Energy and Thermodynamics

• The First Law of Thermodynamics -- the study upon which all physical science as we know it is based -- states that energy can never appear or disappear, it can only change forms. Put another way, all the energy in this universe has to come from somewhere and it has to go somewhere. The Second Law, known by its shorthand "entropy," states that no energy conversion is perfect, and that every energy conversion results in a certain amount of waste.
  
  

Types of Energy in a Car

• Gravity created heat (thermal energy), and the heat on our Earth allowed for the growth of organisms. That growth converted the sun and Earth's heat into chemical energy stored as hydrogen, carbon and oxygen in the organism. When that organism died, it turned into oil (still chemical energy), which gets burned in the engine and converted to kinetic energy (movement of the crankshaft) and waste heat. When you hit the brakes in your car, all of that kinetic energy gets scrubbed off and converted to thermal energy (via friction) in the brake pads and rotors.
  
  

Electric vs. Gas Efficiency

• Gasoline contains a certain amount of energy per gallon -- specifically, about 114,000 British Thermal Units. An average gasoline engine only converts about 30 percent of the fuel's energy potential into forward motion (kinetic energy); the rest gets burned up as waste heat and friction. An electric motor and battery combination are vastly more efficient, upwards of 85 to 95 percent, which is the primary reason that electric cars and cars that use some sort of electric power to contribute kinetic energy (hybrids) end up being more fuel efficient than a pure-gas automobile.
  
  

Power Generation

• According to the First Law, that efficient electric motor's power has to come from somewhere. The battery pack isn't just going to recharge itself. The other key component to hybrid fuel efficiency lay in their braking strategy; instead of converting useful kinetic energy into useless heat, hybrid drive systems activate a circuit that turns their electric motors into generators. The drag of the generator slows the car, and the kinetic energy from the car goes through the generator to become stored chemical energy in it's battery pack. So, the hybrid wins twice -- the braking system recaptures most of the energy lost during braking, and the motor makes efficient use of it afterward.