karela said:
When we go upstairs we spend a lot of energy that gets stored as potential
energy. When we go downstairs we waste all the potential energy. Couldn't
anyone invent a good way of coming down so the potential energy could be
converted to other forms of energy that could be converted to electricity
when needed??
Well in *theory*, yes you certainly could. Something as simple as a bucket
and rope tied to a pulley turning a shaft. When you want to go downstairs
you just climb into the bucket and let it lower you through a hole in the
floor. Of course there will be *some* losses.
But lets look at just how much energy we're talking about. Raising a 200
lbm man up 10 feet in normal gravity would put 2000 ft-lbf of energy into
the man. If you could recover *all* of that, that is a mere 0.75 watt-hours
(not kW-hr, just watt-hour). So if he goes up the stairs 20 times a day for
a year, he'll have used 20*365*.75 / 1000 = 5.5 kW-hr of energy. Recover
*all* of that perfectly and you have about $1 worth of electricity for the
year.
Going up stairs 20 times a day is great exercise, but it won't generate much
energy for you.
daestrom