
Tue Feb 09, 2016 2:28 pm UTC
Forum: Science
Topic: Landing rockets upright is unnecessary?
Replies: 61
Views: 9031

Re: Landing rockets upright is unnecessary?

I think what some people are suggesting is essentially a scramjet/ramjet where the flame-holder is a rocket engine that provides the initial startup thrust to get it up to ramjet operational speeds then throttles back as the ramjet portion starts providing more thrust. Well in that instance it woul...
by sevenperforce
Mon Feb 08, 2016 7:11 pm UTC
Forum: What If?
Topic: What-If 0143: "Europa Water Siphon"
Replies: 52
Views: 13667

Re: What-If 0143: "Europa Water Siphon"

If air pressure was the reason a siphon worked, water would flow uphill. In reality the air pressure is higher at the low point. Fluids flow from a high pressure to a lower pressure. Gravity and cohesion is the reason a siphon works, IMHO. Gravity, yes. Cohesion...no. Gravity is the reason that a s...
by sevenperforce
Mon Feb 08, 2016 5:00 pm UTC
Forum: Science
Topic: Landing rockets upright is unnecessary?
Replies: 61
Views: 9031

Re: Landing rockets upright is unnecessary?

Earth is...interesting. Our combination of atmosphere, mass, and surface gravity makes it just barely possible to get into orbit. Any harder and it would be prohibitively difficult to get to orbit; any easier and reusable SSTOs would be a snap. Oh well; gives us a reason to push engineering to its l...
by sevenperforce
Fri Feb 05, 2016 2:22 pm UTC
Forum: Science
Topic: Toffo Talks about Trains
Replies: 128
Views: 15610

Re: A new relativity paradox

... The electricity? What he said. Energy is mass, so if energy is moving from the overhead electric wire to the train, mass is moving from the overhead electric wire to the train. Not a lot, mind you (mass flux is equal to the power consumption divided by c 2 ), but some. However, the train is mov...
by sevenperforce
Wed Feb 03, 2016 6:33 pm UTC
Forum: What If?
Topic: What-If 0144: "Saliva Pool"
Replies: 18
Views: 6819

Re: What-If 0144: "Saliva Pool"

I was hoping he'd go through a "if we relax the 'single person' requirement, then what logistics are we looking at?" bit.
by sevenperforce
Wed Feb 03, 2016 3:54 pm UTC
Forum: What If?
Topic: What-If 0141: "Sunbeam"
Replies: 81
Views: 20494

Re: What-If 0141: "Sunbeam"

Yes, that would be ridiculous. With the additional factor of 2 you mentioned before, that's 30 K per hour. Everyone will need to turn on the air conditioning at full-blast. Of course that won't be possible, because everyone will already be burnt to a crisp in the firestorm that engulfs the entire su...
by sevenperforce
Wed Feb 03, 2016 2:20 pm UTC
Forum: What If?
Topic: What-If 0141: "Sunbeam"
Replies: 81
Views: 20494

Re: What-If 0141: "Sunbeam"

Well, I am just an idiot with a keyboard, some educated guesses and a love for these kind of things, while there are plenty of real world astrophysicists around here, but here is my best guess: Of course the beam is not simple, it'll be strongest in the middle and taper of to the ends. Since I can'...
by sevenperforce
Tue Feb 02, 2016 2:53 pm UTC
Forum: Science
Topic: Atomic Science books suggestion? For Layman and scientists
Replies: 11
Views: 2467

Re: Atomic Science books suggestion? For Layman and scientis

Clearly, we need more dangerous nuclear reactors.
by sevenperforce
Mon Feb 01, 2016 2:06 pm UTC
Forum: What If?
Topic: What-If 0143: "Europa Water Siphon"
Replies: 52
Views: 13667

Re: What-If 0143: "Europa Water Siphon"

By adding "rather than through atmospheric pressure" I am summarizing their argument in the introduction. As they explain, there are two competing theories for how siphon works (gravity + liquid cohesion, or gravity + atmospheric pressure), and the question has been controversial even rec...
by sevenperforce
Thu Jan 28, 2016 9:21 pm UTC
Forum: Science
Topic: Landing rockets upright is unnecessary?
Replies: 61
Views: 9031

Re: Landing rockets upright is unnecessary?

I'd anticipate two problems with my channel idea...first, reaction control is going to be limited to how fast the pressure differential can travel down the tube, and second, that the differential burn will change the shape of the "nozzle". Both are bad. I asked this question over on the Sp...
by sevenperforce
Thu Jan 28, 2016 2:16 pm UTC
Forum: What If?
Topic: What-If 0143: "Europa Water Siphon"
Replies: 52
Views: 13667

Re: What-If 0143: "Europa Water Siphon"

Lowering pressure in order to increase the vapor pressure of a liquid and cause transfer across a barrier is not the same as siphoning. Capillary action is not the same as siphoning. If the gravitational potential difference between Europa and Earth was capable of causing water to flow through a cyl...
by sevenperforce
Wed Jan 27, 2016 4:10 pm UTC
Forum: Science
Topic: Landing rockets upright is unnecessary?
Replies: 61
Views: 9031

Re: Landing rockets upright is unnecessary?

That's...dizzingly detailed. But quite interesting. I supposed you'd have to coat the exterior with some very healthy combustion inhibitor, because you really don't want to somehow ignite the thing from the outside during flight. That would be bad, and you would not go to space today. The most promi...
by sevenperforce
Wed Jan 27, 2016 1:44 pm UTC
Forum: What If?
Topic: What-If 0143: "Europa Water Siphon"
Replies: 52
Views: 13667

Re: What-If 0143: "Europa Water Siphon"

There are certainly ways to transport water more than 34 feet upward. Siphoning just isn't one of them. But the problem has trees solved is directly applicable to siphoning. If we just do like the trees, then they are living proof that you can siphon water over a 100 meter tall top point. It is jus...
by sevenperforce
Tue Jan 26, 2016 10:01 pm UTC
Forum: Science
Topic: Landing rockets upright is unnecessary?
Replies: 61
Views: 9031

Re: Landing rockets upright is unnecessary?

Yeah, there would definitely have to be some advances in materials science for this sort of a design to be realized. An integrated engine is a blessing and a curse in a lot of ways. With a lot more area exposed to high temperatures, you're dealing with a significant weight penalty at the outset, but...
by sevenperforce
Tue Jan 26, 2016 6:36 pm UTC
Forum: Science
Topic: Probable ninth planet?
Replies: 30
Views: 4258

Re: Probable ninth planet?

I don't think so. This article mentions very different predictions for size, a little closer and a lot smaller. (And on a wildly inclined orbital plane.) Oh well. I still want to see someone set up a way for people at home to flip through wide field sky surveys along the predicted orbital path to l...
by sevenperforce
Mon Jan 25, 2016 9:35 pm UTC
Forum: Science
Topic: Landing rockets upright is unnecessary?
Replies: 61
Views: 9031

Re: Landing rockets upright is unnecessary?

thoughtfully wrote:I like digging up old threads. I'm sure seven won't mind.

Guilty as charged.

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