# Janus

Resident Experts

2037

26

1. ## Gravity

Magnetic fields have polarity. You have a North and South pole. Like poles repel each other and unlike poles attract. The poles always occur in pairs (a magnet will always have both North and South poles) Because of this, it is possible to arrange the poles in such a way that all the poles cancel each other out and you get no net attraction or repulsion. Gravitational fields have no polarity. They are purely attractive; mass attracts mass. The more mass, the greater the attraction. There is no way to arrange things to get a repulsion or cancellation. But, compared to magnetic fields, gravity is very weak, and it take a considerable amount of mass for this attraction to be easily measured. But, as swansont has already noted, we have measured gravitational attraction between relatively small masses. The earliest such measurement was done by Henry Cavendish in 1797. He took two brass* spheres which were placed on the ends of a long rod which, in turn, was hung from a piano wire at its midpoint. Two more larger Brass spheres were placed near the suspended spheres so that any attraction between them would rotate the rod and twist the piano wire. Then, by measuring how much rod rotated, and knowing how much torque it would take to twist the wire by that amount, he could work out just how much force was attracting the spheres to each other. And since he also knew the mass of the spheres, he was able to derive the constant of proportionality for gravity. This, in turn allowed him to work out the mass of the Earth. Up until then, while we could measure how much gravitational force there was between the Earth and an object of a known mass, and we knew how far the object was from the center of the Earth, we were still left with two unknowns: the mass of the Earth, and the gravitational constant of proportionality. Knowing either one would allow us to work out the other. Cavendish's experiment gave us the value of the gravitational constant, which meant he could now calculate the Earth's mass. Because of this, Cavendish has been referred to as "The man who weighed the Earth". *he used brass as it had no magnetic properties that could have skewed the results.
2. ## Atomic Physics and thougts about gravity effecting time

When we say that gravity has an effect on time, it is important to understand, that is a difference in gravitational potential that is important and not any difference in local gravity strength. A clock at the top a mountain runs faster than one at sea level because it is higher in the gravity well of the Earth, not because gravity is a bit weaker there. If fact, if gravity didn't decrease with altitude, and remained the same at the mountain top as at sea level, not only would the mountain clock still run faster, but the difference between its tick rate and the sea level clock would be even larger. This is despite the fact that both clocks would experience exactly the same magnitude of gravity.
3. ## Question that bothers me for a really long time....

I'm going to focus on this, Others have already explained that you would see the both the Moon and smaller Sun as they were ~8 min prior to the moment you see them. But, just because you "see" them that way, doesn't mean they are in a "different time-frame" from you. So, for example, if the Moon has large clock face on it, and you, from your position, see it reading 11:52, while your clock reads 12:00, you can't conclude that is is 11.52 on the Moon when your clock reads 12:00. The Moon clock ticked off 8 min in the time the light reflected off it left. So, When you see it read 11:52, it actually reads 12:00 just like your own clock. The reason I bring this up is that you mentioned Relativity, and many people get confused about this. They think time dilation etc, is all just related to what we visually see. This is not however the case. In Relativity, we factor out any time difference caused by the time it took the light to travel the intervening distance, and are only concerned with what is left over after that. With your Moon example, we, for the sake of making it simple, assume that the Moon is not moving relative to you, and are ignoring any effects caused by gravity. In this case, there is no net time difference between you and the Moon ( even though the image you see of the Moon is ~8 min delayed)
4. ## Is window 11 is safe to use?

I've seen a few YouTube videos discussing its release. It seems that the PC requirements for installing it are quite stringent. Only pretty recent CPUs are compatible. (Microsoft has release an "approved CPU" list). MS had also put out a "Health Checker" do you could see if your PC was up to the task, But the backlash from it telling so many people that their PC couldn't run Windows 11 caused them to pull it. Out of curiosity, I checked my CPU against the approved list, and it was on it (my PC is less than a year old), But like @StringJunky, I'll think I'll wait and see.
5. ## Would lining the moon with reflective surfaces turn it into a de facto convex mirror?

This is what the Moon as a mirror would look like viewed from the Earth with a telescope. That small bluish dot in the center is the Earth's reflection.
6. ## Alien origin thought experiment.

Hal Clement wrote a short story dealing with telepathic aliens communicating with Human. The basic outline was a spaceship containing renegades from their own race, has to do a forced landing on Earth. They are a telepathic race. They land in a remote place where they contact a single human, and they spend a good time learning how to read and interact with his mind. (The idea being that once they learn to do this they can use it to control all humans. And their plans were not good. Once they succeed with this one person, they try and implement their plan, only to have it fail. The problem was, that Humans, not being a naturally telepathic race, had thought patterns that varied from individual to individual. The mental link they had formed with the one human didn't translate into forming it with any others.
7. ## If a person touch an iron pole, and a TASER gun hits him/her.......

Since a TASER doesn't use the Earth ground as part of its circuit, touching a metal pole while being hit by one will make no difference. If the TASER hits the pole: For one thing, the darts won't stick and would glance off, and even if they stuck, the circuit would be completed through the pole and not the person touching it, so they would not be effected by it.
8. ## Interesting space facts

Your last fact is open to what definition of "day" you use. You are using the sidereal day or the rotation relative to the stars. However, the usual use of "day" refers to the Solar day which is the time it takes for the Sun to go from noon to noon. Since Venus' rotation is retrograde (its rotates in the opposite direction to that it orbits the Sun, it's Solar day is only 116 day, 18 hours long.

10. ## Time for a different view (hypothesis)

The disparity between the clocks at any given moment fully depends on the the Frame of reference from which it is being measured. There is no "universal, actual" disparity. The importance of bringing the clocks back together is that this produces a situation where all reference frames agree on the exact amount of disparity between the clocks. In other words, all frames agree that the clocks read the same when initially separated, and all frames agree on the difference between the clocks when reunited, but they will not all agree as to how the difference between the clocks accumulated during the period between those two events.
11. ## The Greatest Laser Experiment In History - FECORE

I just recently saw a video where someone examined an "experiment" done by FE proponents, Dealing with looking across a large body of water at a building. They worked out how much of the building "should" be hidden by the curve, and then pointed out that more of the building was seen than predicted by there being curvature. The examiner pointed out two things: 1. They failed to take into account refraction( as mentioned in earlier posts). 2. The ground floor of the building was not itself at water level, but several yards above it. Once these were taken into account, the amount of building they saw matched the predicted curvature. But the other more interesting thing he pointed out was that, In their own video, some of the building was hidden below the horizon. With a flat Earth, all the building should have been visible. They never even address this and sweep it under the rug. This is typical of the type of intellectual dishonesty they indulge in. Some of the other stuff I've seen makes me me wonder if they just competing to be the poster child for the Dunning-Kruger effect.
12. ## Speed of light (hijack from Time for a different view (hypothesis))

By what experiment? Keep in mind that this statement refers to the speed of light in a vacuum ( and not while traveling in a medium), and measured locally ( not its coordinate speed)
13. ## Hijack from What If the Earth needed Global Warming in its Atmosphere.

Sorry, that makes no sense. In a chemical explosion, the energy comes from the rearrangement of the molecular bonds. The difference in bond energies between the starting and resulting compounds is expressed as an increase of kinetic energy of the resulting compounds. These bonds involve the outer electrons of the atoms E=mc^2 would only come in if you were to very carefully measure the mass of the bomb before detonating, and were able to contain all of the resulting bomb material, let it cool back to the initial bomb's temp and then measure it ( and only it). Then you would notice a very, very slight decrease in mass. For acetylene, the difference works out to be in the range of 1 x 10^10 grams per gram you started with. E= mc^2 tells you how much energy you can get if all of m is converted to energy. But with chemical explosions, m( the mass converted to energy) is minuscule compared to M, (the total mass of the explosive) It is so small, that it is, for all practical purposes, immeasurable. You need a nuclear reaction, dealing with the bonds holding the nucleus itself together to get measurable changes between before and after masses.
14. ## Hijack from What If the Earth needed Global Warming in its Atmosphere.

Antimony density as a solid: 6.697 g/cm^3. As a liquid: 6.53 g/cm^3. Another way of expressing this is that 1g would have a volume of 0.15314 cc as a liquid, and 0.149320 cc as a solid. Since the mass would remain the same while going from liquid to solid, it would take up less volume after doing so. Bismuth, as a solid has a density of 9.78g/cm^3 as a solid, and 10.05g/cm^3 as a liquid. It's density goes down going from liquid to solid, and this its volume per unit mass goes up.
15. ## Who coined the phrase "freedom of speech"?

First amendment of the US constitution: Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances. So the "right of Freedom of speech" pertains to the limits the US government has in this manner. It does not matter if the term "freedom of speech" already existed or who first coined it.
16. ## Life Near a Red Dwarf Star

The period over which tidal locking would occur is highly sensitive to the distance between the bodies, and varies by the distance to the power of 6. It is less dependent on the mass of the primary. The relationship ( assuming all else is equal) is T = a^6/M^2 So, if we take a very luminous red dwarf like Lacaille 8760 with a mass of 0.6 that of the Sun, and a Earth equivalent position in the habitable zone of 0.268AU, you get a time period for tidal locking of roughly 1/1000 of the the time it would take for the Earth to tidal lock to the Sun. For a smaller star like Proxima Centauri at 0.12 solar masses and a habitable zone distance of 0.032AU, the tidal locking would take 1/13,000,000 of the time. Red dwarfs also have spend a longer period in their pre-main sequence stage (a billion years or so), Thus a planet would be subject to tidal braking for a long period before even being considered as hospitable. So the odds are pretty high that a planet within the habitable zone of a typical red dwarf would be tidally locked.
17. ## Gravity (split from What is gravity)

That was the argument put forth by Galileo against the Aristotelian model of gravity that posited that heavier objects fell faster than lighter ones. It was not meant an argument against gravity itself, but against that particular model. He wasn't saying that gravity didn't exist, but that it didn't behave like Aristotle said it did. The model for gravity that replaced the old one didn't suffer from this feature.
18. ## Proof – Mars Orbited close to Earth 1350 BC

Of course no mention of the fact that if Mars had been at geostationary orbit distance from the Earth it would have pulled all the Earth's oceans into 6 km high tidal bulges.
19. ## Dogs and/or Cats

Growing up, we had a Siamese cat which had quite a reputation (It once chased a dog several times it size off our property.) Some people got to the point, that when they came over the first thing they would do was look around nervously and ask "Where's the cat"? And we had to warn people that if the cat came around don't reach down to pet her or your likely to pull your hand back bloodied. Now he wasn't that way with anyone in our household. (There were times when the cat would get under Mom's feet in the kitchen and she'd just pick her up with one hand and toss her out, and cat did nothing.) AND, she was not that way around children. Kids could get away with anything, and while she might eventually go off and hide, she never once even hissed at them. It's like she knew that they were young, didn't know any better and deserved leeway.
20. ## Dogs and/or Cats

Right after I retired, I started taking morning walks for the exercise. My wife usually would join me, but a few weeks in she tweaked her back and couldn't, so I took my walks solo for a while. We had a cat at the time. Every day, when I got back from my morning walk, he come running, meowing, jump up onto the back of the sofa (which was near the front door), And wait for me to put my head down so he could give me a head bump. Then he'd jump down and go about his business. He'd already been fed, and my wife always fed him anyway, and It wasn't as if he had been lonely, as she had been home with him all morning, he just wanted to greet me when I came home. Like others here, I've had both dogs and cats as pets over my lifetime, and understand the pluses and minuses of both.
21. ## Today I Learned

My paternal Grandfather was 6 when the Civil war started (Born in Dec of 1854), though he didn't come to the US until 1883.
22. ## Synchronizing clocks in different frames of reference.

You could set things up so that, from a given frame, the clocks started and ended "in sync", but this would require artificially adjusting the tick rate of the clocks. Thus you could get this as measured from the rest frame of the lower row of clocks. All the clocks in both rows remain in sync. However, when you transition to the rest frame of the upper row of clocks, you get this: The only moment when any two clocks read the same is when they are passing each other.
23. ## "Wait a carrot-picking minute...

Just after Thanksgiving, I finally updated my 7+ year old computer to a new "gaming"* computer. This has allowed me to upgrade Blender to the latest build, which has a number of new features and tools, as well as driving the render times down significantly. For example. One of the Star Trek matte paintings I tried to duplicate with Blender was of Stratos, the cloud city. While modeling the buildings wasn't that difficult, the clouds became problematic. In order to get the right look, you had to create a light scattering volume. This means that the render engine has to take into account how light behaves as it passes through the whole volume of the cloud. With my old computer, this meant hrs and hrs of render time, during which time I couldn't use the computer for anything else. I kept putting it off, thinking I would set the render going while we were away from home. Then Covid hit, and we weren't going anywhere. With the new computer, I decided to start the whole project again from scratch. (Mainly because the new version of Blender had a different model for making clouds) This is the result: In contrast to my old system, this render only took a few minutes. * Not that I do much in the way of gaming. It is is just that best the specifications for running Blender (good GPU etc.) tend to match those used for gaming. Though my daughter and her boyfriend did get me the newest Microsoft Flight Sim for Christmas.)
24. ## Friends Walking !

There is a formula for this, it is the same one used to find synodic periods for planets etc. (for example, how long it takes between Earth and Mars passing each other as they orbit the Sun.) The formula is T = 1/(1/p1-1/p2) Where p1 id the time it takes for one plane to complete is orbit and p2 is the time for the other planet to complete is orbit. In this case we are not given times, so we will simply give B a complete circuit walking time of 1 time unit and thus A has a complete circuit walking time of 1/2 time unit. Thus for when they are walking in the same direction T = 1/(1/(1/2)-1/1) - 1/(2-1) =1 Meaning that A passes B every time B has completed a complete circuit. This works out to 5 times if you count the last time they meet up again at the end of the walk (4 if you don't. For when they walk opposite of each other you make one of the times negative, giving T=1/(1/(1/2)-1/(-1)) = 1(2+1) =1/3 A and B meet when B has completed each 1/3 of his complete loop, and since B makes 5 complete loops, they meet 15 times if you count the last meeting ( 14 if not). So Give Jon O'Starr a star.
25. ## Inertia/acceleration question

As swansot has already mentioned, it isn't quite that simple. There will be a gradient. Not only that, but there is the fact that the air in your ship will already be under pressure. If it is at 1 atm, this pressure is the same as caused by the weight of a column of air at constant sea level density which is 8.5 km tall.( at 1 g of gravity). So let's say your spaceship is 10 meters long and full of air at 1 atm. If you were to accelerate at 850 g, that air would be "pushed back" towards the rear of the ship. That 10 m column at 850g would act like a 8.5 km tall column at 1g. The air pressure at the rear of the ship will double. (but not increase by 100's of times.) The pressure would decrease as you moved towards the nose of the craft, but in this scenario would not decrease to zero. And of course, this would only occur during the acceleration phase So, if the ship accelerates up to 10,000 mph, that is the same as 4444 meters/sec. 850g is 8330 m/s/s, so it would take just a bit over 1/2 sec for your ship to go from 0 to 10000 mph at that acceleration. It would be during this time that the air would be compressed towards the back of the ship. Once the ship attains it's target velocity and stops acceleration, it will return to its previous uncompressed state. And while the air would start to compress towards the back the instant the ship begins acceleration, there would be some lag before it could come to its new state, and then some lag before it can return to its previous state once the acceleration ceases.
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