Teaching Students About Static Charge
Teaching Students About Static Charge
Goal
We wanted to teach an audience of middle school students that electrons can build up on materials and objects. We wanted them to understand that this happens by transferring elections from one type of material to another. Not only this, but already built-up electrons can disperse, effectively discharging the object, taking the object back to neutral.
In general, this was achieved by calling attention to well-known phenomena, like static-laden clothing, the electric shocks that people feel when walking in dry rooms on carpets, and lightening.
The Demonstration
For our project, we demonstrate the build up of electrons using showing off a large Van de Graff generator. To extend the demonstration, the audience is able to assemble smaller do-it-yourself Van de Graff generator kits. The entire demonstration will be made available to use for the Summer Engineering Experience for Girls (SEE) camp in future years.
Manufacturing
Design
The design is based on the basic arrangement for a Van de Graff Generator. The goal of the design, versus other production Van de Graff generators was to make visible all the internal workings of a Van de Graff generator. After an initial paper sketch, Computer Aided Design (CAD) tools were used to create a 3D representation of the final product. All models created were listed with accompanying materials that were specified to proper dimension in order to minimized fabrication time.
Fabrication and Assembly
Fabrication included relatively simple processes, the most complicated of which included the use of a machine lathe and a vertical mill. Referencing dimensions from the CAD model and drawings allowed the assembly to be finished within a number of hours.
Changes During Assembly
Initial design included channeled rollers with a depressed surface to “hold in” the insulating belt. Upon completion of this design it was discovered that this method actually caused the belt to immediately travel to one side and jam, stopping the rotation of the belt. The rollers were redesigned with the opposite profile. This crowned roller provided a self straightening mechanism built into the belt and roller system.
Problems Encountered
The final product proved to be inadequate to function to its expected performance. Largely due to the selection of a motor that was unable to provide adequate torque to spin the belt at a high enough rate.
Ian Norman and Lucy Terrell
Carnegie Mellon University
May 2008