Simple systems are controlled by one, or a few, parameters. Step on the accelerator, and the car speeds up (other things being equal). Warm the bread dough, and the yeast cells divide quicker (within limits). Increase the speed of a projectile, and it flies farther (ignoring other issues).
Complex systems are controlled by a large number of factors, sometimes so many that building an accurate predictive model is virtually impossible. (Global climate may be one such case.) But often, within a given regime, one parameter clearly dominates. (For the Earth's climate today, carbon dioxide is probably that parameter.)
Consider running — unaided human locomotion. For various overlapping distance ranges I naïvely speculate:
| miles | limiting factor |
| 0 - 0.2 | mechanical force — accelerating the mass of the body |
| 0.1 - 2 | oxygen intake — getting enough oxidizer to the cells |
| 0.5 - 10 | waste removal — carrying off lactic acid or other muscle activity byproducts |
| 5 - 30 | stored energy — metabolizing fuels already present in the body |
| 15+ ... | fuel input — absorbing additional sugars via digestive system |
| 20+ ... | electrolyte balance — maintaining proper concentrations of Na, K, etc. |
| 30+ ... | mechanical breakdown — blistering, bruising, joint damage, etc. |
| 50+ ... | brain chemistry — continuing key mental functions |
(cf. PushingTheEnvelope (25 Aug 1999), EnvelopePushing (24 Apr 2003), ...)
TopicRunning - TopicScience - 2006-10-16
(correlates: DelicatePower, SafetyFirst, ChivalrousReasoning, ...)