the behavior of rotating objects

murphy4trees

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AKA The Dzhanibekov Effect or Tennis Racket Theorem

thought you and Spidy might be interested in this short of thing
 
That was pretty cool Daniel, thanks. That's weird, I noticed that with the racket-ball racket when I was a little kid, but I just thought that I was unwittingly imparting a tiny spin on the thing that was making it flip.
 
And in all actuality, we still really don't know shit.

I bet the ancient Sumerians thought they were on top of it all!

:/:
 
And so I guess it would be practically impossible to have such spinning objects so well balanced that they wouldn't flip when spinning.
 
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  • #9
It makes you wonder how that might affect a falling top. I've had them spin 180 degrees on the way down, sot he notch was pointing straight up... Have thought about experimenting with it to to get it down to a reliable technique and then use it when there is an offending branch on one side of a tree that will catch something on the way down or won't clear an object on the ground
 
If you were to suspend a load on the line (piece of log) to maintain tension while falling, and put a wrap on the pull-line to induce a spin, like with a choker to spin a log, you might get it to spin, with a strong hinge on one side of the face cut and a dutchman on the other... dunno.

Seems like a tool for when you want to clear a to-be-removed branch below you, but don't absolutely have-to.
 
The thing about tops, Murph, like a limb, is they are reactive to wind resistance. The side with the most resistance always turns the work around. Well, from high enough it works out that way. Despite the vast amount of variables it is predictable.
 
So, maybe rotating an object in a vacuum might help prevent the flip. A top, being balanced as mentioned in the video, around it's normal axis of rotation will not do the flipping thing by design.
 
Given gravity and all, in a vacuum there would be no wind resistance to turn the work, it would fall faster and never orientate itself towards the direction of fall. Interesting thought.
 
like this...

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That was one of the craziest things I've ever seen. I still remember when that happened!!
 
Never seen that before, though had seen stuff about it on the TV.

Great how they had Joe Kittenger involved as well.
 
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  • #23
This is the top that spun 189 degrees on the way down. While I love Gerry's teaching on wind resistance and think that would be a good subject for videos, if you are trying to spin a top, wind is more something to overcome that use to your advantage.

I've given a lot of thought to this spin of this top and tried to put all the factors together.

Early separation is a must. VERY narrow face, and then as Sean mentioned a torque from the pull line and a hinge set up to hold on one side. Not sure which plays more of a factor (which is a very important distinction), the hinge or the pull, but it makes sense that you need to have a pull that continues after the piece starts to move. Usually, the pull line cannot keep up with the speed of a moving top. So you'd need a line that's set fairly low (COG or below) and a moving truck to get much torque.

I AM guessing the timber fallers will adjust their cuts to allow a tree to spin after it brushes another tree. Probably more just by using a narrow Humboldt than having the notch hold on one side.

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SO many factors to dial in. It seems more of an academic inquiry, than something that has much practical use in the field. But still this is the stuff I think about in bed.

13:21 the notch is pointing straight up

Just took another look.. the hinge was tapered. 3.5" on the wide side... 2" on the thin side, so that makes sense.
 
Sometimes, you just have to hold your mouth just right and give it a little English with a little coaxing push......
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