41

Just Chat! / Re: There's a section with "similar topics" appearing.

« on: 13/04/2022 18:24:36 »

It's been there forever, and it seems to be a simple best-match on what it sees as keywords.

    The Similar topics suggested included:
a)   "Can I Use Washing Up Liquid To Wash Hands And Hand Soap To Wash Plates?"
b)   "How long must a prism-shaped corridor be to render a light-source invisible?"

The first one obviously matched 'plates', but no clue why it thought b) should be on the list.

42

Just Chat! / Re: A Short puzzle with dogs.

« on: 12/04/2022 19:23:44 »

The calculus appears pretty complicated, but the picture shows some trivial facts.
First, to answer a prior question, I assume everything is a point, the problem otherwise not really being fully defined.

You've approximately shown nearly half the distance traveled. At the actual point (har!) the distances between them have been halved, the answer is simply twice the distance already traveled.

The remaining distance is a square still, but rotated something like 30 degrees or so. Each time the distance is halved, the square gets rotated by that amount, so the dogs are going to circle each other an infinite number of times before the collision after a total path length.

My attempt: The problem can be broke into tiny pieces, so let's say a dog moves a trivial distance x, almost a straight line. It will curve just a little bit, but for sufficiently small x, a straight line, bringing it exactly x closer to the next dog. This leaves the same initial condition, but rotated and a little closer. Therefore the path length of each dog is exactly 1 by symmetry since each movement of x reduces the distance between them by x.

43

Physics, Astronomy & Cosmology / Re: Measure Time on Mars

« on: 11/04/2022 19:03:34 »

Thank you for your responses. But does the Sun move one degree per day on Mars like it does on Earth? I couldn't find the answer to this question easily.

By definition, the sun moves not at all (on average) from day to day, but it does move about one degree per sidereal day (of which there are ~366.¼ per year).  So if Mars has 640 sidereal days per Martian year, then the sun moves 1/640th of a circle (a bit over half a degree) per sidereal day. Per actual day, it doesn't move at all, again by definition.

On Mercury, despite it rotating the same direction as its orbit, the day is longer than its year, but the sidereal day is shorter that its year. The sun crosses the sky the wrong way, and stops its motion altogether and even moves backwards a little bit (same time every year) before continuing on its normal way, a funny sight to us, but just normal for anything there.

44

Geology, Palaeontology & Archaeology / Re: Did ancient builders suffer from respiratory disease?

« on: 11/04/2022 15:02:20 »

Just like modern life, where the majority cause of death now, at least in developed countries, tends to be things like cancer, heart attack and diabetes that cause the majority of non violent deaths

Agree. Even as recent as a century ago, any accident might leave a person sufficiently disabled to continue making a living, at which point death-by-poverty might result. Now the social system feeds them, but rarely with healthy foods, so the cancer and heart deaths rise to the top.
My father died of work-related toxins, but in his 70's, long after cessation of exposure to the toxins in question. My mother is quite healthy but with painful damage to her feet due to years of standing for work, and lifting that should have been done by others. Somehow I think the feet will be the eventual death of her. My relatives on her side have a habit of reaching their late 90's, so good stock there.

I expect to die of cancer if nothing else gets me first, due probably to a lifetime of preservatives in my diet.

45

General Science / Re: At what gravity does a person run the fastest?

« on: 07/04/2022 23:41:41 »

Found this:
--- "Reducing-gravity-takes-the-bounce-out-of-running"
A scientific study, with actual data collected, about the running stance and gait adopted in simulated low-G environments.

Their conclusions:  Mainly that the gait is adjusted so as to keep the centre of mass extremely flat and level, i.e. almost all bounce is removed.  Their models suggest this is energy efficient (they use "an impulsive model of running" developed by Rashevsky and Bekker - although these people contributed at different times and not collaboratively).

Cool link. I watched their vid, and they have guys running at about 2 m/sec, hardly an attempt at speed. It wasn't their point. The vid shows normal and moon gravity, but the data collected shows stuff up to about 2/3 g.

I'm not so sure about the energy-efficiency theory. Humans are already notoriously low efficiency when it comes to running. Most creatures of our mass use less than half the calories to maintain a specific pace.
The low-bounce gait helps them maintain the natural rhythm of a mild jogging pace. A bigger bounce would mean an uncomfortably slow rate at which the legs are swapped. At a faster running speed, the running gait would probably become completely unfeasible as the legs would have to move too quickly to match the speed of the ground under you, and there's little point to doing it one leg at a time.

The test as done cannot realistically simulate a real run since there is no wind resistance, as you point out. It's on a treadmill. Great for the sort of data they're collection though.

They didn't seem to have a wind fan or anything to re-create the effect of air resistance.

At 2 m/sec, it's effectively negligible anyway. People can walk far faster than that, but only at worse energy efficiency.
I'd love to see a speed walking race on the moon...

Just for amusement, here is Usain Bolt trying to sprint in low G:

A vomit comet vid. Yes, it's just fun. No practice or sustained gaits, and it's all acceleration, no actual speed, and they're wearing only socks.

Regards, and thanks for the on topic post, unlike the A/B twins...

Given infinite time what speed would he achieve.

Probably little different than at full gravity.

If 99.999etc of his energy was directed forward rather than up I surmise this must be fastest

It's not about energy, but about force. If all the force is directed forward, you'd perhaps go faster, but how exactly are you going to apply force that way, especially with socks on what looks like a vinyl padded mat. Those guys had nothing to give them any traction.

The ion drive doesn't have air resistance working against it. It's mean to be used in a weightless vacuum, an environment where an athlete would make zero progress at all by attempting to run. He may have all the energy he wants, but he has nothing against which to apply a force.

46

General Science / Re: At what gravity does a person run the fastest?

« on: 05/04/2022 15:26:07 »

Special skates going off the sides of the feet..

Special skates for people need to keep the blade centered on the leg, so my comment above is nonsense. It might be different for robots.
If a person wants to maximize horizontal thrust to lift ratio, one uses a taller skate such as is used by short-track racing, and not a skate with an off-center or tilted blade.

That reduces friction significantly (but not to zero, because then they would have no acceleration)

That's like suggesting that a rollerskater could not accelerate if the wheel-bearings were frictionless. Of course speed skaters strive for (however unattainable) zero friction in the direction of motion. That's the point.

On the Moon, the gravitational force on a human body is about 6 times less than on Earth, so this would require a skate contact area that is 6 times less - maybe 3 times shorter, and half of the width? (Assuming normal atmospheric pressure, so the ice doesn't sublimate.)[/quote]Again, disagree. To apply the corresponding pressure needed to melt the ice, it would be proportional to the force applied to the skate, not proportional to the weight of the skater. You're assuming the guy is just standing there, but he's applying much more force than that. A skater on the moon would want a much lower angle of attack to minimize upward lift, so the taller short-track skates would prevail. He might be able to apply (guessing) half the pressure that he does on Earth, so maybe half the contact area, but it would be an awkward gait. The optimal speed might be achieved by skating in a circle instead of a straight track.
Also, maybe a longer skate would help prevent slippage to the side.

I believe someone raised the point of the similarity with sailing dynamics as to forward motion gained from a side on wind.

Sailing utilizes energy from a difference in velocity of two different mediums. That makes it a poor analogy to skating where there's only the one medium and the work is done against one's own inertia rather than the second medium.

However, even in Mars gravity (that's what, 0.4g? ) You can't even perform a move, you must hop. There's just not enough friction to guarantee yourself a horizontal push.

Hopping is more efficient than walking, and running probably isn't viable at all, lacking a way to counter the torque of alternating legs being used in long strides. A horizontal push is not hard to do, but one sufficient to move quickly is difficult, yes.

The question is, could my max speed be higher at 0.9g or 1.1g?  Some gravity where running (for which we're evolved) still works. Where's the sweet spot?  I agree that 0.4g is probably too low and we'd be slower on Mars.

Any rise in gravity will raise the friction of your body, but not increase your inertia.

Agree, but how much is that friction useful once you're already up to speed?  That friction seems most useful only for the initial acceleration/cornering.

Also, there is the issue that gravity increases, resulting in greater atmospheric pressure.

4th time: Please read the OP and subsequent posts. No change in atmosphere.

This means that more air is pushing through, which slows your speed.

More time airborne between strides increases the duration that the air friction works against you. But the pressure is assumed invariant at any gravity.

Not everyone can run or move fast!

Besides the point. I'm talking about an average healthy person, and perhaps one who has had time to practice in the altered gravity, but not so much practice that his physiology has changed.

and a human can make faster decisions than a computer system.

Not so. A computer can react many times faster than can a human, and it has been that way for a while now. The playing card trick shows this: Have somebody hold a playing card vertical, with you holding your fingers a cm apart with the bottom edge of the card between them. When the person lets go of the card, trick is to clamp down, catching the card before it passes between your fingers. Apparently it's beyond human capability, but a robot can do it before it moves even a 10th of its height.

47

Physics, Astronomy & Cosmology / Re: How does a red-shift affect a black body spectrum?

« on: 05/04/2022 03:49:43 »

I think I agree with Origin's statement about the shape, but is the T2 shape of a stationary object just a shifted version of an object with a different temperature?  If not, then a shifted (as seen by a moving observer) object at T2 would not be the same shape as a stationary object with a 'proper temperature' (if there is such a term) of T2. I don't know my black body radiation enough to say one way or the other.

In the rest frame of the observer, is the radiation they receive from the black body still going to have the right distribution to be consistent with a Black body spectrum but just with a different temperature T2?

As for the statement above, the temp T2 is dependent not just on the frame, but the position of the observer in that frame.  So if the black body is moving at v in the +x direction, the observer (stationary in that frame) might see a red or blue shift depending on his position in that frame.
You know this, but the OP didn't make that clear. Maybe he's off to the side and the thing is going by him without any Doppler shift, at least for a moment, just like an ambulance going by momentarily has an unshifted pitch to its siren.

48

General Science / Re: At what gravity does a person run the fastest?

« on: 03/04/2022 20:44:23 »

As I said earlier, if g < 0.2g_earth then the total pressure won't inflate your lungs adequately even with 100% oxygen. If g>>g_earth you may have problems with nitrogen dissolving in your blood  - not sure how this affects the ability to exercise but any divers may have an opinion.

Pressure and oxygen level is being held normal at any g, per the OP. Why do I have to say this a third time?
Think of the test being performed on a pressurized space station with a large thin wheel (large enough that it's locally pretty flat) for the track. The atmosphere is unaffected by spinning the wheel at different rates.

49

General Science / Re: At what gravity does a person run the fastest?

« on: 03/04/2022 19:16:58 »

I've had a quick glance at whats on the web.   A similar question has been asked on Quora and Reddit.
https://www.quora.com/Is-it-possible-to-run-very-fast-in-a-low-gravity-environment
https://www.reddit.com/r/askscience/comments/j4ss3/which_would_be_the_ideal_amount_of_gravity_to_run/

I looked through these. A lot of similar responses, and further exploration into the matter seems to require some actual tests or a good simulation or something.
A lot of the same mistakes were made as well in the responses, like assertions of gravity-dependent atmosphere when the OP clearly specified this to be normal.

You'd need to modify the atmosphere of your g--altered planet.

Yea, like that. Read the OP Alan. The atmosphere is normal, by whatever means necessary.

Also, many seem to miss where I stated in my OP that this question is about max speed, not max acceleration.

Bikes have gears which would account for the faster speed

So do skates, as I pointed out in post 9. The 'gear' of a skater is the angle of the skate relative to the direction of motion, almost perpendicular at first, but almost parallel as the higher speeds are achieved.

50

Physics, Astronomy & Cosmology / Re: How does time dilation work?

« on: 03/04/2022 00:59:08 »

Mike, I've moved your last three comments to your own thread here:
https://www.thenakedscientists.com/forum/index.php?topic=82459.msg673920#msg673920
There are holes in your ideas, and I can respond to them better over there.

The main sections are not for personal theories. I will reply to this bit below.

Anybody is free to use any coordinate system they want, and if they both choose the same coordinate system, then they'll agree about their respective ages at all times.

At any given instant "tau" in the life of a given INERTIAL observer (he), it's clear that there is just a single answer to the question "How old is that particular distant person (she) right now (at the given time "tau" in the life of the inertial
observer)

This assertion denies the theory of relativity which has relativity of simultaneity: The present time of any distant worldline ('her' worldline) relative to a given event (a particular time on 'his' worldline) is frame dependent, and this follows fairly trivially from the premises of the theory. Under SR, no frame is better than any other.
Your language is very absolutist (frequently lacking in frame references) leaving it very difficult to understand, but you don't seem to be an absolutist yourself since you don't deny constant speed of light that the absolutists do, and you don't reference a universal frame, but rather one relative to a particular observer, but then neglecting to qualify most statements with this relation.

So please confine the evangelizing of your simultaneity method to your own topics and don't preach them in other people's topics in the main section.

51

Plant Sciences, Zoology & Evolution / Re: Can A Cuttlefish Act As A Video display ?

« on: 02/04/2022 17:13:29 »

Is he capable of HD ? 4K ?

Sadly, in the case of Henry, it's just 720i, enough for DVD at least.

52

Plant Sciences, Zoology & Evolution / Re: Can A Cuttlefish Act As A Video display ?

« on: 02/04/2022 16:03:26 »

I think he already is one. Like his squiddity relatives, he can put on a video of his background for camouflage, put on a scary show for what's considering him for lunch, or maybe a sexy vid to get the ladies (like he needs that... already cute enough to want anybody to cuddle a cuttlefish). Only trick left is to pick up the wifi so he can stream netflix or something.

53

Physics, Astronomy & Cosmology / Re: How does time dilation work?

« on: 01/04/2022 13:47:09 »

I would just add [...] that the two twins generally don't agree (and don't have to agree) about their respective ages when they are separated.  They obviously MUST agree when they are co-located, and they do.

Anybody is free to use any coordinate system they want, and if they both choose the same coordinate system, then they'll agree about their respective ages at all times. So for instance, when I'm in the car traveling to Grandma's house, I'm moving relative to Grandma, but both of us probably choose the coordinate system of the ground below us and hence are not in disagreement about our respective ages even while spatially separated.

If they're co-located, then they'll agree even if they choose different coordinate systems.

Clocks in the opposite direction run BACKWARDS!

Are they moving faster than light?

Mike very frequently omits his frame references and spews statements that sound absolute when they're just coordinate effects. The above statement also makes it sound like anything behind you runs backwards when you're accelerating, which is wrong. Only sufficiently distant clocks run backwards, and only relative to the accelerating coordinate system.

So to clarify:
Relative to an accelerating coordinate system (or accelerated reference frame, ARF) of a given object (say a pilot and his clock on a ship), time 'runs' faster in the direction of acceleration and slower behind. For a given fixed proper acceleration, an event horizon forms a certain distance behind (called a Rindler horizon) beyond which time can be said to run backwards. Anything closer than that at it runs slower, but still forward. Mike omits all that of course.

So for instance, suppose I'm the pilot in the middle of a ship that is kind of long and am stationary relative to Earth, 100 light years away. I've been visiting planet Zog which is currently half a light year away in the direction of Earth, also stationary, and planet Vavoom, 1.2 light years in that direction.  At time zero (on everybody's clocks), I begin acceleration at 1 g (constant proper acceleration as measured at the middle of the ship where I am) away from Earth and those other planets. As measured in my accelerated reference frame (ARF), Zog will drop away, increasing its distance from me, and its clocks will run slower.  At 1g, the Rindler horizon forms at about one light year behind me.  Zog will never pass through this no matter how long I accelerate. As it approaches the event horizon, its clocks will slow arbitrarily close to zero and never get there, just like dropping Zog into a black hole.
The Zog people don't care. It's just a coordinate effect, nothing that actually affects them.

Vavoom is already on the other side of the event horizon, so relative to the ARF, its clocks run backwards, but its speed (the rate of changing distance between me and it as measured by my clock) is fairly tame, well under c.

Earth is really far away, and relative to the ARF, its clocks run backwards very quickly, and Earth indeed moves well faster than c, and in my direction no less, so it's getting closer.

So after say two years (as measured by the accelerating pilot clock), the engines turn off, putting me in a new inertial frame relative to which I am stationary and all those planets are moving at 0.9682c away from me. But how close are they at the moment the acceleration stopped?

Zog was 0.5 LY away, and now its 0.85 LY away, more distant, but still closer than where the event horizon was.  Vavoom is 1.026 LY away, closer than the 1.2 it was before, but it took two years to move that short distance. Earth on the other hand is now only 25.725 LY away, meaning it moved over 74 light years closer in only two years, so yea, that's faster than c, but not 'faster than light' since no light is being outrun. The time on Earth is currently about 95.88 years earlier than time zero when I left, so time there very much did run backwards in the ARF. In short, Earth is moving away from me, but for negative time (relative to the ARF), so that brings it closer.

Things moving at a coordinate speed faster than c is commonplace for non-inertial coordinate systems. For instance, relative to the frame of my mailbox, Neptune goes around it once a day tracing a path a bit longer than a light day, meaning Neptune moves faster than c relative to my mailbox, but only relative to the rotating frame in which my mailbox is stationary, not relative to any inertial frame. There's no inertial frame in which my mailbox is stationary, and there's no inertial frame in which any star, however distant, is moving away from us at a rate over c.

54

General Science / Re: At what gravity does a person run the fastest?

« on: 01/04/2022 03:16:40 »

The majority seem to think a slightly higher g environment would help.  At least that's their opinion for a 100m sprint where acceleration is everything.

Ah, but I'm assuming you're already up to speed. 'How fast can you run at such and such g', which is a different question than  'How quickly can you cover short distance X from a stop at such and such g'. Hence my hesitation about the claws/cleat which help only with acceleration, not speed, at least not near 1g.

Thanks for the reply. I'll look at the posts, but I hesitate to get any answers from quora.

I did think about why bikes are faster than skating. Biking seems almost 100% efficient, almost all the mechanical energy going into forward thrust, whereas the skater is thrusting against his own inertia, sending his center of gravity from side to side. That's a lot of work, even though half of it is negative work being done. The human body doesn't capture negative work very well. Again, a kangaroo does. They're designed to absorb the energy of coming down and bounce back up again, using energy only to add to it a bit. Hence the skater wasting a lot of energy that the cyclist doesn't.

55

General Science / Re: At what gravity does a person run the fastest?

« on: 01/04/2022 00:35:50 »

Thank you for all your replies. There are no hard rules, but obviously vehicles (powered cars and such) are pointless to ponder.

There seems to be categories of responses:

Traction:
PetroC and Alan mentioned actively gripping the surface if static friction isn't enough. Cleats/claws helps greatly with acceleration. Do they help with speed?  At low enough gravity, they have to, else any effort expended 'running' is going to put you in the air most of the time. Limited time in contact with the ground requires maximum thrust while you're down there, so they very much help with speed and not just acceleration, which is what they're used for at 1g.


Optimal at 1G

Straight off the bat you would have thought it was something close to 1g.

My guess (like others) is that we are probably pretty close to optimal for 1G.

Kangaroos also evolved in 1g, but jumping does seem to be more efficient in low g.

As for an optimal gait at low g, a rolling hop seems natural for humans. The spacemen landed on a rear leg and rolled to the front one in a hop, keeping one leg always forward. This is very similar to a horse canter which is a roll using all four legs in turn, then going airborne. A horse has four different gaits and it's interesting to see where each is optimal.

But the main thing is the optimal-at-1g comments. All creatures have evolved under 1g and are presumably the optimal form for that creature at 1g, but while that might mean that a different form might have evolved at a different gravity, it does not follow that 1g is necessarily optimal for the speed of a given creature in its Earth form.  I suspect a person could run faster (maybe not accelerate harder) under lower gravity, but not under a lot lower gravity. There's a sweet spot somewhere for each creature and it isn't 1g.  The cheetah needs those claws for good acceleration/cornering just like the cleats for sports, but do they help with speed? Might a cheetah run faster given greater traction at 1.2g?  I don't know. Few creatures are limited by traction while running at a stead speed in a straight line.


Not running

The 1000m speed skating record is roughly twice as fast as the 1000m running record.

Human are notoriously inefficient runners. We have massive legs with the muscles far too far down from the hips, as compared to the pencilly legs of deer, cows and birds. All the meat is up in the haunches that barely move, and the part that does move is relatively light stilts.
So yea, it makes sense that a human can move faster via different means like skating (ice or wheels), or via bicycle or something.

54 km/hr is the skating record, which seems awfully slow to me. I can (could anyway) better than that on a bicycle, and I'm no Olympian. Both kinds of skates maximize static friction in one direction and minimize kinetic friction in the orthogonal direction. Both skates and bicycle can select an optimal gear for optimal transfer of work to the surface. They all seem bound pretty much by air friction, so why is the bicycle so much faster? I don't wear a slick air-suit when cycling, and yet I do better than the professional skaters on level ground.  Any ideas anybody?  Is there something inherently more efficient about pumping pedals in a circular motion rather than thrusting feet to the sides? Both are doing the main work by pushing feet down, just like in running. The cyclist doesn't extend the leg all the way like the skater does, but the cyclist can also pull on the upswing, using less natural muscles.
Any ideas?

OK, back to low g: Can a skater or cyclist go faster on the moon, or at 0.8g, or 1.2g?  Just like running, it doesn't seem to be limited by friction. If I run harder, my feet don't slip. But on the moon? Yes, friction would be a big issue and slippage would prevent full thrust.
A hard-working skater would go airborne. There only alternative is to get super low and thrust almost parallel to the ground so there's minimum upward force. Special skates going off the sides of the feet would have to be designed not to slip despite the low weight on them.
The cyclist can have a very long wheelbase to prevent 'wheelies', but something like studded tires are going to be needed to transfer sufficient thrust to the ground. 0.16g is just not enough to get proper traction. Suction cups maybe??? That can't help your speed. Imagine trying to coast with suction cup tires.

56

Just Chat! / Re: What is your main area of interest or expertise?

« on: 31/03/2022 17:25:53 »

I'm going to give the award of the "best answer" in a couple of days.  If you want a chance to win this greatly coveted award then get your replies in soon.

This topic is more of a survey and not a question where there are answers more correct than others, so I'm not sure of the meaning of one of them being the best. Is one person's interest/expertise better than another?

Secondly, I suspect you overestimate the level at which that 'best answer' status is coveted. Saying thanks to all replyers is often more appropriate, and something where the 'score' is kept as well.

Best regards

57

General Science / Re: At what gravity does a person run the fastest?

« on: 30/03/2022 21:38:39 »

Didn't Allan Shepherd hit a golf ball on the Moon? That probably went pretty far, pretty fast!

Pretty far, yes, but not particularly fast. It went far not due to its speed, but due to lack of both gravity bringing it down quickly, and air resistance slowing it as it goes.  I doubt the shot was even half the speed of a typical tee shot on Earth, especially given the cumbersome suit being worn at the time.

Yes, I'm restricting the question to life forms under power of legs, not ballistic objects or vehicles, the ground speed of which is limited only by orbital speed. Yes, one can actually run off Deimos if you can conjure the purchase needed to get up to what would be a running speed on Earth, about a third faster than our guy trying to cancel the moon rotation. The purchase can be had by erecting a circular arch, sort of like a hotwheel loop. Going around that gets you the artificial gravity needed to actually utilize your legs.  For the purpose of the post, we're assuming speed on level ground, not using the artificial gravity of our runner's own centrifugal force.

58

General Science / At what gravity does a person run the fastest?

« on: 30/03/2022 16:23:37 »

The question came up given the realization that if one was on the equator of the moon, one could remain stationary relative to the inertial frame of the moon by running west at about 15 km/hr, which I can still do, albeit not for any extended time.

But I can run that fast here on Earth, not on the moon. Too little gravity up there, and hopping seems the idea method of locomotion up there, and we're not evolved to hop.

So given flat ground, normal atmosphere, and standard running attire (no shoes with wheels or springs), at what gravity (expressed as a fraction of g) can one run the fastest?  Too little and each step takes you airborne with a high probability of not landing on your feet, and with way too much air friction between bounces.  Too high and you'd barely be able to walk without breaking bones.

While we're at it, what sort of physiology has an optimal speed at higher or lower gravity?  Only ground-locomotion counts, not birds or fish or anything which utilizes the medium instead of the ground. I imagine ants could go faster in higher g, Maybe kangaroos would work better at lower g, especially if they could use their tail to maintain proper orientation in flight. They already go 50 km/hr (sustained), and in low enough gravity could probably outrun a cheetah (80, sprint)..

59

Just Chat! / Re: What is your main area of interest or expertise?

« on: 30/03/2022 13:25:25 »

My main interests are identification of irrational biases, things people take for granted without ever really justifying them. I tend to discuss such things elsewhere as this is a science site.

My limited expertise seems to be in relativity, quantum interpretations, and logical reasoning, as such expertise is required in the pursuit of the above, but I'm by no means an actual expert in any of it. My knowledge is weak in electromagnetism, and I avoid answering questions there. I am here mostly to answer questions coming from the rare poster that actually seems interested in learning.

You (ES) have probably already figured out most of that, except probably the bit about the biases.

60

Question of the Week / Re: QOTW 22.03.21 Does relativity make rocks on the moon older than Earth rocks?

« on: 27/03/2022 13:32:53 »

If I recall correctly, proximity to the sun is sufficient to put the planets in the right order of time dilation that would apply on their surface from Mercury to Pluto - their own individual mass, radius, rotation and orbit speed makes just a small contribution.

Rotation speed is completely insignificant compared to orbital speed, and even that makes terribly little difference compared to the varying potentials.

Sorted by slowest to fastest clocks on the surface of each planet, the list is:
Mercury, Jupiter, Venus, Earth, Saturn, Mars, Neptune, Uranus, Pluto

The standard reference for this data, including many of the moons, is Randall Munroe who yes, did all the mathematics for xkcd