# Newton's First Law -- Mistranslated for 3 centuries

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• jedishrfu
jedishrfu
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TL;DR Summary
A subtle mistranslation of Isaac Newton’s first law of motion that flew under the radar for three centuries is giving new insight into what the pioneering natural philosopher was thinking when he laid the foundations of classical mechanics.

This difference might seem rather academic.
I cannot agree more. Newton's law as we know it is, given ##F=m\cdot \ddot x,##
$$F=0 \Longleftrightarrow \dot v=\ddot x =0$$
and DiSalle wants us to believe Newton meant to say
$$F\neq 0 \Longleftrightarrow \dot v=\ddot x \neq 0$$
That is not worth noting. I am sure that Newton was aware of the equivalence. I wish DiSalle had quoted properly and referenced the exact location in Newton's original work - in Latin - so I could look it up.

Venturi365, Klystron, vanhees71 and 1 other person
Well, we seem to have gotten on alright in the intervening 300 years... I have sensed no non-local changes in physics due to this discovery. But it is interesting from a history of physics point of view.

PeroK and vanhees71
Philosophers...

hutchphd, PeroK, Haborix and 1 other person
vanhees71 said:
Philosophers...
You remind me of the group of people who are always yelling at the unemployed to get a job

weirdoguy
The first law was Galileo's anyway. Galileo did experiments with balls rolling down and then up inclined ramps separated by flat surfaces and noticed that the ball would roll down one and up to about the same height on the distant one regardless of how far apart they were. He concluded that:
"An object, if once set in motion, moves with uniform velocity if no force acts on it."

Galileo knew about gravity and, in fact, did experiments to show that the rate of fall was independent of mass. But a ball rolling on a smooth level surface is not affected by a net force of gravity. Gravity only applied a net force if the surface was inclined.

As far as the "mis-translation" of Newton's statement of the first law is concerned, decide for yourself:

Law 1
Every body should persist in its state of rest or of moving uniformly in a straight direction, except in so far as it is forced to change its state by impressed forces.
Projectiles continue in their motions, except in so far as they are retarded by the resistance of the air, and are driven downwards by the force of gravity. A little piece, the parts of which are continually retracting from rectilinear motions, does not cease to rotate except in so far as it is retarded by the air. But the larger bodies of the planets and comets retain their progressive and circular motions longer in spaces of less resistance.​

AM

syfry, Lnewqban, dextercioby and 3 others
It looks like the philosophers quoted in the OP suffer from the same missunderstanding as many intro physics students: they confuse "force" with "net force". For them a body moving uniformly in a straight line is an imaginary situation. After all, the force is always with you.

PeroK and vanhees71
nasu said:
It looks like the philosophers quoted in the OP suffer from the same missunderstanding as many intro physics students: they confuse "force" with "net force". For them a body moving uniformly in a straight line is an imaginary situation. After all, the force is always with you.
It's not just that. Inertial reference frames, flat spacetime, point masses, continuous mass densities and a whole bunch of other fundamental building blocks of physics are imaginary, idealised scenarios.

IMO, the whole point of Newton's first law was to contradict the perceived wisdom that bodies on Earth naturally slow down without any external agency; and that bodies in the heavens obey a different law (or are powered by the hand of god). It's logically irrelevant how you state this.

sophiecentaur
PeroK said:
IMO, the whole point of Newton's first law was to contradict the perceived wisdom that bodies on Earth naturally slow down without any external agency; and that bodies in the heavens obey a different law (or are powered by the hand of god).
Feynman had an amusing take on the motion of planets:

"...what makes planets go around the sun? At at the time of Kepler, some people answered this problem by saying that there were angels behind here [pointing to the side of the planet nearest the Sun] beating their wings and pushing the planets [outward from the Sun] around an orbit. As we'll see, that answer is not very far from the truth. The only difference is that the angels sit in a different direction [pointing to the side of the planet away from the sun], and their wings go this way [inward, toward the Sun]."​
Feynman - The Character of Physical Law - Cornell Lectures 1965​

AM

Last edited:
hutchphd and vanhees71
PeroK said:
IMO, the whole point of Newton's first law was to contradict the perceived wisdom that bodies on Earth naturally slow down without any external agency
The shadow of Aristotle was difficult to counter. I think that was indeed the intent. No ongoing motive force required.

vanhees71
Andrew Mason said:

Law 1
Every body should persist in its state of rest or of moving uniformly in a straight direction
Wonder if he had realized at the time how really identical those are? Like did Galileo's relativity treat the concepts of 'at rest' and 'uniform motion and direction' as the same thing? Otherwise Newton might've instead have written: "Every motion should persist in its state of uniformity and direction". (whether its frame of reference is at rest or moving)

But the larger bodies of the planets and comets retain their progressive and circular motions longer in spaces of less resistance.​

That too is curious. Wonder if people in his time knew that outer space is a vacuum or nearly so?

Galileo did experiments with balls rolling down and then up inclined ramps separated by flat surfaces and noticed that the ball would roll down one and up to about the same height on the distant one regardless of how far apart they were. He concluded that:
"An object, if once set in motion, moves with uniform velocity if no force acts on it."
Had thought Newton discovered that! So did Newton merely add acceleration as the means to change the uniform velocity, or did he add in only the equation? (or both)

## What is Newton's First Law?

Newton's First Law, often referred to as the law of inertia, states that an object at rest will stay at rest, and an object in motion will stay in motion with the same speed and in the same direction unless acted upon by an unbalanced external force.

## How has Newton's First Law been mistranslated?

The common mistranslation of Newton's First Law lies in the interpretation of the term "uniform motion." Historically, this has often been misunderstood as motion in a straight line at constant speed, but Newton's original text suggests a broader concept of maintaining a state of motion or rest unless influenced by an external force.

## What are the implications of this mistranslation?

This mistranslation can lead to a limited understanding of the law, potentially overlooking the nuances of how forces interact with objects. It might also affect the teaching and application of classical mechanics by oversimplifying the concept of inertia.

## How was the mistranslation discovered?

The mistranslation was discovered through a detailed re-examination of Newton's original Latin text and historical context by modern historians and physicists, who noted discrepancies between the original wording and common interpretations.

## What should be the correct interpretation of Newton's First Law?

The correct interpretation of Newton's First Law should emphasize that an object's state of motion or rest remains unchanged unless acted upon by an external force, without restricting this to linear motion. This interpretation aligns more closely with Newton's original intent and the broader concept of inertia.

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