A hockey puck sliding on ice moves uniformly in a straight line, except insofar as resistance from the ice and air slows it down. Hoek gave a real-world example of the first law. The new wording, unlike the old, does not suggest that bodies untouched by external forces exist.Ī good paraphrase, according to Hoek, would be: “Every change in a body’s state of motion is due to forces impressed from the outside.” The difference between Cohen/Whitman’s “except insofar” and Motte’s “unless” isn’t trivial, says Hoek, who specializes in the philosophy of language. ![]() “Every body perseveres in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by the forces impressed.” (“Forces impressed” means the forces pressing or acting on the body.) It fell to Hoek, years later, to point out how the new wording - truer to Newton’s original - clears up a centuries-old misunderstanding of what Newton meant. This 1999 work listed a number of mistakes in the Motte edition but did not call special attention to the first law. Bernard Cohen and Anne Whitman, the first in more than 285 years. ![]() There he discovered that “Principia” was available in a newer translation by I. So the idea that he overlooked this struck me as very implausible.”Īround 2011, Hoek went to the library at Oxford’s Worcester College. This is like, the words in the first law. “I thought, surely people can’t be right that Newton overlooked something like that, because especially by the time I was taking these philosophy of physics classes, I was very impressed that Newton is a very philosophically careful person who really thinks about his words very, very carefully. ![]() The issue continued to bother Hoek as an undergraduate at the University of Oxford, where he was studying math and philosophy. (If you happen to run across a first edition of Motte’s version - mistranslation and all - at a yard sale, make an offer anyway. “So physicists don’t necessarily get access to the original version,” Hoek said, although they “maybe realized that something was a little bit odd.” In reality, all bodies are acted upon by gravity and other forces like friction.īut for hundreds of years, textbooks copied Motte’s translation. The “unless” seems to imply that there are at least some bodies not subject to external forces. “Every body perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impress’d thereon.” In 1729, Andrew Motte published his English translation of “Principia.” Newton, having died in 1727, was not available to review it. If you wanted to say it really right, you needed to use Latin.”īut not everyone reads Latin. “Newton was writing for his fellow scientists in France and Germany.” Also there was “a perception at the time that Latin … was the language of science. “At the time, English was not the language of science, the way it is now,” Hoek said. Image courtesy of the Isaac Newton Institute. Isaac Newton, as painted by Godfrey Kneller. ![]() Newton has taken some heat over the centuries from critics including physicist Sir Arthur Eddington, who, with tongue in cheek, rephrased the famous maxim as “Every body continues in its state of rest or uniform motion in a straight line, except insofar as it doesn’t.”Ī modern wag might say, “Newton is the author of the law of inertia, except that he isn’t.” At least he didn’t say it the way many students have learned it, according to Hoek.įirst of all, Newton wrote it in Latin, not English. “But I always thought that’s still strange, to make your first law of one of the most famous principles of physics about these imaginary bodies.” In other words, why bother to make a law - and make it the first law - about bodies that don’t exist? I think I actually talked to my teacher about that at the time and he said, ‘Well, the law says that if there were a body that wasn’t subject to forces, then it would go in a straight line. “And then, at some point, you think, ‘Well, then, what does this law do? When does an object move in a straight line?’ It turns out that actually … never, at least never in the actual world. It doesn’t go in a straight line because the earth’s gravity is pulling on it. In fact, something about the first law has bothered Hoek since he was a high school student who took physics - as well as Latin - in his hometown of Utrecht in the Netherlands. It’s that word “unless” that bothered Hoek, who, as a philosopher, is attuned to fine shades of meaning.
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