How to Spot a Psychopath

A reader writes:

Why is "black powder" gray when I make it, but black when I buy it?

I live in the Land of the Free and the Home of the Well-Regulated Militia and can buy gunpowder over the counter to, uh, use in my collection of historic muzzle-loading muskets, Officer. The stuff you buy, though (and the stuff I've seen on Mythbusters too, actually) is sort of shiny black, in various different particle sizes depending on burn rate and whatnot.

But when I MADE gunpowder as a kid, the recipe was three-quarters saltpeter, and saltpeter looks like salt. It's white. So the powder comes out pale gray.

What gives?

Steven

As you say, the recipe for standard black powder for firearms is 75% potassium nitrate, 15% charcoal and 10% sulfur, by weight. And this does indeed create a grey powder, not a black one. Everything associated with making and combusting black powder tends to end up pretty darn black, thanks to the charcoal in the mix and the copious smoke and other solid residue created by the powder's inefficient combustion, but the powder itself isn't black.

Commercial black powder looks black because the little lumps of the stuff are coated with graphite. In the manufacturing process, the powder's mixed with water or some other liquid binder, pressed into cakes and dried, then crushed and screened into powders of various particle size, larger particles producing a slower burn. The graphite serves no chemical purpose, but it lubricates the particles, and also makes the bulk powder electrically conductive enough that it's unlikely to initiate proceedings unexpectedly because of a static-electricity spark.

(You can't, by the way, make decent black powder using graphite, or any other high-purity carbon, in place of charcoal, because the leftover wood impurities in charcoal make it ignite at a lower temperature. Pure carbon makes a black powder that burns slowly; it might eventually push a bullet out of a rifle's muzzle.)

Black powder remains a somewhat excitable substance, even with graphite on it; it is, for instance, still pretty impact-sensitive, if not by the standards of substances of which only lunatics prepare more than a gram.

It's now apparently becoming harder to find black powder even in the gun-happiest parts of the USA; instead, there are various black-powder substitutes. All of the substitutes are safer than black powder, and many of them have other benefits, like not fouling your muzzle-loader with corrosive sulfur compounds.

Psycho Science, as I have brilliantly decided to call it, is a new regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

A reader writes:

How is it possible that I can belay my husband when rock climbing? He is almost twice my weight.

At our local climbing gym, the top of the "cliff" has a cylinder, which the climbing rope is thrown over, wrapped around, and falls down off the other side (i.e., it's touching 540° of the cylinder). The employees say that it works because the rope is wrapped around the cylinder twice. I'd like a more scientific explanation, though: does wrapping it actually increase the amount I can lift? Is it just friction?

As another data point, I belayed him once on an incorrectly-set-up wall where the rope was only thrown over the cylinder, not wrapped around it. I felt alarmingly weightless when supporting my husband's weight, but my feet stayed on the ground.

Kristina

Yes, belaying really is pretty much all about friction.

When you wrap a rope around an object a few times and pull on both ends, there's enormous friction between the rope and the object, even if the object's smooth. If the tension on one end of the rope, plus the friction, exceeds the tension on the other end, nothing moves (the exact numbers can be calculated using the "capstan equation"). So you can belay your husband. Actually, with enough turns around the cylinder and assuming the cylinder and the rope are strong enough, you could belay anything at all. (Getting a grand piano, a garbage truck, the USS Nimitz or the planet Mercury into the climbing gym is left as an exercise for the reader.)

When either end of the line is slack, which is the case most of the time, almost all of the friction disappears and it's easy for the climber to proceed upward while the belayer takes up the slack.

What you can't do, of course, is actually lift whatever's on the other end of the belaying line. Trying to do that puts you on the wrong end of the equation; you'd have to pull with a force greater than the mass on the other end of the line, plus the friction, which gets worse the harder you pull. In this situation, with a few turns around the cylinder, the world's strongest man would be unable to hoist a small child. If you add another, movable smooth cylinder, though, or preferably an actual pulley, you can make a block and tackle and lift arbitrarily large loads by applying a smaller force over a longer distance.

Standard yachting capstans (the things that you are apparently legally required to see people frantically cranking whenever TV news reports on a yacht race) are pretty interesting, too. They contain a planetary gearset that only operates when the capstan's being turned in one direction. Turn the capstan crank that way, and the gearset turns the outer barrel of the capstan at a fraction of the speed at which you turn the crank, making it possible to apply a strong pull to a line under tension. Turn the capstan the other way, though, and the gears lock up and connect the barrel directly to the crank, allowing you to let the rope out again quickly.

(Well, that's the way the old one depicted in one of my favourite toilet books worked, anyway. I'm sure there are now also capstans that can turn the barrel faster than the crank. They probably have infinitely variable transmissions in them by now.)

Psycho Science, as I have brilliantly decided to call it, is a new regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

A reader writes:

Is it possible to spin an object with two axes of rotation from just one initial impulse?

Specifically the question is about spinning a cricket ball.

If we take the X axis to be running between the wickets, Y to be the other horizontal axis, and Z to be vertical; spin bowlers generally spin the ball on a single axis somewhere between X and Y, depending on whether it's a break or a top-spinner. But, would it not also be possible to spin the ball simultaneously on the X and Z axes, so that it would be virtually impossible to tell which way the ball will turn until it lands? It would start off spinning on Z and X, but as it rotates about the Z axis the other axis of rotation would change.

I've been attempting to do this but it does not seem to work. The ball only seems to take one axis. I'm wondering if it's not actually possible to do it with just one spin, and it would require an initial spin followed by a separate impact?

James

Not only is it not possible to spin an object with two axes of rotation from just one initial impulse, but it's not possible for a rigid body to revolve simultaneously about more than one axis, at all, per Euler's rotation theorem. If a rigid body is spinning around an axis you call X, and you apply a force to it that, were it motionless, would cause it to start spinning around an axis you call Y that's at right angles to X, you'll end up with it spinning about some single axis between the two, the axis and speed of rotation being determined by the forces that've acted on the object.

An ongoing force acting on a rigid object, though, can cause an ongoing change in its axis of rotation. The axis will always pass through the object's centre of gravity, but it can be moved around in numerous ways.

In the case of a cricket ball, the axis of rotation can change slowly as a result of aerodynamic forces - which can also push the ball off the perfect ballistic trajectory it'd have if there were no air - and suddenly when the ball bounces off the ground, as it usually does in cricket.

(In an interesting piece of US/Commonwealth parallel evolution, cricket balls and baseballs are actually extremely similar in size, mass and construction. Apart from colour, the principal difference between the two is that a cricket ball has "equator" stitching while a baseball is made from two saddle-shaped pieces of leather, and the cricket ball has a harder surface. Cricket balls are also generally bowled somewhat slower than baseballs are pitched, and lose some momentum when they bounce off the ground. This lamentable reduction in lethal potential is, thankfully, largely compensated for by the cricket ball's harder surface and the bowler's ability to bounce it right up into the batsman's chin at ninety miles an hour.)

There are many other situations in which a spinning object can appear to have more than one axis of rotation, but they're all the result of forces acting on the object. A flying ball experiences aerodynamic forces, a billiard ball skids across the table with a spin different from its direction of travel, a comet is pushed around by gas from its own melting ice, a gyroscope precesses because of the pull of gravity, the wobble ("nutation") of the Earth's axis is the result of tidal forces from the moon and sun, and so on.

Regarding your own bowling experiments: Sorry, but you cannae change the laws o' physics. Even if you cheat, the ball's still only going to have one axis of rotation at a time, and that axis is only going to change in response to aerodynamics and hitting the ground.

Psycho Science, as I have brilliantly decided to call it, is a new regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

A reader writes:

I was flying at night from Chicago, IL to Cleveland, OH. It was a very cool but humid night. Since this was a short flight (1:10) we were in a fairly low altitude commuter jet. There are a lot of small towns between the cities separated by nothing much. It was a clear night and we were of course well above the sparse clouds. They were sparse, that is, until we flew over a town; a short way into the town a low overcast began.

Looking down on it, you could see the street and street lights as you began to cross the town, and the thickening, low-lying overcast, enough to obscure everything, until you reached the town edge, after which it thinned out and disappeared shortly before you reached the actual edge of the town, if you see what I mean. If the town was a disc, the overcast would be a somewhat smaller diameter disc centered and overlaying it.

We also flew over several football fields with their field lights on. By the lights, there was a cloud. Away from them, say by the middle of the field, the cloud stopped.

It was weird and after making this hop more times than I can count I've never seen it before. I'm sure it was a function of the cool temperatures (low 40s), high humidity and the local warming from the lights and from the cities themselves. But I can't think of a mechanism.

Mike

Clouds often form over towns, as a side-effect of the urban heat island effect.

Towns are usually warmer than the surrounding countryside, because we make our towns out of substances like brick and asphalt, which absorb and retain solar heat better than grass and trees. Because the towns are warmer, the air above them tends to be warmer and thus less dense than the air around the town. So the air over the town rises, and air around the town is sucked in to replace it, whereupon that air warms up and rises too. It's sort of like the fire-bombing of Dresden except, you know, less horrifying.

(The urban heat island effect is a favourite of climate-change deniers, who allege that rising temperature readings over the years are explained by those readings being taken in places which genuinely are getting hotter, but only because they contain more and more buildings and roads. These higher temperatures do not, the argument goes, therefore indicate any actual overall climate change. The claim that the world's climatologists wouldn't have noticed and compensated for this phenomenon is, to my mind, about as plausible as the creationist allegation that paleontologists don't know that carbon dating doesn't work on things that are millions of years old.)

The warm air rising over a town will cool down as it rises and mixes with the rest of the atmosphere, and the cooler air is, the less water vapour it can hold. If the air over the town was humid - which it often is over Chicago and Cleveland, since they're each on the shore of a huge lake - then clouds will form as the rising air cools and water condenses out.

I think the particularly striking effect you saw was the result of the local weather being just right to give a textbook demonstration of the heat-island-clouds effect, even around small heat sources like floodlights.

Pollution from towns may also encourage cloud formation, because soot and other particulates can serve as nuclei for atmospheric water vapour to condense onto. This phenomenon is used in agriculture to prevent the formation of frost; oil-fired "smudge pots" burning with a nice dirty smoky flame don't actually greatly warm the orchards they're sitting in, but they do produce lots of nice little particles for water to condense onto, and then drift away. This reduces the amount of water that condenses on the trees and, later, freezes.

Making clouds in this way is quite easy; making rain in some particular place is a lot harder.

(Note, by the way, that clouds are not made of water vapour. Water vapour is a gas, and invisible. The clouds you see in the sky, and the visible "steam" from your kettle, are tiny particles of liquid water. This also means that visible "steam" at normal atmospheric pressure can't be any hotter than 100°C. True, invisible, steam can be much, much hotter than this. You can get a nasty burn from the visible "steam" that appears some distance from, say, an open stopcock on the side of an old locomotive, especially if you're close enough to the nozzle that there's still some actual vapour in there. But the invisible "live steam" closer to the nozzle can, quite literally, flay the flesh from your bones.)

Psycho Science, as I have brilliantly decided to call it, is a new regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

A reader writes:

Here's an interesting science question (for me at least!).

I've often observed a phenomenon. In sunlight - especially early or late when the sun is low and the rays come low - you can play with shadows on fairly distant objects (few meters); this seems essential for the effect.

The effect itself: If you move your fingers close to each other, while the sun shines through between them, as you close the gap between the fingers, the shadow of your fingers seem to stretch out and touch well before they actually touch. (Of course you don't have to use fingers, you can use something else.)

It's weird, really weird.

Steve

The sun isn't a point source of light; like most light sources, it has a clearly visible diameter. All shadows from it are, therefore, fuzzy to a greater or lesser extent, depending on how close the shadow-casting object is to the surface on which the shadow is cast.

A fuzzy shadow has an "umbra" and a "penumbra". The umbra is the evenly-dark portion of the shadow; if you're standing in the umbra, you can't see the light-source at all. The penumbra is the portion around the umbra which is partially shadowed. If you're standing in the penumbra, you can see some, but not all, of the light source's area. The closer you are to the umbra, the less of the light source you can see.

The umbra and penumbra distinction is particularly important if you're trying to get a good view of a solar eclipse; in a partial solar eclipse, the moon never covers the whole disc of the sun. You can see this in that famous picture of a solar-eclipse shadow viewed from low earth orbit, and it's diagrammed, rather less beautifully, here:

(Note also the "antumbra", which you see if you're far enough from the shadow-casting object that you see the light source all around it. This illustration's good, too. In a lunar eclipse, the moon is covered by the earth's shadow; a lunar eclipse is partial if the moon is never completely covered by the umbra of the earth-shadow.)

Now let's get back to the shadows of your fingers when you're doing Deformed Rabbit in late-afternoon sunshine. The shadow of each of your fingers, when it's cast by a light with considerable angular size like the sun or a much closer, much smaller light source like a light bulb, also has an umbra and a penumbra. Where two finger-shadow penumbrae overlap, an ant squinting up from the overlap area would see one side of the sun obscured by one of your fingers, and the other by another finger.

Result, a darker shadow, as the penumbrae add up. As you've noticed, this makes it look as if the shadows are stretching toward each other.

(You don't see this effect very much with most household lighting, because most people don't paint their rooms matte black and light them with a single dangling frosted bulb. Uneven illumination escaping from a lampshade, and indirect light bouncing off the ceiling, make normal indoor lighting quite unlike sunlight on a clear day, even if there's only one light source in the room.)

Freaky shadows can also be caused by diffraction effects, but with a wide light source and relatively large shadowing objects, you won't see them. If you've got a really really tiny light source with, preferably, a very tightly limited spectral output, though, all shadows will be super-sharp (with invisibly small penumbrae), and diffraction effects spring into visibility.

You can get such a light source if you unscrew the collimating lens completely from a laser diode module; this is possible with many, but not all, cheap laser pointers. Now you've got a narrow-spectrum light source about the size of a bacterium to play with!

Psycho Science, as I have brilliantly decided to call it, is a new regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

A reader writes:

You can get high on nutmeg. You really definitely can, it's not like smoking banana peels or gum leaves or something.

So why isn't nutmeg illegal?

F.

Yes, nutmeg is indeed a psychoactive drug. You need to eat a fair bit of the stuff, especially if it's not fresh, but it'll make the world look different all right.

Unfortunately for the hopeful supermarket trip-taker, though, being high on nutmeg is a rather unpleasant experience. The main active ingredient is "myristicin", which in the nutmeg plant serves to keep insects from eating it.

Like a number of other psychoactive compounds present in plants you can legally grow, myristicin is a "deliriant". It can cause pleasant effects - euphoria, interesting dreams while you're still awake - but it can also just stupefy and confuse the user, essentially giving you a preview of severe senile dementia. Effects of large doses of myristicin include headache, body pains, anxiety and vomiting, though usually not death. In this last respect myristicin is superior to the psychoactive compounds in other "legal" plants, like Echium plantagineum ("Paterson's Curse") and Datura stramonium ("jimson weed").

Myristicin also takes some hours to take effect, and can then last for a straight day before it even starts to wear off. The first quality results in overdoses, when after five hours of nothing much happening the user decides to knock back another bottle of nutmeg. The second can lock the user into a very lengthy tour of a place you'd much rather not be.

Psycho Science, as I have brilliantly decided to call it, is a new regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

A reader writes:

My brilliant son put a jar of mustard in the microwave for... a while. When we regained the ability to breathe and I managed to stop laughing, I grounded him because of his clear violation of the Chemical Weapons Convention, to which Australia is a signatory.

Then I started thinking. We just inhaled gaseous hot English mustard... does that mean we just inhaled mustard gas? Are we now at a higher risk of lung cancer, or something?

Caitlin

"Mustard", in culinary parlance, is a condiment made from mustard-plant seeds. Hot mustard is bad news if you get it in your eyes or sinuses, on account of a compound called allyl isothiocyanate, or AITC to its friends.

"Mustard", in chemical-weapons parlance, refers to any agent which creates a burning sensation and "lachrymatory" effect similar to that of AITC, and generally also has a somewhat similar smell to culinary mustard. These compounds are not at all related to edible mustard, though, and all have exciting extra toxic effects. The original "sulfur mustard" compounds that were used in World War I, for instance, are highly carcinogenic and cause agonising skin blisters and chemical burns, which can take as much as a day to develop.

It would be unwise of me to mention, in these pages which your son may read, that microwaving pepper can create a similar noxious cloud, the active agent in which is "piperine".

So I will not.

Psycho Science, as I have brilliantly decided to call it, is a new regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

A reader writes:

Why can't you see the bones in your finger/hand when you shine a bright light through it? Veins show up well, but bones are practically invisible. Are live bones as see-through as live flesh?

Ryan

Bones, alive or dead, are pretty much opaque to visible light. If your flesh were for some reason perfectly transparent but your bones stayed as they are, you'd be a lovely Ray Harryhausen walking skeleton. (Or, more accurately, a Fritz Leiber ghoul.)

Your flesh isn't transparent, though; it's translucent, and diffuses light that enters it. So instead of your hand-bones being as visible as a fish in an aquarium, they're as invisible as a fish that is for some reason attempting to survive in a tank full of milk.

If that fish in its milk-tank comes close to the side of the tank, you'll be able to see it, just as you can see the little dark veins that're close to the surface on the palm side of your fingers when you shine a flashlight through your hand. Just the few millimetres of flesh on either side of the bones, though, diffuses the light so much that it's hard to tell that there's a bone there at all.

Psycho Science, as I have brilliantly decided to call it, is a new regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.