The Engineering of Motion: teacher key

Gas and Electric Cars, grade 12 edition, written for 12th grade and up. A century of engines and motors, from a hand crank to regenerative braking: the principles, the numbers and the trade-offs inside gas and electric cars.

Read the book. Print this page for the key.

Questions and answers

1. As of November 2026, what share of the energy in a conventional car's fuel moves it down the road?
   • Over 77%
   • About 12% to 30% (answer)
   • About 94%
2. Why must spark timing be precise in a gas engine?
   • Ignition that is too early makes the engine knock (answer)
   • The battery would drain
   • The motor would spin backward
3. What does a flywheel do in a piston engine?
   • It lights the fuel
   • It keeps power flowing to the drive train steadily (answer)
   • It cools the battery
4. What does the commutator in a DC motor do?
   • It charges the battery
   • It lights the fuel
   • It reverses the current each half turn so the rotor can spin continuously (answer)
5. Why does regenerative braking offer little advantage on the highway?
   • Highway driving has little braking (answer)
   • Motors stop at high speed
   • Highways have no brakes
6. Which of these words from the book is closest to "regenerative"?
   • Energy-returning (answer)
   • Fuel-burning
   • Spark-making

Words

• efficiency: energy used well
• octane: fuel rating
• flywheel: energy-storing wheel
• commutator: current reverser
• differential: wheel speed gear
• regenerative: energy-returning