In juggling books it is often said that when juggling
torches, they behave differently when lit due to the
fact that the fire will cause increased friction resistance
in the air. I really wonder if that statement is not a
myth. So my question is simply: Is there a scientific 
basis for claiming that torches behave differently when lit
due to increased friction towards the air?

Interesting question. It certainly seems as if they are going slower,
but that could just be a perception.

I have just burned a few holes in the rug because I was watching the
flaming end instead of the one I should catch, and the place smells of
gasoline.  The wife will not be pleased at all ...

For one thing, the gasoline  - or what ever you use - increases the
weight of one end of the batton, shifting the center of gravity
towards that end so that the lighter end will describe a larger circle
than it did before, while the wet end  would describe a smaller
circle, rotating once in the same period of time, and obviously then
moving slower, since its circle had a smaller radius and
circumference.
Since people probably don't train with the torch end wet, this alone
could account for the difference  - in theory, anyway.
If you tell us that the books say one should train with battons
weighted to account for this, and they still say flaming torches move
differently, I will have to develop theory B.

I believe that the flame - the sphere of hot air around the end -
creates a larger "profile" to be moved through the cooler air; the
burning end thus having to displace more cold air as it moves.  That
would indeed then be increased friction with the air;  just as larger
pingpong ball would slow down more quickly than a smaller one.

Hey, I like that.  Now someone who really knows can come and tell us
what really happens.  I would trust the jugglers to know that there
really is a difference.

I fully agree with the idea that fueled torches behave differently
than dry ones. The question concerns any difference that would occur
when lighting the torches not fueling them.

When we have discussed this concept we have thought about building
a trebuchet, dipping 100 tennis balls in kerosene and shooting them
in the park to measure their flight distance. The experiment would then
be repeated by putting fire to the tennisballs before shooting them
in the park.

Especially, the last step might not be appreciated by other visitors
in the park. So I figured that asking the question might be a simpler
way of finding the answer.

I like that idea  - after I looked up "trebuchet" -

What about a simpler machine, something like in circus performances in
which a persons jumps on one end of the lever and the other flies up.

To assure that the same force is applied, drop a heavy object from the
same height.  Put something under that end of the lever so that it
stops before reaching the horizontal and your flaming balls fly at an
angle.  This will not save you from having to dodge fall balls but
will allow easier observation: height when the ball reaches the
highest point; how far it flies; time from start to landing (though
that remain the same).  You could easily control the area needed -
probably not more than a tennis court in size.
I think gasoline would burn hotter than kerosene, but you would have
to experiment with what happens to the balls, maybe slit them so that
they don't explode.  Hmmm?  Rocket effect then, affecting the flight
regardless of its direction??

(Sounds fun!  Nice thing to entertain folks at the beach in the evening.)
I'd talk to the authorities before the final experiment of shooting flaming balls.

If you don't cancel the question, you can come back and post the results.  :-)
If you include our names, that brings the question back into view.

Good luck!

You could verify this experimentally in a less dangerous manner by
making a flaming/non-flaming pendulm. My physics on the macroscale are
a bit rusty, but an alternative would be to tether a flaming/ non
flaming ball to a motor, such that the a horizontal circle is
described by the path of the ball. If the friction is really greater
while on fire, the ball should cicrle the motor at lower level. You
could also try this yourself by holding a tethered club one flaming
-one not- in each hand, and seeing which rises higher.


Trebuchet. Heh. Yeah, I don't think the ranger would like that Yogi.

"Fire" is not a physical object, it's just air that has been heated
until it glows.  A moving burning torch does not "drag" the flame
behind it, and I have a hard time figuring out how the fact that it
was lit would make a significant difference (the weight of the fuel
would, as has been pointed out).

The flame will heat air, which will rise and generate a small amount
of lift, but I don't think there would be enough to cause a noticeable
difference.

To be honest, I wonder too, but if the jugglers say so ...
I hope we get a comment about the tennis ball experiment.

I have tried a 
SEARCH TERM: thermal boundary layer

and got  links which seems to indicate that you get more 
turbulence at the surface of a hot object:
http://apollo.lsc.vsc.edu/classes/met130/notes/chapter10/therm_turb.html

How about that?