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SESK: Stuff Everyone Should Know · sesk.info/eng-efficiency-motor-vs-engine

Which typically converts input energy into useful work most efficiently?

A large electric motor, up to about 98%, versus about 30% for a gasoline engine.

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  1. A gasoline car engine
  2. A large electric motor ✔
  3. They are about equal

Why: Efficiency is useful work out divided by energy in. Most of a gasoline engine's fuel energy leaves as heat, while big electric motors waste very little.

Huh, didn't know that: No real machine reaches 100% efficiency; some energy becomes heat through friction and other losses.

The dad joke
I'm 98% efficient, like an electric motor. The other 2% is coffee breaks.
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References

Answer: A large electric motor. Efficiency is useful work out divided by energy in. Most of a gasoline engine's fuel energy leaves as heat, while big electric motors waste very little.

  1. OpenStax College Physics 2e: 7.6 Conservation of Energy (Table 7.2) openstax.org/books/college-physics-2e/pages/7-6-conservation-of-energy
    Efficiency = useful energy or work output / total energy input. Gasoline engine 30%; Electric motor 98%
    Checked 2026-10-10.

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