Sliding weights

[Jens Nordlunde]

Hi Fearn

Thanks for the mail, and yes I did forsee that I most likely would miss some important pieces of information, so let me try again.

Weight 250 g.
Length of blade 90 cm, impact 60 cm down the blade.
Length of sliding 60 cm. Starting 15 cm from the hilt.
Speed of impact 40 km/h
We must assume, not to make it too complicated, that the blade is straight, that the weight is in one piece sliding in the middle of the blade (double edged), and that the friction at any time is close to nil, although you are right that while fighting blod would slow the slider down.
I will comment on what you write about the beads, steel balls later on this thread.

Jens

[Jeff D]

Hi Jens,

As always you ask a interesting question. The purpose of a sliding weight (if it is indeed functional not decorative) is to move your point of balance down the blade. Essentialy converting a rapier (light blade with a point of balance closer to the hilt) into an axe. As you know the cutting ability has a lot of variables such as edge geometry, draw cut etc. However the sliding weights function would be to add mass to the point of impact thus increasing the kinetic energy which then gets converted into cutting energy. KE=1/2mv2 (kinetic energy = one half mass times the velocity squarded). The amount of mass added will then depend on where your sliding weight is in relation to the point of impact which ideally will be on the point of impact.

As a disclaimer I am not a physicist
Jeff

[Jens Nordlunde]

Hi Jeff,

Thanks for the kind words.
Would the effect not be bigger when, like I have done, let the glider pass the point of impact with a few cm?
My idea with this thread is not to get an exact answer, but to get an idea of, how much extra power a gliding weight did/could add to the sword.
I will comment on you quertion, 'The purpose of a sliding weight (if it is indeed functional not decorative) is to move your point of balance down the blade.' later, as I find this very interesting.

Jens

[Jeff D]

Originally Posted by Jens Nordlunde

Would the effect not be bigger when, like I have done, let the glider pass the point of impact with a few cm?

Hi Jens

Yes, the effect should be increased as there is a rotational kinetic energy that should increase directly proportional to the distance past the point of impact squared (I=mr2).

Jeff

[Jens Nordlunde]

Hi Jeff,

I don't understand the formula, but I am relieved to say that I do understand what you write, and I find this interesting.
Now, if the blade was twice as long, and the glider could glide twice as long, but the point of impact would be the same - what then?

Jens

[fearn]

This is definitely a neat problem.

Just thinking about it, I'd break the contribution of the weights into two categories.

1) changing the centers of gravity and percussion. The best way to think of this is as a sliding weight that can be fixed in place. Fix it at the bottom of the slide, and the sword acts more as a back-weighted stabbing weapon. Fix the weight forward, and the sword acts better as a forward-weighted chopping weapon.

2) the sliding weight acts to increase the impact force by some amount. This gets weird. For instance, the weights could add a second impact to a stab. You use the blade to stab forward, and once the blade slams to a halt, the weights slide forward and add a second thump.

Conversely, when sliding, the weights move in an arc (potentially a straight line) out, from resting near the hilt to the outer end of the slide as the blade moves. Again, they add some force at the end of the slide, but it is at an angle to the cut. This might or might not be a good thing.

In both cases, there's a notable jerk or twitch when the sliding weight hits hits either end of the slide. This might or might not be a good thing.

The nice thing is that this would be relatively easy to dummy up. Put ball bearings (or whatever) in a closed pipe of the length of the slide, and attach this pipe to a practice blade (perhaps with duct tape? ). Some empirical experimentation would be informative, I think.

Fearn

[Jens Nordlunde]

Hi Fearn,

Your observations are very good. When I thought of the problem, before I started the thread, I wondered what the maximum weight of the glider might have been, if you did not want to loose your sword - torne from you hand by the force of the glider.
You write, 'In both cases, there's a notable jerk or twitch when the sliding weight hits hits either end of the slide. This might or might not be a good thing.' Yes there would have been, and if this jerk is too hard I don't think it is any good for the user, nor for the sword - therfor the slider must not be too heavy - but heavy enough to give the wanted effect. How heavy it that?

Jens

[Rick]

Wouldn't that be measured by a formula of the distance traveled by the weight , the mass of the weight and the speed of the swing ?
The important variable being the speed of the swing ?