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Janus

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Posts posted by Janus

  1. 18 minutes ago, Gian said:

    MOONTANMAN

    O.1% of the sun's light??? So essentially it's about as light on the surface as a starry night here on Earth. I think Prof John Zarnecki (of Huygens Probe fame) said it would be like a deeply overcast day here on Earth, which given the distance I was surprised at. 

    I think it's probable cloud cover is total on Titan, so future space tourists won't be able to see Saturn hanging in the sky.

    I'll see if I get in touch with one of the Huygens scientists to find out then report back here.

    Cheerz

    GIAN🙂xxx

     

    Direct sunlight ~100,000 lux

    0.1% of that 100 lux, which is equivalent to an heavily overcast day, and brighter than that of the hallway lighting of a typical office building. A moonless clear night is ~0.002 lux

  2. On 3/12/2024 at 1:27 PM, Photon Guy said:

    Ants are extremely strong for their size. Apparently ants can lift over 1000 times their body weight. As such, Im wondering how ants would be on planets with really high gravity, much higher gravity on earth. They would probably do just fine I would think. 

    Ants can do this because of something called the square-cube law.   When you increase the size of something by a given factor you increase its surface area and the area of its cross-section by that factor squared, and it volume (thus its mass) by that factor cubed. The strength of limbs are dependent on the area of their cross-section.  Which, as the size increases increases at a slower rate than the mass/weight of the animal.

    Increase an ant to the size of a man, and it wouldn't even be able to support its own weight. Conversely, shrink a man down to the size of an ant, and they'd put a ant to shame in terms of strength.

    So in terms of higher gravity, this just means that smaller animals would generally fare better.

  3. TIL that I was born on a continental divide.  I was born in the Mesabi range in MN, which I learned is part of the Laurentian continental divide.( a dividing line between which way water flows to the ocean.) It is one of 6 in North America:

    Great, Arctic, St. Lawrence, Laurentian, Eastern, and Great Basin.

    In addition, where I lived was also where the St. Lawrence divide meets up with the Laurentian divide.

  4. 3 hours ago, jajrussel said:

    So there is a distinction there is F=ma     push

    then there is F=GMm/R2      pull

    F =ma seems incomplete as a formula because it only accounts for how m is affected by acceleration, but what it seems to me doesn’t matter, because then, who? I think it is credited to Einstein, says acceleration is the same as gravity. So if F= ma then gravity can not be a force because you have to multiply acceleration which is the same as gravity times mass to get what is called force, so gravity and force can not be the same thing. Is this why it is said that gravity is not a force?

     

    Again, F=ma merely gives a relationship between force, mass, and acceleration.    It does not have anything to do with push or pull.  It gives the magnitude of the force required, and isn't concerned as to the nature of, or how this force is provided.

    Here is another equation : F= mv2/r

    It tells you how much force is needed to constrain a mass to moving in a circle with a radius of r if it has a mass of m and has a speed of v. It makes no difference as to how that force is applied.  It can be by a rope anchored at the center of the circle, a rocket engine mounted on the mass applying inward thrust, by the gravity of a central mass, or by the friction between a car's tires and the road.

  5. 1 hour ago, jajrussel said:

    Okay, I was thinking for the first question that if both ma and GMm/Requaled force I could write it F=ma=GMm/R. Which is not exactly how I wrote it the first time but I borrowed the shorthand from swansont for the latter portion. What I thought I was writing is force equals mass time acceleration ,and force equals G times mass one times mass two divided by the radius squared. Since force is described as equal to both expressions. I assumed it would be okay to write F=ma=Gmm/R since the expression on each side of the equal signs I presumed to be equal. 
    As for the second question.

    Are you saying that by canceling mass out, force and acceleration are shown to be the same?

    It is really important to grasp what the variables mean in each equation.

    In F=ma,  we are talking about the amount of force needed to give a mass of m an acceleration of a

    With F = GMm/d^2 we are talking about the gravitational force acting between masses M and m at a center to center distance of d.  To make this clearer, F is often written as Fg

    Now if we were considering how much acceleration mass m would undergo as the result of gravitational attraction between m and M, Then we we are saying that Fg is assuming the role of F in F=ma

    or that F=Fg

    thus we can substitute ma for Fg to get

    ma = GMm/d^2

    cancel m on both sides of the equation and get

    a = GM/d^2, which tells us that the acceleration of m due to the gravitational attraction is independent of the magnitude of m's mass.

     

     

     

  6. 24 minutes ago, jajrussel said:

    This is where I got the word lift. Not arguing just saying. Not certain if I added this picture correctly? Guess I have to hit submit to find out… note it is not a link, just part of a screenshot.

    IMG_0029.thumb.jpeg.1214b95cf1725201835f633d67563d1c.jpeg

    As I already noted, 28,437 kph falls a bit below that for even a near surface orbit.   To be lifted off "into space", using the Kármán line (at 100 km altitude) for the boundary of space, you would need to be moving at 28,498.5 kph.  In which case, you would rise to a height of 100 km (the apogee of your orbit), and then drop back down to perigee at the surface, rise up to apogee...

    To leave the Earth's vicinity entirely, you'd need to be moving at 40,253 kph ( escape velocity)

  7. 15 minutes ago, jajrussel said:

    I read that Earth would have to spin at 28,437 km per hour to cause us to lift off the surface. I’m assuming at that point we would  effectively be weightless.  Seemingly throwing a wrench into F=GM1M2/R , so what effect would it have on the moon?

    1.  It is meaningless to say "spin at 28,437 km", as rotation needs to be measured as angular velocity. (deg/hr, rad/sec. etc.)

    I know that it is common to express this in terms of tangential speed( in this case, at the equator) But it is sloppy and can lead to misunderstanding. For example if the Earth had a tangential speed of 28,437 kph at the equator, then at 45 north latitude it would only be 20,105 kph

    As swansont has pointed out there is a speed where the centripetal force (the force required to keep an object moving in circle) and the gravitational force balance out. This would result in the object going into orbit around the Earth.   Gravity is still in play. In fact it is gravity that would prevent someone standing on the equator from just shooting out into space at in a straight line instead of just hovering over the Earth. And by the way, your number is a bit low, the equatorial speed would need to be 28463 kph

    And because of what I alluded to earlier, only someone on the equator would even go into orbit.  People elsewhere will feel lighter, and the ground would seem to tilt a bit under their feet ( And even this is an over simplification which assumes the Earth maintains its present shape.  If the Earth was indeed spinning this fast, its very shape would change, making it much more of an oblate spheroid. 

  8. 9 hours ago, AIkonoklazt said:

    I don't know about "GOP" but that asshat is still ahead in the polls (and always ahead when I check, which is why I usually don't check) https://projects.fivethirtyeight.com/polls/president-general/

    image.thumb.png.a9bbe1e734db5657792c2459f681d91a.png

    I wouldn't place too much faith in the polls; as of late, they have been shown to be highly unreliable.  Right up to the '22 midterms they were predicting a "Red wave" with Republicans making large gains in the House (60+ seats). In the Ohio election dealing with the Republicans attempt to change the requirements to alter the state constitution, the polls said it was close and could go either way, while in the election it was overwhelmingly rejected.  And most recently, a Democrat won in Florida in a red district when polls showed him losing.

    A lot of this can be put down to the polling methods not keeping up with the times and thus oversampling certain segments of the population and under-sampling others.

  9. 16 hours ago, TheVat said:

    Taft required a special bathtub installed in the WH.  Not sure what could be installed there in 2025 to remedy Trump's cognitive handicaps. Perhaps a trapdoor.  Biden I'm less worried about - maybe because I know his choices of veep, cabinet and support staff are sound and informed by decades of political experience.  

    While Trump will be sure to fill his administration with yes-men who's only qualifications are a sworn fealty to Trump. What little reining in and push-back he got last time will be nonexistent.

  10. 2 hours ago, kacenty said:

    ddt = dt/sqrt(1-GM/(r1*c^2)) - dt/sqrt(1-GM/(r2*c^2))

    for:

    dt = 86400 # seconds per day
    r1 = 6.36e6 # distance from center to surface of Earth
    r2 = 2.66e7 # distance from Earth's center to GPS

    ddt = +45.7e-6 # GPS clock gains 46 microseconds per day

    for:

    dt = 86400 # seconds per day
    r1 = 6.36e6 # distance from center to surface of Earth
    r2 = 1 # 1 meter from Earth's center

    ddt = -386 # clock at 1m from Earth's center lags by ~6.5min per day relative to surface

     

    Talking about time dilation and frequency shifts while there seems to be simple clock rate change.

    --- Edit 4 Feb 2024, 14:10:59 UTC ---

    One can ~force chat-gpt-4-1106-preview to admit that choosing between those three (time, freq, clock rate) shifts is a matter of concept.

    That would only be applicable if you were shrinking the Earth in order to keep all of its mass contained within a sphere with a radius of r as r decreased.

    As you move towards the center of the Earth this is not the case, as the amount of material within r decreases as you do so and thus M is not a constant throughout the trip. So while at the surface of the Earth Gravitational potential is -GME/rE, at the center, it is -1.5GME/rE 

    Thus the difference in gravitational potential between the surface of the Earth and its center is smaller than that between the surface and an infinite distance, and so would be the time dilation factor difference.

  11. 16 minutes ago, Phi for All said:

    Last year in Colorado, our state passed a law banning "ghost guns" that are 3D printed or sold as kits, which are untraceable. There's only one main reason somebody would want to own one of these: they don't want the gun traced back to them, so you'd think it's a no-brainer to ban them, right? Lawsuits have been filed against the state by gun lobbyists and shooting clubs who want the law struck down on principle. It's another "If we give you an inch, you'll take a mile" argument from inhumans who don't much care about mass murder and children dying in school.

    What kind of responsible gun owner would want unregulated, untraceable firearms being manufactured by anyone with an inexpensive printer?

    The argument you so often hear is that gun regulations won't stop gun violence.  It's the all or nothing approach; that if a regulation doesn't prevent all gun deaths of innocents, it shouldn't be enacted.  Saving 10 lives a year isn't worth it, nor is saving 100 or, 1000...

     

  12. 18 hours ago, Photon Guy said:

    None that I can think of, but the point is that just because the lightspeed barrier can't be broken by conventional means doesn't mean it can't be broken period. 

    As pzkpfw alluded to, If it requires a new, now unknown, physics to allow for FTL,  then it is pointless to speculate about what would happen, because we have no idea what rules we'd have to adhere to in this new physics.

  13. 37 minutes ago, StringJunky said:

    I think I read the other day Trump doesn't want the border fixing, he wants that to be his election issue. This seems to be why the GOP are in disarray; conflicting directions. 

    The Republicans have been playing this game with the border for years.  They have no interest in dealing with it, as fixing it would give them one less thing to complain about, and all they have to run on are grievance issues.

  14. Agreed,  the..

    18 hours ago, graybear13 said:

    notion of some primeval atom  from which everything (billions of galaxies) sprang forth in a split second

    is a silly one. Good thing for the big bang model that it doesn't claim this.

  15. On 1/13/2024 at 3:57 PM, Capiert said:

     


    Why would
     the Babylonians
     use 60 divisions,
     e.g.
     for minutes
     & seconds;
     & (=but) then (suddenly, break that pattern, &)
     divide the day
     into (only) 24 hours?



     

     

     

    They didn't.  The Babylonians divided the circle in 360 degrees. They then defined a "degree of time" as how long it took the Sun to travel 1 degree in the Sky, which they then divided into 60 minutes of 60 seconds each( we still see this in the practice of measuring angles in degree, minutes, seconds.) Thus the Babylonian minute and second were not the same duration as our modern one. 

    The division of the day into hours was an invention of the Greeks. It wasn't until the middle ages that the two systems were combined, making the hour divisible in the same way that the Babylonian degree of time was.

    So, there is no mystery, as it is the result of cobbling together two different time keeping systems.

  16. On 12/27/2023 at 6:17 AM, William.Walker39 said:

    According to Relativity, two inertial moving observers will see each others space contract and time dilate. This is a complete contradiction and a physical impossibility if the effects are real. Objects and the passage of time can not be both small and large at the ""SAME"" time for the ""SAME"" observer. The only possible explanation is that the observed effects are an optical illusion.

    It is not a contradiction, it just isn't compatible with the Newtonian model of time and space. And at its heart, Relativity uses a completely different model for these. In Relativity these measurements are not absolute but frame dependent.

    An analogy would be these images of two lines:

    lines1.png.cfd9f7e0988d1f3f4416c605219a0510.png

    lines2.png.5c04bfb326498197f1ee194de798afc1.png

    The same set of lines, just viewed from different perspectives.  In the first image the red line is "taller" than the green, and in the bottom image the green line is "taller" than the red.  The point being that in Relativity, time and space are measured more like the "height" of the lines in the images and not by their absolute length.

  17. And considering that the magnitude of High-Low tide cycle coincides with the phases of the Moon, as does the varying time period between successive low and high tides (which can vary a fair amount to either side of 12hrs), It seems a bit silly to brush away the influence the Moon has on the tidal cycle.

  18. On 11/24/2023 at 11:56 PM, Bjarne-7 said:

    Even a hen can find a nugget of gold

     

    But, does the hen recognize what it has found, or is it just a shiny rock that attracts it attention? And for the hen's purposes, a nugget of gold is less valuable than a small rock.  Chickens ingest these small rocks to hold in their gizzards, were they serve in lieu of teeth.  The contractions of the gizzard use the rocks to grind up the grain, etc. into small digestible  bits.  Gold, being a soft metal, serves as a poor substitute for common rocks. 

  19. You may "always hear that", but it isn't what model actually says.  All it says is that the Universe, in it's earliest stages, was extremely hot and dense, and says nothing about it's size.  One of the still unknowns about the universe is whether it is finite or infinite.  The references to being "smaller than a proton" likely are referring with the "observable universe",  which, for all we know, could be a tiny corner of a much vaster, or even infinite universe.

  20. 5 hours ago, Sensei said:

    ..and they never look the same as they did before, so every time you look at a nail like that, you are reminded of an accident from the past..

     

     

    That hasn't been my experience.  Both my thumbnails look perfectly normal, and you'd never guess that anything out of the ordinary had ever happened to them.

  21. 55 minutes ago, mistermack said:

    Can you get that in the mouth? I'd willingly chew some socks, if I could grow a new set of teeth. 

    Unfortunately, it isn't the fungus that causes the regrowth.  I talk from experience. Over my life I've lost two thumbnails, due to trauma, that then grew back.

  22. 1 hour ago, swansont said:

    Even the act of publishing doesn’t mean an idea is in its final form. Einstein published several papers, refining general relativity as he went. He was also wrong about QM.

     

    There is a neat story about Einstein concerning this.  This occurred during some scientific conference. Einstein and a few others were at a table debating QM. Einstein would come up with some problem that he felt disputed QM, and the others would go over it until they found a flaw with his argument.  Einstein finally came up with on that no one could find the flaw in. It started to get late, so they decided to call it a night.  They met up again the next day.  Whereupon Einstein stated that he'd been thinking about it, and had found the problem with his own argument.

  23. 2 hours ago, Chris Sawatsky said:

    and someone pointed out that he worked reviewing others work and put his theory together using others work,

    I fail to see where this would matter, other than Einstein taking credit for that which he was not due.  It has nothing to do the validity of the conclusions. And as pointed in the previous post, the theory has survived every test thrown at it, and much of the equipment we use today would not function if it were incorrect to any large degree.

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