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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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