Physics question from sci-fi/fantasy novel

IronWing

No Lifer
Jul 20, 2001
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In Gene Wolfe's The Shadow of the Torturer, part one of The Book of the New Sun, the protagonist gets a headsman's sword that has a mercury filled core. The idea is that as the sword is raised the mercury rests in the pummel or at least at the pommel end of the blade and that as the sword is brought down, the mercury flows to the tip thus increasing the force of the blow.

I'm thinking that the mercury would be moving radially, perpendicular to the direction of impact, and not provide any increase in blow force but tend to pull the sword out of the hand of the headsman. What sayeth ATOT?

Also, if you haven't read Gene Wolfe's The Book of the New Sun, I highly recommend the books.
 
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Anubis

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Aug 31, 2001
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tbqhwy.com
im not sure what mercury weighs in that volume but as you swing the sword it will all be pushed to the top/tip of the sword, which would increase its weight which would increase its angular momentum as it was swung, resulting in more applied force

how much is a matter of some simple math which im too lazy to do
 

lxskllr

No Lifer
Nov 30, 2004
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I think you're generally right. It would slightly increase blow force at the expense of unpredictability. Imo, shifting weight isn't a desireable feature in a striking/cutting tool.
 

cbrunny

Diamond Member
Oct 12, 2007
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It would be cooler if the sword had a rocket strapped to the tip that went off when the sword was being swung.

Not a physicist, but the movement of the mercury would increase the mass of the tip part.

Imagine a baseball bat that is completely hollow, and fill it with a litre of water. Swing it around and you can imagine the water sloshing to the end of the bat. If you were to hit someone with that bat, regardless of the direction the bat was swung the water would flow to the end of the bat and the increased mass would cause a more forceful impact. The only way this would do more damage than a completely solid bat is if the hollow bat can be swung so much harder as a result of the decreased weight than a completely solid bat. How much harder? No idea. I don't even know how to begin trying to solve that one. But I imagine it would have to be swung REALLY hard in order to pass the impact force of a solid bat.

So, I call shenanigans.
 

GagHalfrunt

Lifer
Apr 19, 2001
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Imagine a baseball bat that is completely hollow, and fill it with a litre of water. Swing it around and you can imagine the water sloshing to the end of the bat. If you were to hit someone with that bat, regardless of the direction the bat was swung the water would flow to the end of the bat and the increased mass would cause a more forceful impact. The only way this would do more damage than a completely solid bat is if the hollow bat can be swung so much harder as a result of the decreased weight than a completely solid bat. How much harder? No idea. I don't even know how to begin trying to solve that one. But I imagine it would have to be swung REALLY hard in order to pass the impact force of a solid bat.

You don't have to imagine it, the liquid bat actually existed. Spalding sold a softball bat called The Wave (or the Tidal Wave maybe??) in the 80's and there were patents filed for liquid-filled golf clubs from that era too. I can't imagine it working, at least in golf or baseball where control of the swing is important.

In practice there were real swords filled with ball bearings from hundreds of years earlier. Same thing although somewhat more practical than liquid as leaks would not have been a problem. They were rare and not widely copied, that leads me to believe that they didn't work all that well.
 

gururu2

Senior member
Oct 14, 2007
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If you fill a sock with rocks and keep the rocks near your hand. the sock will not hurt anyone. If you put the rocks at the end of the sock it will hurt a lot.
 

ImpulsE69

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Jan 8, 2010
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Wouldn't the mercury (due to momentum force of the sword) not exert its own force until the sword came to a stop and due to momentum of the mercury 'hitting' the tip? If you swing something fast enough, liquid stays (for the most part) at the back, not the front. It only comes front when the item stops.

Or is the core completely full? In which case it has no movement anyway. I would assume the point is it has an air bubble so the liquid can move.
 

glenn1

Lifer
Sep 6, 2000
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Seems like you would lose overall mass of the blade by the empty space of the chamber the mercury was held. And the small amount of mercury involved probably wouldn't impart much additional momentum anyway I would think, are a couple fluid ounces of mercury shifting inside a blade really going to make that much difference?
 
Feb 4, 2009
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Seems like you would lose overall mass of the blade by the empty space of the chamber the mercury was held. And the small amount of mercury involved probably wouldn't impart much additional momentum anyway I would think, are a couple fluid ounces of mercury shifting inside a blade really going to make that much difference?

and a hollow sword would probably be pretty fragile. I'd prefer to have a solid one that won't bend/break.
 

DigDog

Lifer
Jun 3, 2011
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^ what he said.
also, mercury would be in the tip pretty much always, as you swing your sword constantly. combat is about more than just a single swing.

stupid fantasy gimmick is stupid.
 

Anubis

No Lifer
Aug 31, 2001
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You don't have to imagine it, the liquid bat actually existed. Spalding sold a softball bat called The Wave (or the Tidal Wave maybe??) in the 80's and there were patents filed for liquid-filled golf clubs from that era too. I can't imagine it working, at least in golf or baseball where control of the swing is important.

In practice there were real swords filled with ball bearings from hundreds of years earlier. Same thing although somewhat more practical than liquid as leaks would not have been a problem. They were rare and not widely copied, that leads me to believe that they didn't work all that well.

im pretty sure I had that bat back when I was a kid, I remember it
 

IronWing

No Lifer
Jul 20, 2001
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^ what he said.
also, mercury would be in the tip pretty much always, as you swing your sword constantly. combat is about more than just a single swing.

stupid fantasy gimmick is stupid.

It's an executioner's sword. One swing does it all.
 
Feb 25, 2011
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Only works if the mercury is denser than whatever the rest of the sword is made out of.

Inserting a tungsten core at the tip would be better (it's denser than mercury) and give the weapon more predictable handling characteristics. (It's not moving around on you.)

But a weapon like that, with its center of gravity that far from the handle, would definitely be harder and more fatiguing to work with. And since F=(1/2)(m)(v^2) it'd be better in most circumstances to have a lighter weapon (steel) with a center of gravity closer to the hilt, that you could swing faster.
 
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Schmide

Diamond Member
Mar 7, 2002
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Moreover if one mass was moving with a quasi linear motion (mercury) and the other in a angular motion (metal), the collision as the mercury hits the tip would be tangential to the force you wish to inflict on ones opponent. It would be like the Jai alai xistera throw.

Now if you were highly skilled you could use this effect to improve your stabbing motion but not your angular slicing motion.
 

Joepublic2

Golden Member
Jan 22, 2005
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Wouldn't the mercury (due to momentum force of the sword) not exert its own force until the sword came to a stop and due to momentum of the mercury 'hitting' the tip? If you swing something fast enough, liquid stays (for the most part) at the back, not the front. It only comes front when the item stops.

Or is the core completely full? In which case it has no movement anyway. I would assume the point is it has an air bubble so the liquid can move.

Depends on how fast the sword is swung, the arc it travels, etc. A better idea would be to have an internal mass, say enriched uranium (extremely dense) that's moved up and down the interior of the blade by some mechanism that's intelligently controlled by the user, a program, or some combination of the two. Then if you were losing you could put the sword into self destruct mode and an explosive charge would fire, propelling the enriched uranium into a smaller mass of uranium/neutron source in the other end and have it explode as a gun-type fission bomb.

Silly book, better to use a blaster instead.

Yeah. Or this.
 
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