The Physics Law We Misread For Hundreds Of Years

Isaac Newton was arguably the greatest mind to ever contribute to science. He was only 23 years old when he described the laws of motion, and his Earth-shattering works led to the invention of calculus and modern physics. Yet, while Newton's three laws of motion have formed the foundation for non-Einsteinian physics for nearly 300 years, one of them seems to have been both misread and misunderstood.

A 2022 paper from Cambridge University argues that Newton was right all along, yet the most commonly distributed translations of his first law were not. To summarize the claim, the paper points to the common interpretation of Newton's first law to only apply to "force-free bodies." However, according to the research team, the first law is broader and more general than the typical interpretation would suggest.

Newton published his Principia in 1687, which described all three laws of motion. And as was standard for the time, he wrote it in Latin. Consequently, other scholars were tasked with translating the paper into other languages, and the first widely distributed English edition wasn't completed until 1729. That translation, over 40 years after Newton first penned his insights, may have made a nuanced yet important mistake.

Newton's famous first law is widely stated as "a body at rest stays at rest, and a body in motion stays in motion unless acted on by an outside force." While poetically succinct, this statement fails to include a third scenario — that of an object with a force already acting upon it. This is called an object subject to an "impressive force."

The original translation mentions a body at rest and a body in motion, but it doesn't mention an accelerating body — one with an impressive force. Perhaps part of the issue is that "motion" can be ambiguous in meaning, since it's typically understood to refer to constant velocity and not acceleration. Whatever the case may be, it seems we've misread the first law of motion since the inception of its vernacular description.

The crux of the mistranslation surrounds a single word: quatenus. According to the Cambridge paper, this word was incorrectly translated as "unless," when it more accurately means "insofar." Such a minor discrepancy may seem insignificant, but it means that restrictions can be lifted to include massive bodies already subject to impressive forces. In other words, bodies subject to forces can still be acted upon by other forces. So if an object is subjected to the first law, that is, a force, the law stays in play when new forces are introduced. 

The paper proposes a new translation to the first law: "'Every change in a body's state of motion is due to impressed forces," or alternatively: "Bodies only accelerate by force.'" Such a paraphrasing remains faithful to Newton's original Latin description, and it's certainly more accurate to the first law in practice.