## Friday, November 30, 2012

### Hybrid Cars

By Andrew Long

When going down a hill, you have to hit the breaks in order to not quickly accelerate (this creates energy lost as heat, keeping kinetic energy constant while decreasing the potential energy of the car). When you go back up a hill, you have to put a significant amount of energy to keep the kinetic energy constant while increasing the gravitational potential energy. I wanted to see if there was a way that you could reduce the amount of energy needed to go up and down a hill.
It turns out that, using a flywheel; it is ideally possible to spend no energy going up and down two equivalent hills. Using a flywheel in a car, as you go down a hill and apply the “breaks” to the car, you slow down the car (as potential energy turns to kinetic energy) by applying torque to the flywheel. As the flywheel spins, the wheel can create energy in the form of electricity. This is what they use in hybrids like the Toyota Prius.

Sample calculations

mgh=(1/2)mv02+electricity stored by the flywheel.
(6000kg)(9.8m/s2)(60m) turns completely into electrical energy. This energy is used to get back up the hill.
(1/2)(6000kg)(13.4m/s)2 this amount of energy is kept the same throughout the entire ride down the hill.

http://www.economist.com/node/21540386