TANKSALE is a model (Figure IV-5a) of mining and use of a nonrenewable source (Q), like coal, oil, or copper. Money received for the product is used to pay for necessary inputs, profits, costs, etc. The mining company uses purchased goods and services (F) to mine, sort, store, and transport the product. The reserve in the ground (Q) is slowly renewed by the geological processes (K1*E). Since use is much faster than its renewal, we call it a "non-renewable" resource.

At first with an abundant supply of source reserves, large quantities are mined with little effort, not using many goods and services. With set prices for the yield, (P1) and for necessary goods and services (P2), the company makes money. Later when reserves are less available, yield is less, and sales are less than what is required to maintain the mining process. The operation stops; some ore may be left in the ground.

Examples of Economic Use of Reserves

This model represents use of any source where use is much faster than its renewal. Other examples are natural gas, gold, uranium, phosphate for fertilizer, slow growth forests, and soils where agriculture is not based on land rotation.

"What If" Experimental Problems

1. How do the money (M) and storage (Q) react if the price you receive for the yield is increased? Change P1 to 7.
   


2. Will the operation get started if you begin with-almost no capital? (M = 0)? How would it be different if you had twice as much capital as the original program? Change M to 2.
   


3. What is the effect of finding more reserves after the operation has been going 100 months? Type a new statement to increase Q in 300 more units
   


4. What would happen if the initial reserve were small and less available? Make Q = 300.

COMPUTER MINIMODELS AND SIMULATION EXERCISES FOR SCIENCE AND SOCIAL STUDIES

Howard T. Odum* and Elisabeth C. Odum+
* Dept. of Environmental Engineering Sciences, UF
+ Santa Fe Community College, Gainesville

Center for Environmental Policy, 424 Black Hall
University of Florida, Gainesville, FL, 32611
Copyright 1994

Autorização concedida gentilmente pelos autores para publicação na Internet
Laboratório de Engenharia Ecológica e Informática Aplicada - LEIA - Unicamp
Enrique Ortega
Mileine Furlanetti de Lima Zanghetin
Campinas, SP, 20 de julho de 2007