science question for fantasy novel:

If a sword fell from around cloud height and hit a boulder-sized rock in the middle fo a forest, what would happen?

how far away would this be noticeable, either because of sound or vision?

what condition would the area where it landed be in?

this bears on the beginning of my book.

How much does the sword weigh?

Which cloud height are you talking about? Different clouds live at different heights.

What kind of boulder? Granite? Limestone?

hmm... i knew this would get tricky...

well, i didn't expect an easy answer. if someone knows the best way to leanr this stuff...

the variables can be adjusted as neccessary.

the result i'd like is- the sword survives, the angels on a nearby cloud notice this event, come to investigate, and the hero draws the sword form the stone. i don't need the stone to be truly intact, but i'd prefer something more than a pile of dust. some incidental damage is acceptable, but this isn't noticed by the world at large. luckily, the forest is on the edge of civlization.

the weight of the sword: I haven't entirely decided what type of sword it is. it will be used in two hands, but it's definitely not a claymore or a katana, the only types of two-handed swords that immediately come to mind. it's definitely sharp, unlike a claymore, and is light enough to be moved relatively quickly and skillfully.

of course, the wielder is an angel who is 7 feet tall and is very strong by human standards, so you never know.

I haven't read up on clouds yet- the angels use enchanted clouds for transportation, and the major characters are keeping a watch from the clouds. the magic clouds are intended to blend in with real clouds though. the should be close enough to the ground to see what goes on, but they have vision like hakws so that can be fairly high.

the sword which is dropped can be any height sufficient so that they would notice it, either in falling (resembling a shooting star? especially if it magically glows?) or on impact (explosion? clanging sound? sonic boom? [if magically accelerated])

the sword is being dropped by a villain who wants them to notice and investigate, and in particular to take the sword for themselves.

the boulder can be of any convenient stone that would be found in a european forest. i have the humans speaking a pidgin-german (or possbily something scandinavian- i haven't worked much with the humans yet) and i figured a german climate would make sense.

Re: hmm... i knew this would get tricky...

Okay.

Let's say the angels ride above strato-culumus clouds. That gives you a height of 6,500 feet, mebbe.

Let's say the weight of the sword is 4 lbs, just to be on the large side.

If you have an Earth-like gravity, the sword will fall at 32 ft per second per second (to simplify). According to my rough calculations, it will take 8 seconds to fall that far, and it will hit the boulder at 2,048 feet per second.

Ouch. Let's say aerodynamics encourages the sword to fall point downward. The tip of that sword will strike with

KE=1/2M * V(squared)

So the kinetic energy would be half four lbs times 2,048 squared. Or 8,388,608 lbs/fpss

Let's pretend you wanted to compare that to a two thousand lb car. By my (probably flawed) calculations, that car would have to be driving just over 91.6 feet per second when it hit to have an equal force. That's about 62 mph.

Let's pretend you took a lot of useless mass from the back of hte car, the roof, the radio, whatever, and built a sword-like spar on the front of it, along with the structure that could hold the car's frame solid. Then let's pretend you rammed that spar by remote control into a rock at 62.5 whatever mph.

How would that look? How would that sound?

Not the same, I'm sure. But it could be close.

I'm not that good at this stuff. Maybe someone can step in and correct me.

Re: hmm... i knew this would get tricky...

Um...:wha

I'm not about to analyze your calcs, HConn; they look good enough. I think your judgement of aerodynamics of the sword is correct; the air resistance of the hilt would cause it to follow the point. But you have 4 tons of kinetic energy applied by the point of the sword (negligible area) to the rock.

It seems to me there'd be a rather LOUD thunk, followed by virtual anihilation of the rock, followed by the sword buried up to, if not beyond, its hilt in the soil beneath the rock. I doubt there would be any 'clanging' of metal, as you might expect, if say, the sword were to be swung into the rock by the 7'-tall angel.

Re: hmm... i knew this would get tricky...

well, I suppose i don't need the sword to be in the stone. it was only for mythical allusions.

the sword sinking into the ground is fine with me.

how far away would the thunk be audible? (this si one of the more important details.)

what condidition would the area around the impact be in? would there be a shockwave?

Re: hmm... i knew this would get tricky...

Wow, HConn....

:: walks away muttering something incoherent about abismal physics classes ::

Re: hmm... i knew this would get tricky...

how far away would the thunk be audible?

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Based on HConn's physics, which I have no quarrel with, I'd think you'd hear the 'thunk' about as far away as you'd hear a car crash--maybe a quarter to a half mile--unless it happened in an acoustically enhanced area, such as a canyon or a vast empty plain. Such things as trees, grasses, or other 'soft' and irregular items will absorb the sound, diminishing the distance it travels. If your sword fell into a forest, I doubt the sound of its crash into the rock would be heard more than a few hundred yards away.

As to the condition of the surrounding area after the crash, again it would depend on what was there. In a forest, ree trunks would be scarred, with bits of the rock imbedded in the bark. On a rocky plain, there would be a small crater (small, being not more than a meter in diameter), with pieces of the destroyed rock scattered as far as a hundred meters away. Maybe. We could ask HConn to work out the physics, but I think it's not that important. The sword isn't massive enough or travelling fast enough to cause the kind of devastation that a meteor would.

Re: hmm... i knew this would get tricky...

Pitching in as a not-a-scientist (I write fantasy rather than SF) all I can add to that is that, if the people hearing are angels, you could assume that their hearing is more acute than that of humans, so I don't think the carrying-distance of the sound would be a major problem.

Re: hmm... i knew this would get tricky...

Flawed, there are so many variables for the sound you shouldn't worry about it.

Also, I'd have your character pull the sword out of a shattered oak tree.

Maca, I had terrible high school physics classes. Guys were doing bong hits in the back of the room while the teacher nattered on, oblivious. Google did all my thinking for me.

BTW, on another thread I recommended that everyone writing sf/f subscribe to SFWA's Bulletin. Every issue, Robert Metzger writes a State of the Art column that does a grownup version of what I did. The latest column was about gadgets. Previous columns were about melting the polar ice to create "Waterworld" or creating a system where humans could draw all of their calories from sunlight.

Cool, cool stuff.

Re: hmm... i knew this would get tricky...

Guys were doing bong hits in the back of the room while the teacher nattered on oblivious.

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:lol That sounds really familiar, HConn.

Re: hmm... i knew this would get tricky...

Sounds like a less dangerous version of the guy in my science class who one fine day opened up the gas valve for the bunsen burners and lit it so that a jet of flame shot across the aisle.

:ack

It's amazing he didn't blow the top floor off our high school and us with it.

Re: hmm... i knew this would get tricky...

We had those gas jet nozzles, too, but the administration was smart enough to cut off the gas. Otherwise, we would have been closing the class with gas scares every period.

We did have a guy who set fire to his own shirt, though. On purpose. He was bored and laying a lighter flame on the sleeve of his flannel shirt, then beating it out. After about a dozen times, one of the fires got out of control.

Re: hmm... i knew this would get tricky...

In high school chemistry lab, after a demonstration on how elemental sodium reacts with water, one kid stole the lump of sodium (about the size of a tennis ball), took it still wrapped in its oily paper toweling to the restrooms and flushed it.

About a half-hour later, they shut down the school to repair the plumbing.

chem..

Sounds like a less dangerous version of the guy in my science class who one fine day opened up the gas valve for the bunsen burners and lit it so that a jet of flame shot across the aisle.

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Funny you should say that. I just got back from chem lab about 15 minutes ago and did that exact same thing myself. Whoops.

You'd think us college kids would learn. :smack

PS - Chunk, what is it with me and fire??

falling

Generally speaking, a sword that falls from the clouds will be falling no faster than a sword that falls from 100 feet. Atmospheric resistance stops an object from accelerating once terminal velocity has been reached. For most objects, terminal velocity is only 220 miles per hour.

If the planet had no atmosphere, the velocity would increase of a per second per sceond basis until the planet stopped its fall, but it simply doesn't work this way on any planet with an atmosphere.


It's like a bullet. Fire a bullet straight up and it may leave the barrel at 4,000 feet per second and reach an altitude of four miles. But when it falls back down it will be traveling only as fast as atmospheric resistance will let it.

So your sword falling from the clouds will only be traveling about 220 mph when it hits, no matter how much it weighs. (Assuming it isn't a mile long.) The atmosphere slows metal down, too. A meteor weigh a thousand times as much as any sword may enter the atmosphere at 14,000 mph, but by the time it reachs the ground it's seldom traveling faster than 300 mph.

So even if your sword was thrown from Mars, it still isn't going to be going very fast when it hits the ground.

Re: falling

I couldn't find any information on terminal velocity for something as heavy as a sword, so I ignored it.

But I'm sure James is right.

terminal velocity

Terminal velocity affects anything of any weight. It will, of course, affect a feather far more than a lump of steel, but even metal slows trememendously. An aerodynamic shape lessens the stopping power of the atmosphere, but not by a very great deal. Even if the sword falls point down, it will still max out at under 500mph, under the best of circumstances, and probably won't pass 300.

Aerodynamics will help an object retain velocity, but a falling sword starts out at zero velocity, so there's nothing to maintain.

Swords are heavy. Most who hold one for the first time can't believe how much some weigh. They range from three pounds to more than twenty pounds.

But if it weren't for the ability of the atmosphere to drastically slow down how fast a heavy object falls, we wouldn't need to build bombs. A 200 pound chunk of metal falling at 32 feet per second per second from 20 miles would have more explosive force than a bomb.

Re: terminal velocity

wouldn't, say a granite rock, react differently than a softer stone such as sand stone. :shrug I don't know anything about physics past basic motion physics.

I think having it fall into a tree would give it less of a King Aurthur kind of feel (unless that's what your going for) and since it's angels your dealing with sound definitely does not matter.

Re: terminal velocity

yes, i *am* going for a King Arthur feel.
more specifically, i'm pointing out the absurdity of the King Arthur myth. the belief of the person who finds it that it's a sign from heaven that he is the savior is misguided.

i don't belive in chosen kings, and i don't think magic swords have anything to do with it.

Re: terminal velocity

But if it weren't for the ability of the atmosphere to drastically slow down how fast a heavy object falls, we wouldn't need to build bombs. A 200 pound chunk of metal falling at 32 feet per second per second from 20 miles would have more explosive force than a bomb.

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A good example of using "thrown" objects as a weapon is The Moon is a Harsh Mistress by R. A. Heinlein. In it, rocks were lobbed at Earth from the Moon, and had more devasting effects than nuclear weapons. Of course, there, it was an issue of mass coupled with velocity. If your angel threw the sword to the ground instead of just dropping it, there is potential for greater destruction upon impact. But James' point about terminal velocity is something to consider.

However, for the purposes of the story, have the sword do what you want it to. If you need major destruction, have your angel hurl the sword to the ground. Only the true pedants will worry that you've violated any laws of physics.

Re: terminal velocity

There's a widespread theory that the sword in the stone actually derives from a Bronze Age ritual where the young prince pulled his sword out of the stone mould it was cast in. Which would mean that it was his status that caused the ritual, not the other way round.

Re: terminal velocity

That's really interesting. Thanks, Nyki.

Re: terminal velocity

Oooh, Nyki... :jump

Tidbits like that put my brain into overdrive. Thanks.

mass

Mass is an important consideration, not so much because of velocity as because of inertia. Would you rather be struck by a ping pong ball traveling 300 mph, or a car traveling 50mph? Of course, mass and velocity together make for a wicked combination. But the faster something strikes the atmosphere, the more impact the atmosphere has on it. The atnmosphere works much like water. If you dive into the water from ten feet, the impact isn't much. Hit the water traveling 220mph, however, and it's like slamming into concrete. Air works pretty much the same way.

But if something has enough mass, it doesn't have to strike the ground very fast to release a lot of energy. Inertia does the job just fine.

But I wouldn't take the King Arthur myth too seriously. It's a parable, and contains some extrmely valuable lessons. Mostly, it's just a very good story with some very good characters.

And, of course, the Bible says God chooses all leaders, the good, the bad, the wicked, the foolish, all for His own purpose. So Biblically speaking, all kings and all leaders are chosen by God.

Be that as it may, true, false, of indifferent, if I find a stone buried in rock, and if no one else can move it, and I somehow manage it, trust me, I will think something special is going on. I'm not dumb enough to think I'm stronger than a bunch of young men with Conan biceps. That was the thing with King Arthur. It wasn't that he could pull the sword from the stone, it was that no one else could, including grown many with several times his strength. That sort of blows the mold theory, too.

But I wouldn't try faking the science of terminal velocity. Even most high school kids will bust you on this one. It's too basic. For that matter, neglect atmospheric resistance, and I doubt there's an editor in the world you could get the manuscript past.