| Topic: |
Science > Physics |
| User: |
"Sam the Bam" |
| Date: |
06 Nov 2006 08:40:22 PM |
| Object: |
nunchuck physics |
The nunchuck is a flail type weapon, common in Okinawan and
Chinese martial arts; 2 sticks, connected by a short length of
rope. Presumably everyone has seen one, sometime... if not
live, maybe a Kung Fu flick...
Watch a demo, the tip travels blindingly fast. My question is:
from a physics viewpoint, where does that speed come from?
I've been trying to model it, without success. I mean, we
know that the rim of a wheel moves faster than the hub - call
it 'radial velocity amplification' - but that doesn't explain the
chucks. The sticks are about a meter length, total, but if you
spun a one meter stick (gripping at one end), you wouldn't get
close to such speed. How does a 2" rope do the trick?
Take it as a schoolboy problem...
Sam
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| User: "Timo A. Nieminen" |
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| Title: Re: nunchuck physics |
07 Nov 2006 02:43:21 AM |
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On Tue, 6 Nov 2006, Sam the Bam wrote:
The nunchuck is a flail type weapon, common in Okinawan and
Chinese martial arts; 2 sticks, connected by a short length of
rope. Presumably everyone has seen one, sometime... if not
live, maybe a Kung Fu flick...
Watch a demo, the tip travels blindingly fast. My question is:
from a physics viewpoint, where does that speed come from?
I've been trying to model it, without success. I mean, we
know that the rim of a wheel moves faster than the hub - call
it 'radial velocity amplification' - but that doesn't explain the
chucks. The sticks are about a meter length, total, but if you
spun a one meter stick (gripping at one end), you wouldn't get
close to such speed. How does a 2" rope do the trick?
Part A: Swinging it around in a circle, many times:
The rope frees the non-held-onto half to move faster. If you're holding
onto a stick (ie you have your fingers and thumb wrapped around it), you
can only twirl it around as fast as you can turn your hand around.
Nunchucks free you from that limitation. Just tie a weight to the end of a
light rope, and swing it around as fast as you can, and it will go around
in much less time than it would take to swing a stick around in a circle.
Part B: Single swing:
You can do the same thing with a rigid stick, especially if it is weighted
so that the centre of mass is close to your hand (eg, a well-balanced
sword). Start with your hand holding the stick/sword just above your
shoulder, with the stick pointing backwards. Now strike forwards, trying
to minimise rotation of the stick (it will rotate a bit, but it won't be
rotating very quickly). When your arm is almost fully extended, stop
moving your hand forwards, and even pull it back if you can, and the stick
will whip around quickly. Nunchucks will do a similar thing, but even more
so. A simple way (but is it a correct way?) to explain it is that you
convert linear motion to circular motion by stopping the centre of
rotation from moving. You get a similar effect when you use a sling to
throw a stone in a single swing (which is the very best sling technique,
IMHO, if you value rate-of-fire [about 1 aimed shot every 5 seconds is
feasible, if you aim quickly]); the "radial velocity amplification" you
note above helps as well (and the same will also help with nunchucks). If
you do the long-range long-sling swing around many times in a horizontal
circle, then you're mainly using the Part A effect above.
Think about cracking a whip: how fast does the tip move, and why?
Nunchucks are about halfway between whips and rigid sticks!
--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
E-prints: http://eprint.uq.edu.au/view/person/Nieminen,_Timo_A..html
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html
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| User: "Sam the Bam" |
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| Title: Re: nunchuck physics |
07 Nov 2006 09:38:33 PM |
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Timo A. Nieminen wrote:
The nunchuck is a flail type weapon, common in Okinawan and
Chinese martial arts; 2 sticks, connected by a short length of
rope.
Watch a demo, the tip travels blindingly fast. My question is:
from a physics viewpoint, where does that speed come from?
I've been trying to model it, without success. I mean, we
know that the rim of a wheel moves faster than the hub - call
it 'radial velocity amplification' - but that doesn't explain the
chucks. The sticks are about a meter length, total, but if you
spun a one meter stick (gripping at one end), you wouldn't get
close to such speed. How does a 2" rope do the trick?
Part A: Swinging it around in a circle, many times:
The rope frees the non-held-onto half to move faster. If you're holding
onto a stick (ie you have your fingers and thumb wrapped around it), you
can only twirl it around as fast as you can turn your hand around...
Just tie a weight to the end of a
light rope, and swing it around as fast as you can, and it will go around
in much less time than it would take to swing a stick around in a circle.
Yes, that's obvious, but why? Just saying "it's free to
move faster" doesn't tell us where the extra speed
originates... my car is free to move faster than the throttle
position, but that never happens...
It's a schoolboy problem, and I've been out of school a long time...
Part B: Single swing:
You can do the same thing with a rigid stick, especially if it is weighted
so that the centre of mass is close to your hand (eg, a well-balanced
sword). Start with your hand holding the stick/sword just above your
shoulder, with the stick pointing backwards. Now strike forwards, trying
to minimise rotation of the stick (it will rotate a bit, but it won't be
rotating very quickly). When your arm is almost fully extended, stop
moving your hand forwards, and even pull it back if you can, and the stick
will whip around quickly.
It will actually accelerate? Color me skeptical... I call it an
illusion.
Nunchucks will do a similar thing, but even more
so. A simple way (but is it a correct way?) to explain it is that you
convert linear motion to circular motion by stopping the centre of
rotation from moving.
??
You get a similar effect when you use a sling to
throw a stone in a single swing; the "radial velocity
amplification" you note above helps as well
(and the same will also help with nunchucks). If
you do the long-range long-sling swing around many times in a horizontal
circle, then you're mainly using the Part A effect above.
Yes, but the original question remains: where
does the added velocity come from? We know it's
true, but I can't explain it in terms of Newtonian physics.
Think about cracking a whip: how fast does the tip move, and why?
Nunchucks are about halfway between whips and rigid sticks!
Which segues into my next question...
Sam
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| User: "Tom Sanderson" |
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| Title: Re: nunchuck physics |
08 Nov 2006 09:20:13 AM |
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"Sam the Bam" <samthebam1@lycos.com> wrote:
The nunchuck is a flail type weapon, common in Okinawan and
Chinese martial arts; 2 sticks, connected by a short length of
rope.
Watch a demo, the tip travels blindingly fast. My question is:
from a physics viewpoint, where does that speed come from?
F=ma. You have speed, therefore you have a, therefore you have F. The
force in question is the tension force in the rope connecting the two
handles. The rope constrains the motion of the free handle, forcing it into
a tight (fast) arc. That constraint puts tension in the rope, which pulls
on the fixed handle, which pulls on your hand. If you don't hold it
tightly, the nunchuck will fly out of your hand. If the rope breaks, it
won't whip around.
The speed comes from the kinematics of the nunchuck. The energy to get that
speed comes from the restraint force the user has to exert on the handle.
You can do the same thing with a rigid stick
<snip>
When your arm is almost fully extended, stop
moving your hand forwards, and even pull it back if you can, and the
stick
will whip around quickly.
It will actually accelerate? Color me skeptical... I call it an
illusion.
Things moving in non-straight tracks are, by definition, accelerating.
Tom.
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| User: "Timo Nieminen" |
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| Title: Re: nunchuck physics |
09 Nov 2006 05:56:52 PM |
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On Wed, 7 Nov 2006, Sam the Bam wrote:
Timo A. Nieminen wrote:
The nunchuck is a flail type weapon, common in Okinawan and
Chinese martial arts; 2 sticks, connected by a short length of
rope.
Watch a demo, the tip travels blindingly fast. My question is:
from a physics viewpoint, where does that speed come from?
I've been trying to model it, without success. I mean, we
know that the rim of a wheel moves faster than the hub - call
it 'radial velocity amplification' - but that doesn't explain the
chucks. The sticks are about a meter length, total, but if you
spun a one meter stick (gripping at one end), you wouldn't get
close to such speed. How does a 2" rope do the trick?
Part A: Swinging it around in a circle, many times:
The rope frees the non-held-onto half to move faster. If you're holding
onto a stick (ie you have your fingers and thumb wrapped around it), you
can only twirl it around as fast as you can turn your hand around...
Just tie a weight to the end of a
light rope, and swing it around as fast as you can, and it will go around
in much less time than it would take to swing a stick around in a circle.
Yes, that's obvious, but why? Just saying "it's free to
move faster" doesn't tell us where the extra speed
originates...
Tp make something move quickly, you need to provide kinetic energy. Work
done is force x distance, or torque x angle rotated through.
Take a brick, and see how far you can throw it. The range is approximately
proportional to v^2, so proportional to energy/mass. Take a baseball, and
see how far you can throw it. Compare the range vs energy/mass. Take a
marble, and do likewise. Finally, try a ball-bearing.
There's a limit to how fast you can move your hand. For throwing, the
limit applies to how fast you can move your hand forwards during the
throw. For twirling a stick, it depends on how fast you can turn you hand
in a circle. If, instead, you twirl a weight a string, you no longer need
to
It's a schoolboy problem, and I've been out of school a long time...
It isn't a schoolboy physics problem. It isn't basic physics - it's
biomechanics.
Part B: Single swing:
You can do the same thing with a rigid stick, especially if it is weighted
so that the centre of mass is close to your hand (eg, a well-balanced
sword). Start with your hand holding the stick/sword just above your
shoulder, with the stick pointing backwards. Now strike forwards, trying
to minimise rotation of the stick (it will rotate a bit, but it won't be
rotating very quickly). When your arm is almost fully extended, stop
moving your hand forwards, and even pull it back if you can, and the stick
will whip around quickly.
It will actually accelerate? Color me skeptical... I call it an
illusion.
Will the tip of the stick increase in speed? Perhaps, perhaps not - it
depends on where the centre of mass is compared to your grip. Try it
with a well-weighted stick.
Nunchucks will do a similar thing, but even more
so. A simple way (but is it a correct way?) to explain it is that you
convert linear motion to circular motion by stopping the centre of
rotation from moving.
??
With the stick (or better, something balanced like a sword, like a sword),
the point about which the rotation takes place is your grip. With
nunchucks, the rotation takes place about the point where the rope
attached to the part you're holding onto.
Angular momentum will be conserved. The exact details of what happens
depend on the balance of the nunchucks. Having the centre of mass closer
to the pivot point gives a larger increase in speed (and as a result,
makes the nunchucks harder to control, and isn't always desirable).
OK, let us do some maths for the simplest case: nunchuck moving forwards
at speed v1, with no rotation at all. The held half is stopped abruptly,
so the free half swings around. There will be a force applied on the free
half at the pivot point which will slow the foward motion of the centre of
mass of the free half, but as this force goes through the pivot point,
there is no torque about this point. Therefore, the angular momentum about
the pivot point will stay the same.
Let:
L = length of free half
L/2 = distance to centre of mass
v1 = initial speed
v2 = final speed of tip, which we are trying to find
m = mass of free half
I = moment of inertia of the free half, = mL^2/3 for rotation about one
end
w = angular speed, = v2/L
Initial angular momentum = linear momentum x L/2
= m v1 L / 2
Final angular momentum = I w
= m L^2 v2 / 3L = m L v2 / 3
Since this is equal to the initial angular momentum,
m L v2 / 3 = m v1 L / 2
v2 = 1.5 v1
so the tip moves faster. (The centre of mass moves slower, since its final
speed is v2/2 = 0.75 v1)
You get a similar effect when you use a sling to
throw a stone in a single swing; the "radial velocity
amplification" you note above helps as well
(and the same will also help with nunchucks). If
you do the long-range long-sling swing around many times in a horizontal
circle, then you're mainly using the Part A effect above.
Yes, but the original question remains: where
does the added velocity come from? We know it's
true, but I can't explain it in terms of Newtonian physics.
The example with the maths above is about as far as you can go with
Newtonian physics. Beyond that - and for the swing-around-many-times
problem, you're in biomechanics, which is rather harder than basic
Newtonian physics.
--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
E-prints: http://eprint.uq.edu.au/view/person/Nieminen,_Timo_A..html
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html
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| User: "tj Frazir" |
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| Title: Re: nunchuck physics |
08 Nov 2006 12:28:14 AM |
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radius was converted into speed from centifical into centripital force ,
radius was shortend and the centrifical force was conveted into speed.
You fucking dumbasses .
sam you fucking moron and uncle ***** al the jackass should learn some
physics.
There is only 1 corect answer STUPID FUCKS and you did not get it.
shame on you dumbasses
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| User: "Uncle Al" |
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| Title: Re: nunchuck physics |
07 Nov 2006 10:31:32 AM |
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Sam the Bam wrote:
The nunchuck is a flail type weapon, common in Okinawan and
Chinese martial arts; 2 sticks, connected by a short length of
rope. Presumably everyone has seen one, sometime... if not
live, maybe a Kung Fu flick...
Watch a demo, the tip travels blindingly fast. My question is:
from a physics viewpoint, where does that speed come from?
I've been trying to model it, without success. I mean, we
know that the rim of a wheel moves faster than the hub - call
it 'radial velocity amplification' - but that doesn't explain the
chucks. The sticks are about a meter length, total, but if you
spun a one meter stick (gripping at one end), you wouldn't get
close to such speed. How does a 2" rope do the trick?
Take it as a schoolboy problem...
Actually a British sailor problem. A nunchuck is a whip. The
connecting rope or chain is not a point pivot.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz3.pdf
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| User: "Sorcerer" |
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| Title: Re: nunchuck physics |
07 Nov 2006 10:51:22 AM |
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"Uncle Al" <UncleAl0@hate.spam.net> wrote in message
news:4550B4E4.A10FA9C4@hate.spam.net...
[snip river of *****]
FOaD
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| User: "Sam the Bam" |
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| Title: Re: nunchuck physics |
07 Nov 2006 09:44:28 PM |
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Sam the Bam wrote:
The nunchuck is a flail type weapon, common in Okinawan and
Chinese martial arts; 2 sticks, connected by a short length of
rope. Presumably everyone has seen one, sometime... if not
live, maybe a Kung Fu flick...
Watch a demo, the tip travels blindingly fast. My question is:
from a physics viewpoint, where does that speed come from?
I've been trying to model it, without success. I mean, we
know that the rim of a wheel moves faster than the hub - call
it 'radial velocity amplification' - but that doesn't explain the
chucks. The sticks are about a meter length, total, but if you
spun a one meter stick (gripping at one end), you wouldn't get
close to such speed. How does a 2" rope do the trick?
Actually a British sailor problem.
?
A nunchuck is a whip. The
connecting rope or chain is not a point pivot.
Two rigid rods, connected by a short rope?
I don't see the whip model, and I don't see
a nunchuck 'waving'...
However, that does lead me to ask: I have seen
reports that a whip's tip will move at near speed of
sound, when it 'cracks'. It's the same mystery as
my nunchuck question - how does that speed arise?
You can't explain it in terms of rotation and arm geometry...
Sam
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| User: "Tom Sanderson" |
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| Title: Re: nunchuck physics |
08 Nov 2006 09:23:56 AM |
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"Sam the Bam" <samthebam1@lycos.com> wrote
A nunchuck is a whip. The
connecting rope or chain is not a point pivot.
Two rigid rods, connected by a short rope?
I don't see the whip model, and I don't see a nunchuck 'waving'...
You're thinking too large. A whip is just a multi-segment nunchuck. If you
had a million tiny rigid segments tied together by a million tiny ropes, it
would look and act just like a whip.
I have seen
reports that a whip's tip will move at near speed of
sound, when it 'cracks'. It's the same mystery as
my nunchuck question - how does that speed arise?
It's just the kinetic energy of the whole whip motion being concenctrated in
to the whip tip. The energy comes from the user's arm...the rest of it is
just a fancy energy/motion converter that takes slow, large-displacement
motion of one end of the whip and concentrates it to very fast,
small-displacement motion at the end. Sort of a solid-state gearbox, if
that makes any sense.
You can't explain it in terms of rotation and arm geometry...
Of course not. A whip (and a nunchuck) isn't a rigid body.
Tom.
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| User: "Sam the Bam" |
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| Title: Re: nunchuck physics |
09 Nov 2006 02:03:05 PM |
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Tom Sanderson wrote:
A nunchuck is a whip. The
connecting rope or chain is not a point pivot.
Two rigid rods, connected by a short rope?
I don't see the whip model, and I don't see a nunchuck 'waving'...
You're thinking too large. A whip is just a multi-segment nunchuck. If you
had a million tiny rigid segments tied together by a million tiny ropes, it
would look and act just like a whip.
But you don't. You have 2 rods, with one rope.
The limit argument doesn't apply.
I have seen reports that a whip's tip will move at near
speed of sound, when it 'cracks'. It's the same mystery
as my nunchuck question - how does that speed arise?
It's just the kinetic energy of the whole whip motion being concenctrated in
to the whip tip. The energy comes from the user's arm...
That seems clear, but...
the rest of it is just a fancy energy/motion converter that
takes slow, large-displacement
motion of one end of the whip and concentrates it to very fast,
small-displacement motion at the end. Sort of a solid-state gearbox, if
that makes any sense.
It doesn't. The "concentration of energy" pseudo-explanation
simply begs the question.
Ditto the gearbox model - gear motion is simply explained,
refering to sprocket radii as moment arms; a wheel size ratio
2:1 produces linear velocity 2:1.
Sam
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| User: "Rich Grise" |
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| Title: Re: nunchuck physics |
10 Nov 2006 07:52:13 PM |
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On Thu, 09 Nov 2006 12:03:05 -0800, Sam the Bam wrote:
Tom Sanderson wrote:
A nunchuck is a whip. The
connecting rope or chain is not a point pivot.
Two rigid rods, connected by a short rope?
I don't see the whip model, and I don't see a nunchuck 'waving'...
You're thinking too large. A whip is just a multi-segment nunchuck. If you
had a million tiny rigid segments tied together by a million tiny ropes, it
would look and act just like a whip.
But you don't. You have 2 rods, with one rope.
The limit argument doesn't apply.
I have seen reports that a whip's tip will move at near
speed of sound, when it 'cracks'. It's the same mystery
as my nunchuck question - how does that speed arise?
It's just the kinetic energy of the whole whip motion being concenctrated in
to the whip tip. The energy comes from the user's arm...
That seems clear, but...
the rest of it is just a fancy energy/motion converter that
takes slow, large-displacement
motion of one end of the whip and concentrates it to very fast,
small-displacement motion at the end. Sort of a solid-state gearbox, if
that makes any sense.
It doesn't. The "concentration of energy" pseudo-explanation
simply begs the question.
Ditto the gearbox model - gear motion is simply explained,
refering to sprocket radii as moment arms; a wheel size ratio
2:1 produces linear velocity 2:1.
OK, I'll draw a picture.
o <- Rope
|\
| \
| \
Stick A -> | \ <- Stick B
| \
| \
| \
| O <- Hand
|
You go forward, maybe with a little lead-in, and Stick B starts to
rotate, and Stick A tries to follow:
Stick A
---------------------o <- Rope
|
|
|
| <- Stick B
|
|
|
O <- Hand
If you're any good at it, you get the rope end of stick B and ALL of stick
A moving forward, with stick A vertical:
|
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|
Stick A -> |
|
|
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|
o <- Rope
/
/
/
/ <- Stick B
/
/
/
O <- Hand
This whole assembly is moving forward, with "Stick A" and "Rope" moving
the fastest to your right, in this diagram.
Suddenly, you snatch stick B back - well, all that kinetic energy in A
has to go SOMEWHERE - so it either breaks your enemy's skull or your
fingers. ;-) During that moment, Stick A is a type 1 lever, with the
fulcrum at its center of mass, and the force applied by stick in the
backwards direction, and the load at the end. so the new force being
levered from B would add to the momentum that's already there. THWACK! ;-)
Well, that's my guess. :-)
Cheers!
Rich
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| User: "hob" |
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| Title: Re: nunchuck physics |
08 Nov 2006 01:05:59 PM |
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"Sam the Bam" <samthebam1@lycos.com> wrote in message
news:1162957468.461634.129810@h54g2000cwb.googlegroups.com...
Sam the Bam wrote:
The nunchuck is a flail type weapon, common in Okinawan and
Chinese martial arts; 2 sticks, connected by a short length of
rope. Presumably everyone has seen one, sometime... if not
live, maybe a Kung Fu flick...
Watch a demo, the tip travels blindingly fast. My question is:
from a physics viewpoint, where does that speed come from?
I've been trying to model it, without success. I mean, we
know that the rim of a wheel moves faster than the hub - call
it 'radial velocity amplification' - but that doesn't explain the
chucks. The sticks are about a meter length, total, but if you
spun a one meter stick (gripping at one end), you wouldn't get
close to such speed. How does a 2" rope do the trick?
Actually a British sailor problem.
?
A nunchuck is a whip. The
connecting rope or chain is not a point pivot.
Two rigid rods, connected by a short rope?
I don't see the whip model, and I don't see
a nunchuck 'waving'...
However, that does lead me to ask: I have seen
reports that a whip's tip will move at near speed of
sound, when it 'cracks'. It's the same mystery as
my nunchuck question - how does that speed arise?
You can't explain it in terms of rotation and arm geometry...
actually, you can - it's just that energy methods are easier.
Think of you standing on a spinning schoolyard merry-go-round. When you
move your weight towards the center of the moving merry-go-round, it speeds
up due to conservation of angular momentum,
i.e., because the radius between your mass and the center of the
merry-go-round shortens, the rotational velocity must increase in order to
have the same momentum as when you were farther out.
So when you cause the handle end of a bull whip to turn in an arc, you have
"spun the merry-go-round" with the whip mass and arc diameter
-- and as the arc travels down the whip, the arc gets smaller because the
whip is smaller in diameter and thus its mass in the arcing portion gets
smaller, that smaller mass allowing the arc to be smaller, making the "end"
nof the arc section move faster due to conservation of momentum - and faster
and faster as the arc moves along the thinner and thinner whip. Until it
reaches the end and suddenly reverses the tip as the wave reflects.
A horse-whip (flexible length on a rigid stick) sends its energy into the
flexible section, amplifying the user's arm motion by effectively extending
the user's arm - a sudden reversal of the stick causes a wave, the wave
reverses at the tip, and conservation of momentum in the manner above causes
the tip to move very fast and crack.
A nun-chuck is a common older farming tool across the world. It is used to
break the grain hulls off the kernel. AKA known as a flail.
The momentum in the stick-link-stick is developed as if it were one stick,
and is stored in the three parts during the initial stroke.
Stopping the handle forces the developed rotational momentum into the
other two parts
- the link facitiltates transfer of momentum of the long three-piece stick
into the end stick and stores little itself, i.e., the original rotational
momentum is transferred into one-third the original size end stick.
The short end stick is then travelling in a smaller arc, conserving the
momentum of what was just effectively a long stick in a smaller mass AND a
smaller arc.
And on top of the conservation-of-angular-momentum increased velocity of
the end stick over that of a long single-piece stick, energy is then highest
in the tip of the end stick, since it moves the fastest in an arc ( from
ke=1/2 m V^2, )
fwiw
Sam
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| User: "Sam the Bam" |
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| Title: Re: nunchuck physics |
09 Nov 2006 02:23:07 PM |
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hob wrote:
The nunchuck is a flail type weapon, common in Okinawan and
Chinese martial arts; 2 sticks, connected by a short length of
rope.
Watch a demo, the tip travels blindingly fast. My question is:
from a physics viewpoint, where does that speed come from?
I've been trying to model it, without success. I mean, we
know that the rim of a wheel moves faster than the hub - call
it 'radial velocity amplification' - but that doesn't explain the
chucks. The sticks are about a meter length, total, but if you
spun a one meter stick (gripping at one end), you wouldn't get
close to such speed. How does a 2" rope do the trick?
I have seen reports that a whip's tip will move at near speed of
sound, when it 'cracks'. It's the same mystery as
my nunchuck question - how does that speed arise?
You can't explain it in terms of rotation and arm geometry...
actually, you can - it's just that energy methods are easier.
Think of you standing on a spinning schoolyard merry-go-round. When you
move your weight towards the center of the moving merry-go-round, it speeds
up due to conservation of angular momentum,
i.e., because the radius between your mass and the center of the
merry-go-round shortens, the rotational velocity must increase in order to
have the same momentum as when you were farther out.
So when you cause the handle end of a bull whip to turn in an arc, you have
"spun the merry-go-round" with the whip mass and arc diameter
-- and as the arc travels down the whip, the arc gets smaller because the
whip is smaller in diameter and thus its mass in the arcing portion gets
smaller, that smaller mass allowing the arc to be smaller, making the "end"
of the arc section move faster due to conservation of momentum - and faster
and faster as the arc moves along the thinner and thinner whip.
I don't follow this. The whip's mass is moving toward the
handle, like your merry-go-round analogy? What does
it mean, "whip is smaller in diameter"?
Is it crucial that the whip tapers to the end? Because
that's not the case in a nunchuk...
A pity we can't draw diagrams in this medum...
Until it reaches the end and suddenly reverses the tip as the wave reflects.
The momentum in the stick-link-stick is developed as if it were one stick,
and is stored in the three parts during the initial stroke.
Stopping the handle forces the developed rotational momentum into the
other two parts
- the link facitiltates transfer of momentum of the long three-piece stick
into the end stick and stores little itself, i.e., the original rotational
momentum is transferred into one-third the original size end stick.
The short end stick is then travelling in a smaller arc, conserving the
momentum of what was just effectively a long stick in a smaller mass AND a
smaller arc.
I think I get this. Angular momentum is reduced in the
handle, which by conservation, must appear in the load
stick. I have trouble picturing how this energy transfer occurs,
though... it's not a wire conducting electricity, or heat diffusion...
And logically, per this argument, the handle must be
decelerated to accelerate the load - which means
no velocity gain occurs while the user twirls the handle
at constant speed? That contradicts perception, if not reality...
Sam
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| User: "hob" |
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| Title: Re: nunchuck physics |
09 Nov 2006 04:31:32 PM |
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"Sam the Bam" <samthebam1@lycos.com> wrote in message
news:1163103787.411547.194870@e3g2000cwe.googlegroups.com...
hob wrote:
The nunchuck is a flail type weapon, common in Okinawan and
Chinese martial arts; 2 sticks, connected by a short length of
rope.
Watch a demo, the tip travels blindingly fast. My question is:
from a physics viewpoint, where does that speed come from?
I've been trying to model it, without success. I mean, we
know that the rim of a wheel moves faster than the hub - call
it 'radial velocity amplification' - but that doesn't explain the
chucks. The sticks are about a meter length, total, but if you
spun a one meter stick (gripping at one end), you wouldn't get
close to such speed. How does a 2" rope do the trick?
I have seen reports that a whip's tip will move at near speed of
sound, when it 'cracks'. It's the same mystery as
my nunchuck question - how does that speed arise?
You can't explain it in terms of rotation and arm geometry...
actually, you can - it's just that energy methods are easier.
Think of you standing on a spinning schoolyard merry-go-round. When you
move your weight towards the center of the moving merry-go-round, it
speeds
up due to conservation of angular momentum,
i.e., because the radius between your mass and the center of the
merry-go-round shortens, the rotational velocity must increase in order
to
have the same momentum as when you were farther out.
So when you cause the handle end of a bull whip to turn in an arc, you
have
"spun the merry-go-round" with the whip mass and arc diameter
-- and as the arc travels down the whip, the arc gets smaller because
the
whip is smaller in diameter and thus its mass in the arcing portion gets
smaller, that smaller mass allowing the arc to be smaller, making the
"end"
of the arc section move faster due to conservation of momentum - and
faster
and faster as the arc moves along the thinner and thinner whip.
I don't follow this. The whip's mass is moving toward the
handle, like your merry-go-round analogy? What does
it mean, "whip is smaller in diameter"?
Is it crucial that the whip tapers to the end? Because
that's not the case in a nunchuk...
A pity we can't draw diagrams in this medum...
Until it reaches the end and suddenly reverses the tip as the wave
reflects.
The momentum in the stick-link-stick is developed as if it were one
stick,
and is stored in the three parts during the initial stroke.
Stopping the handle forces the developed rotational momentum into the
other two parts
- the link facitiltates transfer of momentum of the long three-piece
stick
into the end stick and stores little itself, i.e., the original
rotational
momentum is transferred into one-third the original size end stick.
The short end stick is then travelling in a smaller arc, conserving the
momentum of what was just effectively a long stick in a smaller mass AND
a
smaller arc.
I think I get this. Angular momentum is reduced in the
handle, which by conservation, must appear in the load
stick. I have trouble picturing how this energy transfer occurs,
though... it's not a wire conducting electricity, or heat diffusion...
And logically, per this argument, the handle must be
decelerated to accelerate the load -
momentum is built up - it remains in the system and is redistributed by
slowing the handle
which means
no velocity gain occurs while the user twirls the handle
at constant speed? That contradicts perception, if not reality...
twirl the handle at constant speed and watch the end - there is no velocity
gain.
Sam
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| User: "Rich Grise" |
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| Title: Re: nunchuck physics |
10 Nov 2006 07:37:54 PM |
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On Thu, 09 Nov 2006 12:23:07 -0800, Sam the Bam wrote:
hob wrote:
The nunchuck is a flail type weapon, common in Okinawan and
Chinese martial arts; 2 sticks, connected by a short length of
rope.
Watch a demo, the tip travels blindingly fast. My question is:
from a physics viewpoint, where does that speed come from?
I've been trying to model it, without success. I mean, we
know that the rim of a wheel moves faster than the hub - call
it 'radial velocity amplification' - but that doesn't explain the
chucks. The sticks are about a meter length, total, but if you
spun a one meter stick (gripping at one end), you wouldn't get
close to such speed. How does a 2" rope do the trick?
I have seen reports that a whip's tip will move at near speed of
sound, when it 'cracks'. It's the same mystery as
my nunchuck question - how does that speed arise?
You can't explain it in terms of rotation and arm geometry...
actually, you can - it's just that energy methods are easier.
Think of you standing on a spinning schoolyard merry-go-round. When you
move your weight towards the center of the moving merry-go-round, it speeds
up due to conservation of angular momentum,
i.e., because the radius between your mass and the center of the
merry-go-round shortens, the rotational velocity must increase in order to
have the same momentum as when you were farther out.
So when you cause the handle end of a bull whip to turn in an arc, you have
"spun the merry-go-round" with the whip mass and arc diameter
-- and as the arc travels down the whip, the arc gets smaller because the
whip is smaller in diameter and thus its mass in the arcing portion gets
smaller, that smaller mass allowing the arc to be smaller, making the "end"
of the arc section move faster due to conservation of momentum - and faster
and faster as the arc moves along the thinner and thinner whip.
I don't follow this. The whip's mass is moving toward the
handle, like your merry-go-round analogy? What does
it mean, "whip is smaller in diameter"?
Is it crucial that the whip tapers to the end? Because
that's not the case in a nunchuk...
A pity we can't draw diagrams in this medum...
Until it reaches the end and suddenly reverses the tip as the wave reflects.
The momentum in the stick-link-stick is developed as if it were one stick,
and is stored in the three parts during the initial stroke.
Stopping the handle forces the developed rotational momentum into the
other two parts
- the link facitiltates transfer of momentum of the long three-piece stick
into the end stick and stores little itself, i.e., the original rotational
momentum is transferred into one-third the original size end stick.
The short end stick is then travelling in a smaller arc, conserving the
momentum of what was just effectively a long stick in a smaller mass AND a
smaller arc.
I think I get this. Angular momentum is reduced in the
handle, which by conservation, must appear in the load
stick. I have trouble picturing how this energy transfer occurs,
though... it's not a wire conducting electricity, or heat diffusion...
And logically, per this argument, the handle must be
decelerated to accelerate the load - which means
no velocity gain occurs while the user twirls the handle
at constant speed? That contradicts perception, if not reality...
Dang, it's such a kewl thread, I don't know what to snip!
Imagine a baseball pitcher throwing a ball at 98 MPH. His arm
is doing "crack the whip" much like a nunchuk. He focuses
all of his momentum on his arm. and when he comes to a stop,
his arm becomes a lever and flings ALL of that angular momentum
into the mass of the ball.
The way I see it, the player's forearm just acted like the far
stick of a nunchuk - the whole thing is going forward, then
suddenly one end is snatched back - that will at least double
the velocity^H^H^H^H^H^H^H^Hspeed of the other end, depending
on where its center of mass is.
This is why, when you do that with a nunchuk, you'd better be
darn sure and hit what you're swinging at, because when it
comes back and nails your elbow, it really, really hurts. ;-)
I have no math or training to back any of this up, it just seems
intuitive to me. (well, I have some math and some training, but
I'm not gonna tackle this one with arithmetic!)
Cheers!
Rich
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| User: "Sam the Bam" |
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| Title: Re: nunchuck physics |
09 Nov 2006 01:54:15 PM |
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Sam the Bam wrote:
A nunchuck is a whip. The
connecting rope or chain is not a point pivot.
I was thinking about this some more, and wonder:
would a nunchuk perform differently, if it had a
hinge, in lieu of a rope?
Sam
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| User: "hob" |
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| Title: Re: nunchuck physics |
09 Nov 2006 04:25:16 PM |
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"Sam the Bam" <samthebam1@lycos.com> wrote in message
news:1163102055.347881.241860@k70g2000cwa.googlegroups.com...
Sam the Bam wrote:
A nunchuck is a whip. The
connecting rope or chain is not a point pivot.
I was thinking about this some more, and wonder:
would a nunchuk perform differently, if it had a
hinge, in lieu of a rope?
no
Sam
.
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| User: "Rich Grise" |
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| Title: Re: nunchuck physics |
10 Nov 2006 07:23:02 PM |
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On Thu, 09 Nov 2006 16:25:16 -0600, hob wrote:
"Sam the Bam" <samthebam1@lycos.com> wrote in message
Sam the Bam wrote:
A nunchuck is a whip. The
connecting rope or chain is not a point pivot.
I was thinking about this some more, and wonder:
would a nunchuk perform differently, if it had a
hinge, in lieu of a rope?
no
Gimme a break. Imagine a stick about the size of a relay
race baton (maybe 15" long, 1.5" diam), and attach another
just like it at the end, with a rope. Now hold the one
out in front of you, with the other one dangling from the
rope. Now twirl it in a circle.
Now, do the same thing with a hinge instead of a rope, and
it won't twirl unless you let it rotate in your hand. IOW,
it needs both degrees of freedom.
I don't know how to explain the crack-the-whip effect; it
seems almost intuitive to me.
The stick with the lead weight in the middle is pretty easy -
you impart velocity in one direction, quickly stop the near
end and even pull back, and the center of mass of the lead
weight is the fulcrum of a lever which exchanges force for
distance.
Nunchuks and whips use pretty much the same principle, except
that the mass is distributed over the length of the whip, and
with nunchuks the movement of the hand is very instrumental in
doing those tricks. It's like thwacking somebody with a towel
in gym class. ;-)
If you're trying to show off, twirling it all around and at
at all angles, it hurts like a motherf***er when you whack
your own elbow. :-)
Cheers!
Rich
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