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Name: Denise A.
Status: educator
Age: 50s
Location: N/A
Country: N/A
Date: Thursday, August 22, 2002


Question:
At Australia's Wonderland Theme Park there is a ride that elevates a carriage of 4 seats up a tower 67 meters high. The carriage 'free falls' until the braking system comes into play. Apparently, 6 meters above the ground there are metal fins attached to the bottom of the tower which "disrupt a magnetic field generated by pairs magnets on each seat". (The pairs of magnets on each seat are positioned with unlike poles facing and the tower fin comes between them). I cannot understand how the disruption of the magnetic field fins effectively causes a repulsion and hence the carriage to come to a stop. ( I am a junior science teacher and a biologist not a physicist!)


Replies:
Denise,

This will take a little imagination. First, magnetic force vs magnetic field. The magnetic force felt by an object is perpendicular to the field and to the object's motion relative to the field. When the field approaches the top of the fin, the field "sees" the fin as moving upward. Let us assume the field is directed into the screen: north pole in front and south pole behind the screen. The negatively charged free electrons in the bottom of the fin start moving to the right. The force on these rightward electrons is down. To prevent a huge charge build-up, electrons below the magnet continue around, making a complete circle: an eddy current.

Any moving charge creates a magnetic field around it. A circle of current creates a magnetic field very much like that of a bar magnet. Electrons moving in a clockwise circle "look like" a bar magnet with its north pole in front of the screen and its south pole behind the screen. This "induced magnet" is just below our original magnet, with like poles close together. Like poles repel. The metal is pushed down and the seat magnet is pushed up.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College


Dear Denise,

Since I do not have any schematics on the braking system I can only hazard a guess. Maybe some of my colleagues will come up with something a little more concrete. Anyway here is my theory of the ride sight unseen:

I would imagine that it would have to act like a mag lev train or a ride called Superman here in the states. On the Superman, there are magnets in a line on the track. Polarity of each magnet is switched as the car passes over each spot. At the front of the car the magnets are opposite poles to draw the car along by attraction and at the backend of the car the magnets are the same pole in order that the repulsion pushes it along as well. The polarity of each magnet must be switched as the car passes over it. This can give quite a fast acceleration.

I am not sure what the fins on your ride do. Somehow the magnet poles would have to be the same pole in the front of the car to repel and thus slow down the car, while at the back, they would have to be opposite poles to attract in the upward direction in order to slow the car's descent. Perhaps the fins trigger some sort of switch that reverses the magnet's polarity.

You might write to the Wonderland Theme Park, explain that you are an educator and are looking for explanation for you kids. I will bet they'd be happy to give you a little more detailed explanation. Many of the parks around here have Physics days. They have student level explanations of the rides as well as providing a fun day out.

One of my colleagues wrote a book that you might find useful. It is Amusement Park Physics by Nathan A. Unterman. (J. Weston Walch, Publishers)

Good luck on your "amusing" search.

Martha Croll



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