Where the Energy Goes: teacher key

Gas and Electric Cars, grade 10 edition, written for 10th grade. Most of a gas car's fuel energy never moves the car. Follow the energy through both kinds of car, and see how their motors and layouts differ.

Read the book. Print this page for the key.

Questions and answers

1. What does a flywheel do in a piston engine?
   • It lights the fuel
   • It charges the battery
   • It keeps power flowing to the drive train steadily (answer)
2. As of November 2026, what share of the grid's electrical energy do EVs convert to power at the wheels?
   • About 12%
   • Over 77% (answer)
   • Under 5%
3. In a series plug-in hybrid, what turns the wheels?
   • Only the electric motor (answer)
   • Only the gasoline engine
   • A flywheel
4. Which layout powers each wheel separately?
   • A single large motor with a differential housing
   • Two smaller motors with independent drive shafts (answer)
   • A gasoline engine and a tailpipe
5. What happened to electric cars on U.S. roads by 1935?
   • They all but disappeared (answer)
   • They made up a third of vehicles
   • They first appeared

Words

• flywheel: energy-storing wheel
• differential: wheel speed gear
• hybrid: engine-motor car
• generator: makes electricity
• stroke: one piston move