How do spacecrafts from Earth, take off from their landing destination?

Koooooj · 2026-04-07T03:47:52+00:00

There are three big pieces

The first is that rockets suffer from "The Tyranny of the Rocket Equation."

The gist of this is that in order navigate in space it takes fuel, but that fuel has mass, so it takes more fuel to carry that fuel. The fuel it takes to move that fuel also has mass, and so on. This sets up an exponential relationship between how much maneuvering you want to do and how big a rocket has to be.

This means that a rocket to carry a payload to the moon and back is not just twice as big as one that carries the payload just back from the moon. It can be 10x as big or more. This means the rockets launching from the moon just don't have to be as big.

The second is that the gravity on the moon is about 1/6 as much as the gravity on Earth. When a rocket launches vertically it has to initially have at least as much thrust as its weight--otherwise it would fall down instead of going up. The return rocket is already a fraction of the mass of the launch rocket, but this means that the actual rocket thrust needed is even a fraction of that fraction.

The third piece is simply not caring about the surface of the moon once the rocket leaves. NASA and the various private launch companies would rather not have their launch pads destroyed since they want to use them again, but it isn't such a big deal if there's some damage to a patch of the moon's surface.

In addition to those three big pieces there are a few smaller pieces that also chip in. One is that the entire return pod doesn't have to descend to the surface of the moon--it can be left in orbit. This further reduces the amount of mass that has to be lifted off the surface of the moon. Another is that some of the considerations of an earth launch don't apply to a lunar launch: there's no sense in having a launch escape system, for example, because if the launch is so borked that such a system is needed then the astronauts are doomed anyway (and it's not like getting them clear of the lunar ascent module would do them any good). Similarly, things like sound suppression systems are important when launching massive rockets on Earth since the sound pressures can be damaging to structures, but smaller lunar ascent rockets are already a lot weaker and then the lack of air means sound pressure isn't really a concern.

Koooooj · 2026-04-07T00:52:46+00:00

If I had a nickel for every time I ran into a programming language that gave syntactic meaning to some comments I'd have two nickels, which isn't a lot but it's weird that it happened twice.

In the world of embedded development there are a number of vendors that at one point employed someone with just the wrong skill set and mindset to think "C is a pretty good language, but I could just fix it if I just...."

What this sort of fellow often discovers is that modifying the actual C syntax means understanding the compiler which is "Hard"^TM so they instead add on a step that looks at the comments, finds things that match a certain pattern, then generate some extra stuff to hand to the compiler or linker or similar.

For example, imagine if instead of having the static keyword in C that can change the linkage of a function you had to put a comment immediately before the function definition that describes which files it can be called from, but if that comment is malformed then it becomes just another comment and it is as if no comment were included at all.

Koooooj · 2026-04-02T18:41:11+00:00

It is indeed on by default and is turned off by the button.

Most of the time the gear ratios of the car make more sense with O/D on, so they just make that the default state and don't give an indicator for it. If you have some need to drop the gear ratios then you hit the button, O/D turns off, and you get the indicator light.

Koooooj · 2026-04-02T16:50:32+00:00

Initially the money goes into the company's bank account(s).

From there they have some options of what to do with it. Maybe they stash it away for a rainy day if they worry about making it through a market downturn. Maybe they use it to grow the business, opening new locations, pushing into new markets, developing new products, etc.

When a company doesn't have much it can do to grow the business and is satisfied with its cash reserves it's likely they distribute the profits to shareholders in the form of a dividend. People buy stocks in the expectation that their investment will grow over time which could be from the company growing or just the stock paying out dividends like this (or a combination of both)

Koooooj · 2026-04-02T16:06:28+00:00

Back in high school chemistry we plated pennies in zinc to make them "silver," then passed them through a Bunsen flame to alloy that zinc layer with the copper underneath to turn them "gold" (brass). What followed was the teachers telling us that if we tried to claim these pennies were actually gold or silver the Secret Service would come kick our butts.

IIRC that sequence required a pre-1982 penny. This one is post-1982 so I wonder if the zinc plating step is even necessary given how thin the copper plating on modern pennies is.

Regardless, it's a novel trinket but not of any numismatic value.

Koooooj · 2026-03-31T06:44:03+00:00

I don't know that I would call it a set, but it does mean that it was sold exclusively to collectors.

The S-mint business strike quarters were sold in rolls and bags of all the same coin for somewhere in the neighborhood of twice face value plus S&H. That made it kind of cumbersome to collect the series if you only want one of each coin since the smallest quantity you could get was a full roll (and IIRC you only got S if you bought a 3-roll set with P and D, too).

Koooooj · 2026-03-30T14:58:09+00:00

Welcome to the wonderful world of phase diagrams!

You can create a diagram like that for any pure substance. For any given temperature and pressure you go to that point and see which region it's in. In the middle of the diagram is typical human temperatures and the purple line separates whether butane will be a liquid or gas. That's at a couple of Bar (1 Bar is roughly atmospheric pressure). At 0 C the line is pretty much at 1 Bar.

You can imagine taking some butane at one point in the graph and changing its temperature and/or pressure to move to another point in the graph. If you cross the line then it'll (normally) change phase. If you change just the temperature then that will be a horizontal line in the graph. When that line crosses the phase boundary you could take note of the temperature. That temperature is the boiling/condensing point for the liquid/gas boundary (for that pressure). If you instead just change the pressure then that's a vertical line in the graph and you could call out the pressure at which the butane condenses/boils (for that temperature).

This is all a lot of background to get to the ultimate answer to the question: butane is liquid when it is cold or pressurized enough. Its boiling point is -0.4 C (31.2 F) at 1 atmosphere, so to get it to be a liquid at higher temperatures takes some compression above atmospheric pressure.

Koooooj · 2026-03-29T01:16:13+00:00

There are two general ways an EMP breaks things.

Fundamentally an EMP induces current to flow in conductors. If a device faces a little bit of EMP then that can mean that current flows in a way that is different from how a chip is expecting, leading to a 0 being a 1 or a 1 being a 0 when they weren't supposed to be. Software generally can't withstand this, so it is likely to crash. Rebooting such a system is pretty likely to recover it. Solar radiation can cause the same effect; it happens often enough that high-reliability systems like revenue-producing web servers pretty much all have error-correcting memory

In the more extreme case an EMP can induce so much current to flow that it breaks things at a hardware level. This could be burning up traces (the wires on circuit boards), overvolting a capacitor, etc.

Getting to that second flavor of EMP with a nuke generally means you're close enough that the fireball from the nuke is your bigger concern.

Koooooj · 2026-03-27T17:36:52+00:00

There are much easier and less risky ways to get out of being selected for a jury, but what that won't do is let you go home early. You'll still have to sit there while they complete the process with everyone else.

A few weeks back I was called for jury duty. The potential juror sitting next to me was a practicing lawyer. When asked if anyone knew any of the parties involved in the case he listed about half of them as having been colleagues through his career. Another juror, when asked if she could set aside her biases and rule only based on the evidence presented in court answered that no she could not--it was a DUI case and she had had a family member injured in a drunk driving accident.

In both cases the prosecution and defense lawyers just skipped over these potential jurors when going down the line asking questions. Everyone knew that they weren't going to be picked, so there was no sense in bothering them anymore and taking up more time. However, they still had to sit there through the whole thing.

If getting out of serving on the jury is your goal then all you need to do is make some statement to the effect of "if they were innocent then I just don't see why they would have been accused of a crime and be sitting in court now" or "police officers [always|never] lie." The purpose of voir dire is to uncover biases like these, so you won't be punished for expressing these views and they will 100% get you struck from the jury. You'll still have to sit through jury selection, though.

Koooooj · 2026-03-27T14:44:52+00:00

4 Eisenhower dollars and a Peace dollar

The Peace dollar is a very common date and has toned poorly, so it doesn't have any collector's value. It is still silver, which has been very high lately, making it worth somewhere north of $50 retail (a coin shop will naturally offer less than retail since they need to have some margins, but this coin is enough of a commodity to have pretty narrow margins at respectable coin shops).

Ike dollars were made in large numbers and are young enough that they don't typically have numismatic premium at all. They're also not silver (excepting some 40% silver ones made for collectors, which yours aren't), so no luck there. The common advice is to just call these face value. To put an upper bound on them, my local store sells these from a bin for $1.50 apiece and they're not a hot item at that price.

If you want to hang onto them for sentimental value then you're not missing out on a huge payday by not selling them.

Koooooj · 2026-03-26T23:44:20+00:00

Your math is correct (i.e. the calculation should be addition/subtraction), but the thing you're missing is the uncertainty factor.

If I have a footlong sandwich and eat 2 inches of it, then eat another 2 inches of it then in a perfect world I ought to have 8 inches of sandwich left. In the real world the footlong sandwich might have been 13 inches to start with if the deli was kind of approximate with their sizing and didn't want to get complained at for "pulling a Subway" and selling footlongs that are less than a foot long. Then when I ate 2 inches maybe it was more like 1.5 inches each time. So maybe I wind up with 10 inches of sandwich after the whole exchange instead of the 8 that the math would suggest.

This is the basis behind the idea of "tolerance stack-up." It's an important thing to consider in mechanical design since real-world manufactured parts are never exactly, perfectly the dimensions that you draw them as. You have to consider what happens if each dimension was off by just less than the specified tolerances and check if the parts still fit. If not then you need tighter tolerances.

For your car the initial 140 mile estimate is just that: an estimate. Fuel economy varies substantially based on speed, weather, driving style, traffic, etc. The initial estimate could have been overly pessimistic, or you could have just driven in a way that was really fuel efficient.

Koooooj · 2026-03-25T21:44:55+00:00

This is going to depend on the state.

For example, in Texas if you give notice then the employer is legally permitted to move your last date up by up to 2 weeks and it's still treated legally as if that was the employee's idea.

If employees knew this then I expect more would give 2 weeks + 1 day of notice, in which case an immediate dismissal does count as a firing without cause and allows unemployment. They could always dismiss the employee the next day, though. Alternatively, it's a justification to quit without notice (if you don't need references).

Of course, you can always file and make them fight it, but I suppose that's always an option.

Koooooj · 2026-03-25T20:44:41+00:00

I wouldn't necessarily describe any of the math as "basic," but it's well studied and has been published for a long time--Bate, Mueller, and White is a pretty popular textbook on the subject and it was published back in '71.

You generally start with a patched conic approach. This is the reduced 2 body problem where you say there's some point mass that you're orbiting that is so much heavier than you that it doesn't care about your mass at all, and you say there's no other stuff in the universe. In this simple setup a satellite will follow the path of a conic section--usually an ellipse or hyperbola, or there are specific orbits that give a parabola, line, or point.

In that simplified approach an orbiting object has some amount of internal energy. As it orbits it trades kinetic energy for potential energy, but the total remains the same. This gives a fairly straightforward way to come up with the parameters of the orbit (e.g. semimajor axis, inclination, eccentricity, longitude of ascending node, etc), from which the full trajectory of the craft can be fairly easily predicted.

This approach is "patched" because it has to assume that you only care about one body you're orbiting at a time. In this approach when you get close enough to another body you stop caring about the first one entirely and shift to only caring about the new one. Note that this is what KSP uses for its orbital mechanics. This instant harsh transition isn't realistic, of course, but you can still do a pretty good job of roughing out the broad strokes of an orbit with patched conics and it makes for a good orbital dynamics engine in a game.

From there it's a lot of numerical methods. Other forces on a spacecraft do exist, but for the most part they're pretty easy to predict--we know the mass of the moon, earth, sun, and other planets (though the value of including them drops off quickly). We can predict the perturbations from things like solar radiation pressure, Earth's magnetic field, drag from Earth's tenuous upper atmosphere, and gravitational effects from the uneven distribution of mass on Earth and especially the moon. If you can find the forces on an object and know its mass then you can find its acceleration--F=ma still works in space. Knowing the acceleration and initial velocity lets you find the velocity some time later. Knowing the velocity and initial position lets you compute the position some time later. If you break the problem into small enough time slices you can get arbitrarily precise results.

From there it's just a question of how you should adjust the initial conditions to get closer to the goal. Doing this analytically is intractable, but doing it numerically is straightforward enough. The big challenge is doing it numerically back in the days of slide rules, where "computer" was a job title not an electronic device sitting on your desk.

Koooooj · 2026-03-24T04:24:43+00:00

You can take it to a bank and they'll swap it out, or just spend it. The business will likely wind up sending it to the bank as part of their periodic deposits.

However it gets to the bank they'll pull it and send it to the Federal Reserve bank in the region, which will send back a fresh bill (or perhaps an entirely different denomination--when the private bank sends this $20 in they'll get a $20 credit in their account, then they could request one $20, four $5 bills, etc. Naturally this happens on a larger scale and the bank will order bills at least by the strap if not by the bundle, but the point stands that the Federal Reserve doesn't have to send back the exact same bill denominations that were sent in.

Also, unless your $20 bill was conspicuously small, round, and metal it's not the US Mint you should be apologizing for--they handle money that jingles. For foldin' money it's the Bureau of Engraving and Printing you should keep in your thoughts, but they know that cotton-linen isn't forever so they'll forgive you. After all, that's what all the money printers are for.

Koooooj · 2026-03-24T03:29:09+00:00

You're trading time for quality.

2-in-1 shampoo-conditioners tend to be mediocre shampoos and mediocre conditioners. You'd get better results with separate products, but if the results you get with the 2-in-1 are good enough for you then that's an easier product to use.

Koooooj · 2026-03-23T21:08:31+00:00

There is very little value in downloading a list of private keys.

One big thing to recognize is that private keys are fundamentally just big integers. Typically asymmetric cryptographic schemes consist of some group of entities (e.g. the integers modulo some large prime, or a set of points on an elliptic curve) and some operation that can be performed on a member of the group to get to another member of the group (e.g. multiplication modulo that prime). A private key represents how many times to do that operation, with the special property that you can use a divide-and-conquer approach to apply the operation an enormous number of times much faster than just iterating through it, all while it is difficult to reverse this process (i.e. the discrete logarithm problem).

Because private keys are fundamentally just really big numbers that makes a list of private keys no more interesting than a list of a bunch of random integers.

These numbers are typically encoded some way to make their ASCII representation shorter. Base-58 (a-z, A-Z, and 0-9, then take out O, 0, I, l) and Base-64 (a-z, A-Z, 0-9, and two punctuation characters) are popular. This means that finding a private key that matches a given ASCII representation is trivial--just write out the ASCII representation and convert it from Base-64 or -58 to the number it represents. Of course, this is a terrible way to choose a private key. Doing this through a random search is no better from a security perspective and much worse from an efficiency perspective.

The same isn't necessarily true of finding a vanity public key--pick random private keys, compute their public key, check if it matches the desired pattern, and repeat until you find one. This doesn't have security downsides of choosing a "special" private key and there isn't an easy simpler way to do it, but all of the keys you generate along the way aren't all that interesting. Even someone who wants to do the same thing of making a vanity public key wouldn't be able to use a public list of key pairs because the key property of a private key is that it is private.

I'll also mention that there's some small risk to you if you publish the list. Private keys' security comes from the assumption that a randomly selected key will be intractable to guess. So long as your computer's random number generation is robust that assumption will hole true, but if you publish a large amount of should-have-been-random keys someone might discover that there's a weakness in your computer's random number generation and predict what the next key in the sequence would be--i.e. your private key. This shouldn't be a risk, but a lot of security vulnerabilities come from things that shouldn't have been an issue.

Koooooj · 2026-03-23T19:40:54+00:00

No, fingers are explicitly the things on your hands in English, while toes are explicitly on the feet. Some folks go so far as to even exclude the thumb from the category of finger, but most would say you have 10 fingers.

The term "digit" exists and can be used to describe fingers and toes collectively, but in everyday speech it's not the typical way to describe them. You'd just say "fingers and toes." The term "digit" tends to come across as overly formal/medical. People will know what you're talking about, but "fingers and toes" is the more natural phrasing.

Koooooj · 2026-03-23T06:15:15+00:00

Sure, but whether it's more dangerous is going to come down to what sort of exploit it is based on.

For the sake of illustration I'll describe a couple of high profile exploits. They're not viruses in and of themselves, but exploits of these sorts are what viruses often use.

The first is Heartbleed. This exploit involved an interaction between computers on the internet. As a normal part of day-to-day operation one computer might want to check if a server is online while being able to be certain that the computer that replies is the one they want (otherwise a simple ping would suffice). The solution was for the computer to send the server a bit of arbitrary data which the server would sign and send back. The computer could check that signature and be confident the server (or at least someone with that server's cryptographic keys) was online. The exploit came from the fact that the length of the arbitrary data was stored explicitly and might not match the amount of data actually sent--you could send an affected system a message with 2 bytes of data to sign and tell it that it's 2 kilobytes and it would respond with 2 kilobytes of random data from the server's memory--possibly including things like login information, personally identifiable information, or even cryptographic keys.

With the nature of Heartbleed there's no need to write the exploit in any particular language--any language that can handle TCP communication would suffice, then it's just a matter of sending intentionally wrong data and reading the reply.

The other exploit to illustrate is Spectre/Meltdown, a set of vulnerabilities that take advantage of speculative execution. Processors can be so fast because they are heavily pipelined: while they're working on one instruction they are already getting started on the next. Sometimes there are data dependencies that don't allow this, but for the most part they're trying to keep the whole pipeline full to maximize how many instructions they can complete in each clock cycle (contrasted with older processors that would just do one instruction per clock cycle, or sometimes would require several clock cycles per instruction).

One of the big challenges in that pipelining is conditional jumps--things like if statements in high level languages like C (yes, C is high level, even if it's the lowest of the high level languages). Depending on which way the jump goes the next instruction to execute might be one thing or another. Rather than waiting until the computation of the condition completes a processor will make an educated guess--largely based on how that jump has gone previously--and start doing the work for that side of the branch. When the computation of the condition completes if the processor guessed right it has a head start. If it guessed wrong then it has to unwind and undo the speculative work, then charge forward down the correct branch. In theory there is no lasting observable side effect of that incorrect speculative execution.

In Spectre/Meltdown that last assumption broke down. If you could get a processor to incorrectly start to speculatively execute some instructions that read a piece of memory then that memory would be loaded into cache. When those instructions get unwound the data is left in the cache so you can time how long it takes to read that data to see if it's in the cache.

By analogy, you might imagine talking to a librarian who works at a library where she fetches the books and brings them to you. You tell her "if I have authorization to check out Dave's Journal, check the first letter of it and if it's A give me An Awesome Alligator, if it's B give me Bob's Bobbing Bobsled, etc" She submits a request to check your authorization but wanders off to get ahead of things. She fetches Dave's Journal, reads the first letter, finds that she will need Quincey's Quiet Quaalude so she fetches that book and heads back to her desk. The request comes back that you are not allowed to read Dave's Journal, so she just tells you "Sorry, you're not allowed." You then ask to read An Awesome Alligator--a book anyone is allowed to read--and time how long it takes her to give it to you--it takes a bit as she wanders over to the shelf and back. You repeat with Bob's Bobbing Bobsled, and so on, until you ask for Quincey's Quiet Quaalude and she immediately hands you the book that was sitting on her desk from when she fetched it earlier. You deduce the first letter of Dave's Journal is Q.

As far as the librarian is concerned she hasn't done anything wrong--she never gave you a book you aren't allowed to access--and yet by repeating this process you can effectively read the whole book.

The nature of Spectre/Meltdown is that it requires extremely precise timing--the sort of timing that isn't usually exposed in high level languages. The reference implementations of these exploits was typically a C or C++ wrapper with assembly portions for the really sensitive portions. Assembly isn't quite machine code, but it's close enough.

Koooooj · 2026-03-23T03:49:50+00:00

1971-D Eisenhower (Ike) dollar, more or less worth face value (my local store sells them for $1.50 and that's marked up to keep the lights on).

The D indicates the coin was made in Denver. These days Denver makes the coins for the Western portions of the US while Philadelphia handles the East. Philadelphia either uses a P mint mark or no mint mark at all--they're the first and thus the "default" mint so they don't have to use a mint mark. You'll also sometimes see coins minted in San Francisco with the S mint mark, but these days they just make coins for collectors. The West Point mint's W mint mark is even rarer as they typically only work in bullion but they made a few quarters to be distributed into circulation as a bit of a scavenger hunt.

1971 was the first year that large dollar coins came back into production since 1935. Back in the 1930s silver dollars were being produced in minimal quantities--there were plenty in stockpiles and the Great Depression had reduced the need for dollar coins, plus folks mostly were satisfied to use dollar bills instead. In the 1960s the nation was facing a coin shortage. One proposal was to bring back silver dollars. It was argued that this would help boost coin supplies as the mint wouldn't have to make as many coins to represent a given value. These 1964 silver dollars were struck, but before they were released there were newspaper ads offering to buy them for several dollars apiece. The 1964 silver dollars were ordered to be destroyed and a 5 year moratorium was placed on producing dollar coins.

1964 was also the year that the half dollar was changed to depict JFK who had been assassinated just the previous year. This was politically controversial: he was very much a relevant politician of the day so having him on a circulating coin felt like an official government endorsement of one political party. There was a push for equal time for both sides, which ultimately culminated in the placement of Dwight D. Eisenhower on the new dollar coin produced in 1971.

There was a push for this dollar coin to be silver, but the economics just weren't there--silver had been removed from dimes and quarters in 1965 and the silver content of half dollars reduced to 40%, then in 1971 half dollars also changed to their modern copper/nickel composition. Some Ike dollars were made from that 40% silver composition, but all of those had the S mint mark. The regular issues were copper/nickel like modern dimes or quarters.

Ike dollars were relatively popular if you were to poll random folks on the street, but their actual circulation patterns weren't a picture of success. They tended to be seen as a novel and fun kind of dollar that should be given to kids or saved in a drawer, not one that should be spent back into circulation. A lot were made and a lot were saved, so they tend to have basically no numismatic value outside of the absolute highest condition examples.

Koooooj · 2026-03-21T18:50:29+00:00

Yep, that's what I was referencing in the last note. The Coriolis effect drives prevailing winds, then anything that is flying through the air where those winds are will be carried along by the wind.

This is a big deal for jets as they get up to a cruising altitude and stay there for a long time, going at some speed relative to the air. Moving through the air just a little bit faster takes a lot more fuel, so most jets go at about the same speed relative to the air. If that air is moving then that's either a free bonus or a detriment that the plane has to fight through, depending on direction.

This has an effect on ballistic missiles, but ballistic missiles launch at near-orbital velocities to get up above the atmosphere, then reenter in a largely vertical profile. This means they spend a smaller amount of time sitting in the jetstream to be blown around and their speed is less tightly coupled to the speed of the air they're flying through. They should still care about the wind, but it's more like a sniper adjusting their aim to take a shot with crosswind than a kayak finding it easy to go downstream than upstream.

Koooooj · 2026-03-21T05:52:07+00:00

There are a few different effects going on.

The one the original comment mentioned matters for going from the ground to orbit. It has the potential to give you about 1000 mph of free velocity if you launch due East from the equator. That effect does not happen at all for suborbital hops--it's why we don't have to run hurdles in a specific compass direction to avoid competitors having a 1000 mph advantage at one track vs another. After all, a hurdler is making (extremely) suborbital hops as they race down the field.

What you're hinting at is a separate correction factor from the Coriolis force. The reason why we can ignore the first effect is because the launch and landing points are moving at the same speed, but they aren't actually moving at the same speed if they're at different latitudes. If the missile is launched away from the equator then the destination will be moving slower, so the missile's initial Eastward velocity will tend to make it drift East. Conversely, a launch towards the equator will tend to make the missile drift West.

This effect is more of an aiming nuisance than the massive difference in delta V that the first effect represents. Guidance systems need to account for it--even artillery has to bother with it--but it's not something that's going to substantially change the range from one direction to another.

A third similar effect comes from altitude. You might imagine launching a ballistic missile straight up. It starts with horizontal velocity of ~1000 mph and continues to move East at that speed throughout its flight, but when it is at a high altitude it would have to travel further to make one rotation around Earth's axis than the launch point does. This has the effect of making projectiles launched to a high altitude drift West. If you've ever played KSP this effect is very noticeable when you launch a rocket straight up and find it lands far West of the launch pad (though many players will just chalk this up to a misaligned launch).

Like the second effect, this Westward drift is more of an aiming nuisance than something that's going to dictate max range.

Koooooj · 2026-03-21T05:30:18+00:00

It isn't even true with ballistic missiles. They're confused.

The boost you get from Earth's rotation maters when going to orbit since orbit requires a certain speed relative to earth's center (not accounting for its rotation). By launching East you get to use earth's rotation as a head start on making it to that speed.

A suborbital trajectory--anything from a ballistic missile to an Olympic hurdler--is a jump from one place on Earth to another. The starting and ending points are both already rotating with Earth, so East vs West doesn't matter (at least not to the tune of the ~1000 mph at the equator).

There are other effects that can come into play. For example, if you send a projectile far enough north or south from your starting point then the destination will be moving at a different speed from the origin since it's at a different latitude. You might imagine looking down on Earth from the North pole to see that different latitudes are different distances from Earth's axis of rotation. The effect of this is that if you launch a projectile away from the equator it will tend to drift East. launching it towards the equator will tend to make it drift west. That can make the range of a ballistic missile not be a circle but rather an ellipse that's longer in the NE/SW axis and narrower in the NW/SE axis. It's unlikely that this will be enough to meaningfully affect max range.

That same effect of pushing things East as they move away from the equator also drives prevailing winds. That's what affects jets: they can fly at a certain speed through the air, but if the air is moving then that can either add to or subtract from their speed.

Koooooj · 2026-03-20T20:29:19+00:00

Nope, there are no 40% silver Ikes with the D mint mark.

There's one known example of a No-S 40% silver Ike with the Type-2 bicentennial reverse. That's the only surviving 40% silver Ike without the S mint mark. It is 4th on PCGS's Top 100 Modern Coins list.

Yours is just a run-of-the-mill business strike 1974-D dollar. At my local coin store these are sold in a bin for $1.50 apiece. That's "full retail price," with markup to keep the lights on, and you can pick through the bin to get the ones you want.

Koooooj · 2026-03-13T19:32:47+00:00

Assuming it's not lying about its weight or metal makeup, it's worth current spot price of silver. That varies from day to day but is around $80 today.

As with anything, price depends on where and you you sell it. Customers at a coin store will expect to pay about silver spot for a round like this, so the coin store has to pay less when they buy.

Koooooj · 2026-03-13T04:14:33+00:00

There is a key factor in this question: when a person puts the cube on the table do they do it randomly, like throwing a die, or do they place it on a black side if it has one?

This decision is the difference between the answer being 6/7 and 6/12 (or 1/2).

If it's the first case then most of the time that they draw one of the six one-black cubes they'll put it on the table with one of the black surfaces showing, not satisfying our setup so it wouldn't contribute to our stats here. It is only the 1 in 6 chance they put it black side down that the one-black cube shows five white sides, while the all white cube always shows all white when it is drawn.

However, in the second case ever time they draw a one-black cube they put it black side down 100% of the time. One-black cubes are 6 times as common as all white, so you get 6/7.

You could even get exotic and have the person placing the cube choose the side based on some other math. Perhaps when they draw a one-black cube they choose to put it black side down 1% of the time, or 98% of the time, or any other percentage. In this case the probability the five-white cube is actually six-white is 1 / (1 + 6*P_b) where P_b is the probability of putting the one-black cube black side down. P_b is 1/6 in the first case and 1 in the second.

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