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This answer got me thinking about the concept of a weapon that was hard to start moving, hard to stop moving, but stayed fluid whilst moving.

I can't seem to find any lightweight melee weapons that behave as described, and after reading the comments and doing some research, the gyroscopic effect mentioned in the answer doesn't seem to actually work that way.

How can we make a lightweight weapon that behaves as described? In addition, if the answer to this question is "No it's not possible", please explain why in excruciating detail.

  • You don't need to worry about what this weapon will have to cut/strike/break etc. It only needs to move as described.

  • Don't worry about how the use of this weapon would be ineffective compared to other weapons.

  • Near-Future tech is okay as long as you can explain the theory behind it all.

Edit: Preferably, this weapon should be rigid.

Edit 2: For clarification, in case you don't want to read the comments, this weapon shouldn't be able to do an instantaneous 180 degree change in direction while maintaining its velocity. Instead, in order to do a 180 degree change in direction, the weapon would have to essentially make a "U" shape.

Edit 4: It seems that there is some confusion as to how well this weapon needs to be able to change directions. It doesn't have to be able to change directions quickly at all, and definitely not mid-swing. In order to change direction, the user may have to bring the weapon in a full circle around him (eg: do a spin).

For example: If the user started with a downwards overhead strike, the follow through would bring the weapon to the bottom right side, where he could potentially spin to the right and bring the weapon back around as a horizontal left to right side swipe.

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  • $\begingroup$ Really heavy weapons come to mind, I don't think that's what you're looking for but it's definitely easier to move a hammer when it's already moving. $\endgroup$ – DaaaahWhoosh May 20 '15 at 16:08
  • $\begingroup$ @DaaaahWhoosh Yes, that came to mind too, which is why I noted in my question that I couldn't find any lightweight weapons. I'm also asking specifically for a lightweight weapon. $\endgroup$ – Aify May 20 '15 at 16:09
  • $\begingroup$ Gyroscopic motion would make heavy weapons more balanced. Kind of like this. $\endgroup$ – Samuel May 20 '15 at 16:09
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    $\begingroup$ @Aify Ok. You want a high momentum with a low mass weapon. $\endgroup$ – Samuel May 20 '15 at 16:46
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    $\begingroup$ @Samuel: Not sure why I never considered the physics of those before. Amazing that they're actually even less useful than I thought they would be - I always just assumed they would be pointless for engineering/structural reasons. $\endgroup$ – Dan Smolinske May 21 '15 at 14:36
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What you describe is not possible.

You want a high momentum (hard to start, hard to stop) and low mass weapon. That's fine, but high momentum means you can't easily change its direction.

Momentum is $\vec p = m\vec v$, it's just the mass times the velocity vector. That means it's based on the direction and speed the weapon is moving and its mass.

If you want to change the direction of the weapon you can't just use the momentum for one direction and move it to another. You can add momentum or remove it by applying force for any particular direction. You can't use the momentum for one direction and change it to another direction.

If such a thing were possible a car could make a 60 mph U-turn and end up moving in the opposite direction. Or a warrior with a battle hammer could make a U-turn mid-strike and correct a missed blow.

You're trying to build an inertia-less drive weapon. You'll have to turn off the inertial negation right before impact, otherwise the weapon will accept the change in direction without doing any damage.


Inspired by Ville Niemi's answer I remembered seeing this video. It still doesn't break inertia like you want, but by adding a pressure-sensitive grid to the grip of a small mace outfitted with rocket boosters the control of the weapon could be greatly assisted. Think of it as computer controlled stabilization thrusters with the input being your grip on the weapon.

Again, this only allows the user to have high momentum strikes with rocket assisted maneuvering. It does not inherently meet the requirements of what you asked for because that would break physics.

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  • $\begingroup$ I think this goes a bit too much into the extremes - I'm not saying that the weapon has to be able do a small U Turn mid strike quickly in order to correct a missed blow or whatnot at all. Even if the weapon has to make a U turn it should have to be a large U turn. $\endgroup$ – Aify May 20 '15 at 18:03
  • $\begingroup$ @Aify Yes, a large U-turn is fine, but a large U-turn requires at least twice the energy as stopping the weapon. There is no case where a large U-turn will be easier than stopping the weapon. If you're not asking for that then all you're asking for is a normal lightweight weapon. $\endgroup$ – Samuel May 20 '15 at 18:06
  • $\begingroup$ I'm probably understanding the physics wrong, but shouldn't guiding the weapon to do a large U turn take LESS energy than stopping the weapon? $\endgroup$ – Aify May 20 '15 at 18:19
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    $\begingroup$ Actually, your answer is a little off the mark. Cars and planes are routinely U turning with very little energy and effort. The effect is called aerodynamics. Wings can deflect air around them to generate large forces tangential to the direction of motion. Thus momentum is conserved (roughly speaking). $\endgroup$ – Aron May 20 '15 at 19:34
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    $\begingroup$ @Samuel wow. You completely misread my comment. Gravity is an example of a conservative force field which allows objects to continuously change direction without expending energy. In order to do so, you can either manipulate a force field, in which the object will move... Or just manipulate the Higgs field directly and forget Newtonian physics entirely. $\endgroup$ – Aron May 21 '15 at 10:54
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So you want a relatively light weapon that is hard to get moving, hard to stop moving, but pretty easy to keep moving.

I'd suggest a flail.

Flails are not so much hard to start moving as they are hard to get going. You can't just swing a flail if you want to use it effectively, you have to get it spinning around. That way, you can increase the end's angular momentum, which works just as well as regular momentum when it bashes into the enemy's skull.

As for stopping the flail, there's two options: either hit it into something (preferably something you're not too fond of), or stop applying forces to it and let air resistance slow it down for you. Just like starting up, this process isn't nearly as quick as it would be for something like a sword.

As for moving the flail once it's in motion, it may take some practice (and some bruises), but once you've mastered the flail you can make full use of its angular momentum to swing it anywhere.

Now, for your lightweight component, the flail can be pretty much as lightweight as you want it to be. I don't have the math to back this up, but I imagine just increasing the length of the chain/rope would impart more momentum to the end, meaning a sufficiently big flail need not be very heavy to match the power of a shorter, heavier flail.

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  • $\begingroup$ Wouldn't that just make it a whip? I should probably state that it should be a rigid weapon.... $\endgroup$ – Aify May 20 '15 at 16:41
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    $\begingroup$ @Aify yeah, you should probably have stated that. However, I think you could still get a fair level of rigidity with a flail-like weapon. For instance, nunchucks operate on similar physics, and are pretty good at blocking things. $\endgroup$ – DaaaahWhoosh May 20 '15 at 16:43
  • $\begingroup$ I've put it in as an edit so that your answer is still valid. Where nunchuks fails this is that it's not hard to get it moving. A flick of the wrist is all it takes. $\endgroup$ – Aify May 20 '15 at 16:49
  • $\begingroup$ @Aify while I would say it's a bit harder than that, I agree nunchucks aren't the best example. But what about a three-section staff? $\endgroup$ – DaaaahWhoosh May 20 '15 at 17:05
  • $\begingroup$ 3 section staffs also aren't that hard to start moving. I've used both nunchucks and 3 section staffs before, and once you know the proper motions... well, they don't classify as "hard to start moving and hard to stop". $\endgroup$ – Aify May 20 '15 at 17:08
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Perhaps it may be more effective to take a different look at the problem. Let's look at why you'd want a weapon that demands fluidity.

Consider what we are trying to maximize. The answer you reference specifies "hard to start moving, hard to stop moving, but stayed fluid whilst moving." Now, if you really think about this, all three of those are really negative traits. Hard to start moving means you can't respond very fast. Hard to stop moving means if you miss, its hard to recover without losing control of your weapon. Staying fluid while moving really says "weapon doesn't respond to every stimulus you could want to give it." That set of criteria is actually quite an undesirable set of weapon characteristics.

So let's look at the heavy weight example: a mace. Let's pick a heavy one, so that we have all of the characteristics desired. It's slow to start, slow to stop, and generally you try to keep it moving to keep control of its inertia. So why would anyone want this? When it comes to heavy weight weapons, the answer is easy: power. If its slow for you to stop, its hard for the opponent to stop it also. Once the mace is in action, the opponent most move out of the way, or take substantial effort to deflect/block it.

But if we want a light weight weapon that is hard for us to stop, what do we get for it? There are many Chinese weapons which are light weight and require absolute fluidity of movement. They all stem from the same goal: the weapons provide control in subtle ways. Consider a Kung Fu Sword. I swing my sword at you, and you block it. If the sword is lightweight, it bends and keeps going a fair distance beyond the block. The sword tip may even point at your face (scary!). If only there was a way to keep striking.

As a matter of fact, there is. Kung Fu does not teach that the strike ends when the block occurs. The block is simply a melding of the two swords for a moment. There is still a pointy bit that is moving towards their face. If you can keep control of that pointy bit, it doesn't matter if they blocked you or not. You can continue to strike.

The trick, of course, is that you need to stay connected wit the tip of your weapon, and that's what the fluidity is for. Even during something as violent as a steel on steel collision, you want to maintain control of you weapon. The Chinese approach to this (and the approach of many Asian arts of war) is that the sword is not treated as its own thing. It is an integrated part of your body. Thus they care as much about the position of your shoulder blades as you swing as they do your wrists, even thought the wrists have such an obvious effect on the direction the blade is pointing. When your opponent blocks, they try to disrupt the movement of your body/sword. If you can refuse to let them disrupt you, your attack moves through their block.

So what does this mean? Look for weapons which give some benefit in exchange for their strict rules. As an excellent example, lets look at the Chinese dart, which is not a melee weapon, but is an interesting test case. The dart's fearsome power is its ability to change directions rapidly. The practitioner is constantly adjusting the length of the dart's chain, and it is often very hard for an opponent to predict exactly how the dart can move because of this.

However, fluidity is essential. If a motion is not fluid, it puts a kink in the chain which flows outward to the dart, disrupting your control. You basically lose control of the dart when you aren't fluid, making it dangerous to absolutely everyone within reach. Unfortunately, while your opponent can step out of reach, you must be in the middle. Failure to be fluid often causes the dart to hurt yourself!

So a near-future nanotech solution? I'm going to redefine rigid to mean it is not exactly pliant to your will. Let's make a nanotech sword which can change shape to wrap around an opponents defenses. However, defensive techniques catch up. People quickly learned a particular defensive pattern which involved getting close enough to the hilt to confuse the nanoparticles (which are not very bright) into thinking their commands were as valid as the original wielder's. At this point, they take the sword over, and kill the owner.

The solution is a ferocious beast: the living sword. It's quiescent state is that of a plain dull grey sword, showing no special properties. However, as the fight begins, it begins to bring its own "mind" into the fight, trying to accomplish whatever it thinks is right. To stop the defensive move that worked against the earlier evolution, the sword does not respond to your will instantaneously. It responds slower, making certain that the only input it really listens to comes from the wielder (because they can hold onto it the longest). If it detects the discord which naturally occurs from two masters trying to control it, it immediately snaps forward back into a dull grey sword and waits for the outcome.

This also serves as a safeguard. The nanamachines are scary. They'll do very unsightly things if left unchecked. Accordingly, they are programmed to only act like they are alive if they can detect the will of a human guiding them. The easiest way to give them that signal is to give one fluid motion that lets them see your entire body is integrated.

The result would also create a line of martial arts masters who allow this communication to work both ways. While the normal wielder simply tells the sword what to do, these masters also listen to the feedback from the nanomachines, and are willing to adjust their own positioning or stance to better suit the nanomachines. This allows the masters to unlock their full potential. While anyone can make a sword do what they want over time, a master can make the sword do what they want almost instantly, because they are so integrated that the sword knows it's still connected to a masterful human. It doens't have to worry about mixed signals.

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  • $\begingroup$ Very interesting approach. You've got my +1. $\endgroup$ – Aify May 21 '15 at 19:51
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Rocket hammer. It needs long arcs for the rocket to accelerate it into full speed and has no reverse thrusters so you can't just stop it. I think it would more realistically use a rocket-ramjet such as used by many missiles and have some thrust vectoring to make turning it less stressful on your arms.

The rocket hammer is not really that light, but you should be able to build a sword or something with similar active thrust system.

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  • $\begingroup$ Related: ixionsagadt.wikia.com/wiki/Kon_Hokaze $\endgroup$ – Aify May 20 '15 at 17:23
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    $\begingroup$ Doesn't really sound like it would be that 'fluid' mid-swing. It would be just as hard to change direction as it would be to start it moving. $\endgroup$ – DaaaahWhoosh May 20 '15 at 17:27
  • $\begingroup$ @DaaaahWhoosh Yeah, you'd really need that thrust vectoring I suggested. The idea here it that since the power comes from the rocket, not the mass of the weapon, the way the weapon behaves can be tuned by changing the rocket controls. No idea how realistic it would be or how it would actually work. $\endgroup$ – Ville Niemi May 20 '15 at 19:33
  • $\begingroup$ This idea reminded me of a rocket powered hovering drone video I saw once. I've edited it into my answer and cited you. $\endgroup$ – Samuel May 20 '15 at 19:54
  • $\begingroup$ @Samuel Yes, as you say, you can't break inertia, but with rocket power and some software, you could fake it. I think that is the closest you can get. $\endgroup$ – Ville Niemi May 20 '15 at 20:00
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Various sorts of chain or rope type weapons exist, from whips to various sorts of flails to a Japanese weapon which used a weighted chain on the end of a short sickle to entrap an enemy sword so you cold close in for the killing blow.

There is also an Indian weapon which is essentially a "whip-sword", a thin piece of razor sharp metal which can be employed much like a whip to slash targets.

The parameters of the question are a bit odd, though. Anyone with a weapon which is difficult to start in motion will be at a grave disadvantage against someone with a much lighter, easier to manipulate weapon. Large weapons which were difficult to manipulate were generally only used in very special circumstances, such as pole arms to knock or pull a knight from his horse, pikes used in dense formations or huge two handed swords used to attack fully armoured men or break into pike formations. There are other examples, but you will find most were also specialized for particular tasks and generally for particular times and places.

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  • $\begingroup$ Note that in the second bullet point of the question I had already stated not to worry about how useless this weapon would be compared to other weapons. All I care about is how I can make this weapon, not it's effectiveness :P $\endgroup$ – Aify May 20 '15 at 18:36
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if you're after a rigid weapon... well anything of a weight that won't unbalance the wielder technically would work.

flexible weapons however include things like rope darts and meteor hammers. they're tricky to get going(not a ton of strength is required but plenty of skill), and don't really stop unless they hit something hard enough to stop them, and are extremely fast and controllable.

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Something like a shaolin spade might fit the bill.
A long weapon with a cutting head on one end could be very fluid/graceful in motion, but if it is unbalanced, and heavier on the sharp part, then starting and stopping it gracefully could be much more difficult.

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