27 April 2006
SETI League
PriUPS Project


A CATWOKE* Rumination

Driving downhill is a waste of energy.  Literally.  At the top of the hill, you and your car have potential energy.  It is converted to kinetic energy as you go down the hill, and unless the hill is very short or shallow, you have to use your brakes to keep your speed reasonable.  I hate brakes!  At least with a hybrid vehicle some of the energy that would otherwise be wasted is used to charge a battery, which helps you get back up the hill.  With normal cars, brakes simply turn your gasoline into useless heat.

Going up the hill, you use extra gas since you're raising the car in a gravity field, which adds to its potential energy.  It's been said many times that "gravity sucks."  And yet in this case, it's generally benign.  The gravitational field is said to be "conservative" because energy used to raise an object can be recovered when lowering the object.  This is why a pendulum works, for example.  So why do we spend energy going uphill, and waste it going down?  How about:

  • Instead of having hills, have platforms.  A car gets on a platform at the top and is lowered to the bottom.  The potential energy is used to spin up a giant flywheel, whose energy is then coupled to a platform used by a car going from the bottom to the top.
  • Cars are metallic.  Create an electromagnetic braking field.  Just as it's harder to turn a generator armature when the generator is driving a load, the car will go slower in the field, and the "generator" will drive a load, such as a flywheel or battery, or perhaps a reverse field that will help a car going uphill.
  • Keep a car on the top of a hill and one on the bottom.  Use a people elevator and switch cars.

Does any of this make practical sense?  Probably not, although the second isn't entirely out of the question.  But it's fun to think about saving energy, and more than you think is wasted on hills.  It's certainly easier to write about this than to come up with a practical method.  (I suppose moving to Florida isn't entirely impractical, and solves the hill problem handily.)

*Citizens Against the Waste of Kinetic Energy

Richard Factor