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Tornado Effect
Name: Alex W.
Status: other
Age: 20s
Location: N/A
Country: N/A
Date: 2000-2001
Question:
Tornado Effect
I've heard stories about tornados shoving drinking straws through phone
poles and brick walls. Is the reason for this known? I am curious what
would be discovered if I constructed a large ring, weighted heavily
(tons?), spun it at extreme speeds, and tested the maliability of metals
placed within the center of the spinning ring.
Replies:
You have asked two questions:
1. About the tornado. The mechanical properties of a projectile
depends on its speed. For example, if I take a soft lead bullet and press it
slowly against a steel plate, say 0.5 cm thick, using a mechanical press, it
would deform into a lead disc and the steel plate would be largely
unaffected. However, if I take the same soft lead bullet and it's fired from
a 0.357 Magnum, it would easily blow a large hole in the same steel plate.
The difference is that deformation of a projectile takes a certain amount of
time to occur. If the impact time is very short compared to this
characteristic time of deformation, the mechanical properties of the object
will be very different. This is not an uncommon phenomenon. Another example,
if I jump into a lake from a height of 1 meter, I just sink and make a
splash -- no harm. But if I jump into the same lake from an airplane at 1000
meters above the surface, I'm a pancake. I might just as well hit solid
ground. The reason is: at the speed with which I hit the water is so fast,
the water does not have time to "get out of the way" so it becomes
essentially a solid. This is what happens to straws etc. driven by tornadic
winds. They become projectiles, like an arrow.
2. The high speed rotary press you describe is cerainly feasible, but it
would be a difficult machine to build and it is not clear what you would
learn that you do not learn from a conventional press, which is relatively
simple and inexpensive.
Vince Calder
Alex,
This is based on what many textbooks refer to as the normal force, the force
the surface of a solid object exerts to prevent another object from passing
through it. Every surface has a maximum normal force. It can push no
harder than its maximum. A straw moving at an incredible speed hits the
phone pole. The pole pushes on the straw with its maximum force. Time is
required to stop the straw. In that time, the straw moves a distance into
the telephone pole.
Force provides acceleration. Acceleration over time provides a change of
velocity.
As for the question regarding malleability, what you are speaking of is a
centrifuge. One method is to attach a weight (tons are not necessary) to a
wire. Have the weight set on a rotating stand. Make sure the weight move.
One option is to mount it like a pendulum at approximately the radius you
want. Connect the metal wire from the hanging weight to the center fo the
rotating platform. Be sure the wire is taught, no bends. Spin the platform
to a significant speed. Measure the new radius while spinning, perhaps with
a ruler mounted on the platform. The force exerted on the wire is (mass of
hanging weight)(speed of weight)^2/(radius of weight's position). Textbooks
call it centripetal force for circular motion.
Dr. Ken Mellendorf
Illinois Central College
Straws are able to go through telephone poles,
obviously, because of their extreme speeds. I do not
see the connection between this phenomenon and your
idea with the iron ring.
If the ring were to spin rapidly, I suppose that it
will have no bearing on any object you place at its
center, with the exception of the wind created by the
spinning. Friction from the wind may increase the
temperature, thus increasing the malleability of the
metal.
A more interesting experiment may involve a magnetic
field, and if the ring were not spinning perfectly
about its axis.
Hope this helps
-Wil
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