Rotation with a twist

kenhills

kenhills

Joined
Dec 17, 2007
Messages
984
OK, so I have been throwing for 40 years but stopped on and off for 38 of them.
About 3 weeks ago I started up again and the "feel" is starting to come back. Being able to place my self up and back some from two fixed distances, 9 and 18 feet, which stick most of the time. I'm guessing one rotation at 9 feet and 2 at 18. I throw 3 different knives the first is a 8.5 " Gil Hibben the second a 8" throwing knife I made years ago and the last is a 12" Cold Steel something or other (distance changes with this one) with a para cord wrap. The Hibben I like the most, throw it, it rotates and sticks sharp edge down. The second knife which I throw form the same distance as the Hibben always seems to stick side ways meaning the blade edge is parallel to the ground. The cold steel generally sticks with the edge facing up. I am pretty damn sure that I am releasing the knives the same way yet they rotate differently and consistently. Any one got an explanation for it or a suggestion as to how to correct it.
 
I have no specific idea, but I find the result damn curious.

Of course, part of me is tempted to say "If they're sticking, don't worry too much."

But the physics on this are intriguing. Is there anything on your release that's catching...like a knot on the paracord wrap grazing your thumb? Something has to be adding roll to the throw.

All things being equal, your knife should be self-stabilizing to some extent and tumble along its more efficient face--the side, as you'd expect. But clearly there's a roll being added.

It would be interesting if you could tape your throw with a camcorder, and then slow down the playback to see if you can identify where in your throw the blade changes its orientation.

Anyone else have any ideas? This is new.
 
As far as I can tell nothing is catching. The two smaller knives while different in shape and weight both have smooth handles so there is nothing to catch on. The para cord wrapped handle could be but if it is I cant tell and it would be very slight. Also the cold steel knife is rather heavy and I would expect it to be a lot less prone to be effected by a slight graze. I will try to get someone to video the throw and try to post it.
 
I'm guessing one rotation at 9 feet and 2 at 18.
Click to expand...
well, actually the knife flies about 6 feet out of 9 because 3 feet is the length of your arm, so it should be closer to 15 feet for double rotation
 
My CS True Flight does something similar. Thrown by the handle it sticks with the same orientation as it is thrown. Thrown from the blade it sticks with the edge orientation reversed, every single time. If I throw it edge down from the blade, it sticks edge up. If I throw it edge up, it sticks edge down.
 
CaptInsano said:
My CS True Flight does something similar. Thrown by the handle it sticks with the same orientation as it is thrown. Thrown from the blade it sticks with the edge orientation reversed, every single time. If I throw it edge down from the blade, it sticks edge up. If I throw it edge up, it sticks edge down.
Click to expand...

Yeah, but does it stick to the side? I think that's the mystery that Kenhills is describing. Somehow it also rolls 90 degrees as well as spin!
 
Correct in order for the knife to land edge up when thrown from the handle (edge down) it will also have to rotate in another plane as well. I have often wondered when using a tape measure do you use the front or the back or for that matter the middle of the mark?
 
Knives (or any other object for that matter) will twist while flipping if they are asymmetrical in mass. If you took High School physics, you might remember the experiment where two wheels were rolled down a ramp, one with the mass evenly distributed and one with the mass focused around the edge. The one with the mass nearest the edge tended to resist changes in motion and thus rolled more slowly down the ramp.

The concept is called Moment of Inertia and there's a good demo here: http://www.youtube.com/watch?v=7mxV6f5nuJY if you're interested. Knowing this, if one side of a knife has a different moment of inertia than the other, it will tend to twist as it flips. You can observe this by flipping a hammer (or tomahawk) in your hands. Start with the head/blade parallel to the ground and flip it once and the head/blade will be reversed.

J-
 
I don't think that would explain why a single knife behaves differently when thrown from opposite ends, or why my tomahawk does not reverse the direction it is facing when thrown or flipped.
 
i wouldn't worry too much about the roll.... unless of course it worries your female model on the plywood board;)
 
the only thing i can think of is your relese is different try and throw in slow motion and watch your self throw ya now stance,grip and relese you must be doing something different if that dont work try and re-ballence your knife just my 2cents
 
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