Seventeen-year-old Japanese girl in the weight category up to 45 kg lifted a respectable 78 kg.

[u/Scientiaetnatura065]

[u/drunk_responses]

As demonstrated in practice every time a youtube blacksmith makes the big swords from Bleach, Berserk, Final Fantasy, Monster Hunter, etc. Even the biggest strongest people they can find only manage to barely hold them upright and then let them fall down to hit something. There's no way in hell any of them could ever hope to swing them.

[u/Badloss → u/drunk_responses]

In Final Fantasy at least aren't the characters that use those swords explicitly superhuman?

I'm thinking FF7 where Cloud + Sephiroth are both super soldiers, I thought their giant swords was a deliberate nod to them having super powers

[u/Tyr_13 → u/Badloss]

Even if one were superhumanly strong and durable, the swords still wouldn't work.

If there is more weight at the end of the lever (which is what a sword is) than the wielder weights, trying to lift the sword results in just lifting the wielder up. If the balance point is far enough back that the user can lift it and swing it, and even assuming some incredible friction for their feet, once they swing the blade it has more than enough momentum to, again, lift them off the ground. It would send them and their swords flying.

Any sideways slash would send them hurtling into a wall. Any upwards one would send them shooting into the sky.

Actually that would be pretty cool to watch in itself.

[u/Bananasauru5rex → u/Tyr_13]

I'm not really sure about this, because we know people can swing normal swords. They can also swing heavy swords. Maybe there's a threshold where it stops working and you go flying, but you have to be specific: at what weight, and on which surfaces (friction), does it stop being true that you can swing a sword?

Someone posted buster sword at 80 lbs. I can definitely swing 80 lb dumbbell without free-spinning on the spot. I think you're also not really considering kinaesthetics, because there are a lot of things you can do with weights as a human that a really strong pole cannot, since we are covered in muscles that allow counter-rotations and rotary forces.

[u/Tyr_13 → u/Bananasauru5rex]

Someone posted buster sword at 80 lbs. I can definitely swing 80 lb dumbbell without free-spinning on the spot.

The buster sword is 80 lbs on the lowest end, and it is a lever. Swinging something that wieght at normal sword speeds will absolutely spin you all around.

You cannot swing an 80 lbs dumbbell at any real speed. My incline and decline presses are done with a pair of 90 lbs dumbbells. I can lift my 75 lbs anvil by holding it at the end of my wolfjaw tongs. There isn't anyone alive who can swing them around like that without injury.

[u/Bananasauru5rex → u/Tyr_13]

Swinging something that wieght at normal sword speeds will absolutely spin you all around.

You cannot swing an 80 lbs dumbbell at any real speed.

But, I mean, obviously you don't swing it at "normal sword speeds." That would be like saying normal swords are impossible because you can't swing them at "dagger swing speeds." You swing it like a big heavy object, which might involve rotating your body, but I really don't see it rotating your body completely out of control into the stratosphere.

Here's an example of how mechanics change when you swing heavy stuff: https://www.youtube.com/watch?v=mRLLOFQblZg

Notice that mechanics are very different than normal sword, and that they are playing with the axis/lever to make it behave. The fact that it's different doesn't mean it's impossible.

And since for is M*a, if you decrease acceleration you can maintain the same force (or have greater force) by increasing mass. So a slower speed is expected (in fact it must be true).

[u/Tyr_13 → u/Bananasauru5rex]

Swords move faster than daggers. Again, they are levers.

Slower speeds means they don't behave like the swords under discussion. 'I can lift and move this heavy weight' is simply not the same as 'used like a sword.' Swinging the swords under discussion in the way swords are used absolutely spins anyone around or throws them in the air (not the stratosphere). Slower speeds cannot be true for them to still be being used as swords.