For Questions That Don't Merit Their Own Thread

[Spacescifi]

43 minutes ago, JoeSchmuckatelli said:

its a lot more complicated.  Much easier for the side with the tech advantage btw; if you can get a lock outside his detection range and fire... he won't know he's dead and can't take evasive action.

 

But - Missile lock isn't everything - it simply says that the targeting computer of the missile has a solution and you're free to fire the weapon, and thus rely upon its programming and abilities to take out the target.  Yet for the target aircraft, there are countermeasures and evasive maneuvers and just dumb luck that come into play.  Note - the pilot actually has to make the decision to fire.  In the case you cited, the pilot may have been too busy flying the plane to realize he could fire.  This is where training comes in.

 

So if you have both a technological and a training advantage - odds are in your favor.

 

 

Well...if the MIG fired the missile off what are the odds it would hit the American jet diving for the desert?

My guess? The US pilot was trying to confuse the missile...probably thought it was heatseeking and would see one HUGE target as the jet neared the ground instead of homing in on the jet like it should.

There is no debating the tech and training advantage though.

US pilot even said he felt sorry for the guy...but still enjoys staying alive 

[Spacescifi]

17 hours ago, DunaManiac said:

I know that gravity also slows down time, in fact you could sit in orbit around a black hole and time would slow down, but the specific question is that if time slows down when things move, how fast would it need to go before it would become noticeable.

 

Answered and fixed:

https://en.m.wikipedia.org/wiki/Time_dilation

 

Edited November 21, 2020 by Spacescifi

[JoeSchmuckatelli]

@Spacescifi. Thanks for the edit 

@DunaManiac there are guys who understand the numbers and can explain using the formula.  I'm not one - but the answer seems to be that time dilation is a constant effect of motion.  So to your point 'how fast before you notice it' - I think Heinlein describes this in Time for the Stars: you need to travel really fast for a long time (which then becomes 'relative' as to how you define 'a long time') 

Edited November 21, 2020 by JoeSchmuckatelli
Problem resolved

[AHHans]

12 hours ago, Spacescifi said:

Answered?

Open main menu

Please just copy & paste the link to the site like so: Time dilation

In addition to that being *bleep*ing annoying there may also be copyright issues.

[kerbiloid]

I would expect an original-size image file with screenshot of the whole wiki article.

Or a video of its scrolling.

Edited November 21, 2020 by kerbiloid

[DDE]

18 hours ago, DunaManiac said:

How fast does something need to go before time slows down noticeably? I know that all objects experience time slowing down when moving, but how fast until it reaches a substantial amount, like a couple hours or minutes?

Lemme fetch some tables from @nyrath...

http://www.projectrho.com/public_html/rocket/slowerlight3.php#gamma

[JoeSchmuckatelli]

On 11/20/2020 at 11:34 AM, JoeSchmuckatelli said:

Is it fair to assume Mercury is a planet?  It does not look to have enough 'oomph' to clear its own orbit... 

 

Edit: also, how wide would the 'habitable zone' be around the largest star - and at that range, could it actually have a planet in orbit?

These are actually real questions  and I'm interested in mecury - despite the controversy over Pluto.  

 

And again - are the largest stars capable of a planet being in a stable orbit within the habitable zone

Edited November 21, 2020 by JoeSchmuckatelli

[DDE]

19 hours ago, Spacescifi said:

It probably pays to keep your plane's nose facing the target because your missile will run out of propellant faster than they do in videogames.

What do you know on this?

If you are locked on to by another jet with a missile and they fire, can you actually evade it?

Maybe it depends on missile type?

A lot depends on the particulars, but jet engines and wings are your advantages. A missile can maneuver very violently on paper, but it actually has limited momentum and the solid motors (even air-augmented ones) don't last too long. So a combination of running and outturning it are all possible:

Conversely, there are guaranteed kill zones where no dodging can help. The result looks somewhat like this:

[K^2]

On 11/21/2020 at 11:13 AM, JoeSchmuckatelli said:

And again - are the largest stars capable of a planet being in a stable orbit within the habitable zone

Yes, with caveats. The orbit would be stable, the habitable zone wouldn't be. Giant stars evolve rapidly, and habitability of a particular region can change over hundreds of thousands to tends of millions of years, which is nowhere near enough to establish a stable biosphere. Main sequence stars, like our Sun, evolve over billions of years, in contrast. In addition, blue giants will generate way too much radiation for planet to truly be habitable, despite the fact that it's in habitable zone, and red giants are going to be ejecting a lot of matter, blowing away atmosphere of any terrestrial planet in habitable zone. A planet might be briefly genuinely habitable during a yellow giant phase of a massive star.

In short, stable orbit in habitable zone yes, but actually habitable - unlikely, and certainly not capable of life evolving on such a planet, based on everything we know.

 

Edit: Actual extents of habitable zone will depend on spectral type. Habitable zone.

Edited November 23, 2020 by K^2

[JoeSchmuckatelli]

Which makes a better supercomputer - systems build around CPUs or GPUs?

 

 

[magnemoe]

12 minutes ago, JoeSchmuckatelli said:

Which makes a better supercomputer - systems build around CPUs or GPUs?

 

 

Depend on your task, for stuff like rendering GPU is much better obvious
However if you need to run plenty of branching and loops and this is not equal for your treads the cpu wins 

In short the GPU is much better at doing the same stuff many times at once, CPU is much better at doing lots of different things at once.
Now then making software you want to split things up so each to its part. 
 

[JoeSchmuckatelli]

Let me refine this - what about for applications like cracking codes or encryption - would the cpu or gpu have an advantage? 

[Terwin]

45 minutes ago, JoeSchmuckatelli said:

Let me refine this - what about for applications like cracking codes or encryption - would the cpu or gpu have an advantage? 

The really depends on what you are doing.

If you are trying to create a rainbow table(a long list of pre-and post encryption passwords that you can then use to look up encrypted passwords to know the unencrypted values), you would obviously want to use a GPU as you are calculating the encrypted value for thousands of potential passwords and that can be done in parallel.

Other activities may work better on a CPU, it all depends on what you are trying to do. (example: a rotating cypher like Enigma, where the encryption state changes for each character)

In short, GPU is good for performing the same task in parallel, CPU is better for performing more convoluted or distinct tasks, just as magnemoe said.

Note: 'cracking codes or encryption' covers a very broad range of activities, you would need to be much more specific to get a specific answer.

Edited November 25, 2020 by Terwin

[JoeSchmuckatelli]

Thanks fellers. 

Every day I learn a little more about just how much I don't know 

[ARS]

When a tensile test is performed on a metal sample, after the sample breaks, there's a noticeable heat on the sample, with harder metal typically giving off more heat than softer ones. My question is, does this heat actually come from the kinetic energy of pulling the sample apart (and converted into heat before the sample finally breaks)? Does the amount of total heat on the sample equal with the total energy required to break that sample?

[K^2]

1 hour ago, ARS said:

Does the amount of total heat on the sample equal with the total energy required to break that sample?

There is actually a lot going on.

Lets limit this to something simple, like pulling on a wire until it snaps. First, material matters. Some polymers, rubber bands in particular, will work exactly opposite of what I'm going to describe in terms of heat during portions of the process. So again, lets simplify, and consider just a simple case of a metal wire. As you start pulling on the wire, and the wire extends, you are putting in work. Most of that work goes into deformation of the wire. But even under perfect conditions, temperature of the wire will change. First question you should be asking is whether wire gets colder or hotter. Formally, you need to work out how the change in stress affects the free energy in the wire, which will determine how the temperature changes... There's a shortcut in form of Le Chatelier's principle. If you heat up the wire, it will relax and extend. That means pulling on the wire will make the wire cool down a little bit. (The rubber band would warm up, instead, which means you expect that heating up a rubber band would make it contract, rather than relax, which, indeed is what happens. Rubber bands are weird. Thermodynamics is weird.)

At some point, wire will reach limit of elastic deformation and begin to yield. At this point, additional work you put in no longer increases the stress in the structure by nearly the same amount, and since energy can't be going anywhere else, you must be generating heat. I don't know if anybody ever tried to use change in temperature to measure yield strength of a metal wire, but that should work in theory. Plotting stress/strain is still easier, though.

As the wire keeps extending, you will pass ultimate strength, and eventually cause wire to snap. When the material is fractured, some amount of energy will go into making a new interface. The energy here is comparable to evaporating a few atomic layers of material. In other words, in most practical cases, and unless you have very complex shape of the fracture, very little energy goes into that. However, nearly all of the energy stored in tension of the wire is released at this point. It has to go somewhere. That somewhere is (mostly) heat.

So, putting it all together. Some of the energy put into stressing the wire does, indeed, go to the fracture, but it's a very small amount. Most of the work done against the wire when you stress it becomes heat. Some of that heat is generated before the fracture and some after. Which one is greater will depend on material. Looking at stress/strain curves for some metals, it looks like more work is done during inelastic deformation than during elastic deformation, so I suspect most heat will be generated prior to the fracture.

There are materials that will behave in far more interesting ways, and there are other ways you can apply stress to material, which will all work a little different. But this example should give you some idea. And unless chemical or phase changes are involved, I don't think you'll find cases where the heat in the end came from something other than the work you did deforming material, whether the energy became heat before or after the fracture.

[JoeSchmuckatelli]

@K^2 - so when I bend a coat hanger wire back and forth rapidly to break it, I notice that it heats up - just like stretching a rubber band several times in a row, and I always thought that working something like that generated heat.  Interesting to read that they're different.

 

So back to the wire... I'm guessing the bending is exerting different forces than the stretch you described, and that's why I notice the heat? 

[K^2]

2 hours ago, JoeSchmuckatelli said:

So back to the wire... I'm guessing the bending is exerting different forces than the stretch you described, and that's why I notice the heat? 

No, it's about going past elastic limits. Bending or stretching enough to cause permanent deformation will generate heat in both cases.

For rubber band, think of it as cylinder with gas. If you go back and forward a bunch of times, it gets hotter on average, but any given stroke can increase or decrease temperature, depending on direction. That's why yoy can build refrigerator out of rubber bands, just like you can with compressed air.

Simple experiment. Take a rubber band and stretch it. Hold stretched for a bit to let it reach room temerature, then let the band relax and touch it to your lips. You should feel that it's cooler than before.

[JoeSchmuckatelli]

On 11/26/2020 at 4:55 PM, K^2 said:

No, it's about going past elastic limits. Bending or stretching enough to cause permanent deformation will generate heat in both cases.

For rubber band, think of it as cylinder with gas. If you go back and forward a bunch of times, it gets hotter on average, but any given stroke can increase or decrease temperature, depending on direction. That's why yoy can build refrigerator out of rubber bands, just like you can with compressed air.

Simple experiment. Take a rubber band and stretch it. Hold stretched for a bit to let it reach room temerature, then let the band relax and touch it to your lips. You should feel that it's cooler than before.

I will try this.  And then show my kids!

 

Okay - next question:  Is Jupiter responsible for the solar system having an orbital plane?

 

I know that there is some expectation that everything accreted from a spinning disk of SN remnants... but it seems to me that the gravity from a planet as large as Jupiter might also assist in getting other planets' orbits to align.  i.e. whenever one is above or below Jupiter's orbital plane, its gravitational force is at an angle from the plane of the other planet; and all things being equal should exert some sort of normalizing on the other smaller planets

 

Edited November 29, 2020 by JoeSchmuckatelli

[ARS]

10 hours ago, JoeSchmuckatelli said:

Is Jupiter responsible for the solar system having an orbital plane?

The answer is … no, and I don't think it worked that way...

Let me explain. You see, Most major planets in our solar system stay within 3 degrees of the ecliptic. Mercury is the exception; its orbit is inclined to the ecliptic by 7 degrees. The dwarf planet Pluto is a widely known exception to this rule. Its orbit is inclined to the ecliptic by more than 17 degrees. It makes sense that most large planets in our solar system stay near the ecliptic plane. Our solar system is believed to be about 4 1/2 billion years old. It’s thought to have arisen from an amorphous cloud of gas and dust in space. The original cloud was spinning, and this spin caused it to flatten out into a disk shape. The sun and planets are believed to have formed out of this disk, which is why, today, the planets still orbit in a single plane around our sun

Since Jupiter is already at the current ecliptic plane, it makes sense that any planets in the early age of solar system that's not at the ecliptic plane would be either thrown out or forced into the current ecliptic plane. However, this is extremely unlikely as most of the planets are formed near-simultaneously on the ecliptic plane, their largest deviation of inclination from the ecliptic plane should be few degrees at best. This doesn't really apply on the planets that sits on the outer edge of the solar system though. Pluto for example has 17 degrees of deviation in inclination. At that distance, Jupiter's gravity is too weak to influence Pluto's orbital plane. As you peer further into deep space, many Trans-Neptunian objects in deep space have extreme deviation from solar ecliptic plane. Some of these are legitimately formed at the same time as the solar system, but most of them are captured kuiper belt or oort cloud object

In any case, it seems that the main driving point of the orientation of the ecliptic plane is the star at the center of the system itself. The massive gravity well it emits defines the plane itself in the first plane when the system are born. This massive gravity field also affects the angle of the entire system's ecliptic plane relative to the galactic core, depending on the star's rotation and inclination as it formed. But what about double star system? Surprisingly, it affects the ecliptic plane too! With a young double star system – surrounded by a planet-forming disk – whose disk lies at right angles to the orbits of the two central stars. In other words, the two stars do orbit more or less in the plane of each other’s equators. But their star-forming disk has flipped up over the orbital plane of those stars. It’s oriented instead above the stars’ poles

This, of course raises an even bigger question: What the ecliptic plane of the trinary star system looks like?

[K^2]

6 hours ago, ARS said:

The original cloud was spinning, and this spin caused it to flatten out into a disk shape.

This isn't exactly wrong, just not a great way of saying it, IMO. It makes it sound like the disk got stretched out by centrifugal forces or something like that. But it's more about things averaging out due to interactions and collisions. You start out with everything orbiting at arbitrary inclinations and that results in a lot of near misses or direct collisions. Because interactions aren't generally elastic, the difference in orbital energies and angular momentum is decreased by every interaction. Most of the matter ends up with zero angular momentum and becomes part of the sun. But because, statistically, there's going to be a predominant spin, the average isn't exactly zero. So whatever matter ends up left orbiting the star is going to have the same orientation of angular momentum, id est, form a disk.

So yeah, the disk is there because of the spin, but it's more that things remained as part of the disk because of the spin, rather than original shape getting flattened into the disk because of it. The flattening itself still happens primarily due to collisions.

[ARS]

Is it correct when I said "Cold is the state of non-energy, the opposite of hot where there's a lot of energy"?

[kerbiloid]

No, the body still has energy except the kinetic energy of its particle oscillations, and quantum effects still can cause motions or changes.

***

Jupiter = 318 Earth masses.
Saturn = 95 Earth masses.
Other trash = ~40 Earth masses.

Jupiter orbital plane IS the solar system orbital plane. Others are just a random error.

[K^2]

3 hours ago, ARS said:

Is it correct when I said "Cold is the state of non-energy, the opposite of hot where there's a lot of energy"?

Temperature isn't related to energy, but rather changes in energy. Consequently, just knowing that object A has more energy than object B doesn't tell you anything about their relative temperatures.

Temperature is a bit of an abstract quantity in physics. The fact that it's measurable is almost absurd. Fundamentally, the idea of temperature comes from the fact that if you bring two objects in contact, one of them might start taking energy from the other, and that will continue until some sort of equilibrium is achieved. We say that the object that gives up energy is hotter than the object that receives energy. And that's sort of it. This might sound extremely underwhelming, and it would be entirely so, except that there are two more observations you can make.

First, this relationship is well ordered. If A is hotter than B and B is hotter than C then A is always hotter than C. If you just think about objects exchanging heat through random interaction at whatever interface, this isn't an obvious quality at all. But it holds, and is absolutely crucial for all of thermodynamics to work.

The second is that energy that is being exchanged, which we call heat energy, is related to the measure of disorder in the system, which is entropy. I'm skipping centuries of physicists literally going insane, but what it really comes down to is that the change in heat energy is proportional to the change in entropy, and the proportionality constant is monotonic with the above relation ordering of temperatures. That is, without loss of generality, we can say that this proportionality constant is the temperature, write down dQ = T * dS, and this T is the thing we're measuring when we measure temperature.

Which should immediately lead you to asking how the *bleep* a thermometer measures THAT? And that's a bit of a lengthy lecture and just small part of the reason why thermodynamics and statistical mechanics are the most underappreciated fields of physics. Add to that the fact that we learned how to measure temperature long before we learned to measure atmospheric pressure, despite the later being such an obvious concept in comparison, and that the relationship between heat and entropy was derived back when people thought that heat was a kind of invisible fluid, and the question pile up a lot faster than they can be answered.

Unfortunately, the math requirement to properly appreciate thermodynamics is at least at partial differential equations level, but if that doesn't scare you away, and especially if you're still in school learning that stuff, I do encourage you to pursue it. It's just way more than can be covered in a forum reply or even an entire thread.

[ARS]

4 hours ago, K^2 said:

Temperature isn't related to energy, but rather.......

Thanks for the answer. It really helps me to define the changes of energy between cold and hot temperature.  I got the idea for the question when I stumbled upon a sentence:

"...coldness isn't energy, but rather lack of it (from the point of view of our environment's parameters)..."