Motor v. Engine: What’s the Difference?

by Kate Repantis on October 28, 2014 · 1 comment

in Engineering

Guest Post by Sarah Jensen from the Ask an Engineer series, published by MIT’s School of Engineering

As with almost any word, it all depends how far you go back in time for your definition…

NASA's J-2X rocket engine takes a Halloween plunge into an icy cauldron of liquid nitrogen. Photo: Pratt & Whitney Rocketdyne

NASA’s J-2X rocket engine takes a Halloween plunge into an icy cauldron of liquid nitrogen. Photo: Pratt & Whitney Rocketdyne

As technologies and devices evolve, language must stay on its toes if we expect to understand each other when we talk about them. English-speakers are particularly flexible at adapting to progress. They’re willing to coin new terms, modify old meanings, and allow words that are no longer useful to pass from common usage. “The etymologies of ‘motor’ and ‘engine’ reflect the way language evolves to represent what’s happening in the world,” says MIT Literature Professor Mary Fuller.

The Oxford English Dictionary defines “motor” as a machine that supplies motive power for a vehicle or other device with moving parts. Similarly, it tells us that an engine is a machine with moving parts that converts power into motion. “We use the words interchangeably now,” says Fuller. “But originally, they meant very different things.”

“Motor” is rooted in the Classical Latin movere, “to move.” It first referred to propulsive force, and later, to the person or device that moved something or caused movement. “As the word came through French into English, it was used in the sense of ‘initiator,’ ” says Fuller. “A person could be the motor of a plot or a political organization.” By the end of the 19th century, the Second Industrial Revolution had dotted the landscape with steel mills and factories, steamships and railways, and a new word was needed for the mechanisms that powered them. Rooted in the concept of motion, “motor” was the logical choice, and by 1899, it had entered the vernacular as the word for Duryea and Olds’ newfangled horseless carriages.

“Engine” is from the Latin ingenium: character, mental powers, talent, intellect, or cleverness. In its journey through French and into English, the word came to mean ingenuity, contrivance, and trick or malice. “In the 15th century, it also referred to a physical device: an instrument of torture, an apparatus for catching game, a net, trap, or decoy,” says Fuller. Read more

Visit the MIT School of Engineering’s Ask an Engineer site for answers to more of your questions.

{ 1 comment… read it below or add one }

Steve Cohen October 30, 2014 at 5:01 pm

I’d say generally an engine drives a vehicle, while a motor moves a smaller subsystem.

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