Elevators are all about energy

[yufangfang]

Scientifically, elevators are all about energy. To get from elevator factory the arena to the 18th attic walking up stairs you accept to move the weight of your physique adjoin the downward-pulling force of gravity. The activity you expend in the activity is (mostly) adapted into abeyant energy, so aggressive stairs gives an access in your abeyant activity (going up) or a abatement in your abeyant activity (going down). This is an archetype of the law of attention of activity in action. You absolutely do accept added abeyant activity at the top of a architecture than at the bottom, even if it doesn't feel any different. To a scientist, an elevator is artlessly a accessory that increases or decreases a person's abeyant activity after them defective to accumulation that activity themselves: the elevator gives you abeyant activity if you're traveling up and it takes abeyant activity from you if you're advancing down. In theory, that sounds simple enough: the elevator will not charge to use abundant activity at all because it will consistently be accepting aback as abundant (when it goes down) as it gives out (when it goes up). Unfortunately, it's not absolutely that simple. If all the elevator had were a simple elevate with a cage casual over a pulley, it would use ample amounts of activity appropriation humans up but it would accept no way of accepting that activity back: the activity would artlessly be absent to abrasion in the cables and brakes (disappearing into the air as decay heat) if the humans came aback down.