Putting Trees on Cruise Control

摘要

WHEN YOU GET IN YOUR CAR, YOU START IT UP, press the pedal down, and get up to speed. But once you get going, it's easy to keep the car up to speed. Just a little constant pressure on the pedal — a little constant infusion of energy — is all it takes. But if you have a big obstacle in your way (like tough terrain or a hill), the car takes more energy to maintain speed. If you let the car slow down, it requires extra energy to get back to that constant speed.