Why were Newton's laws of motion discovered so late?

[bhobba]

Well the answer you can more or less figure out when you look at the laws themselves.

Newton's First Law of Motion states that in order for the motion of an object to change, a force must act upon it, a concept generally called inertia.
Newton's Second Law of Motion says F=MA
Newton's Third Law of Motion states that any time a force acts from one object to another, there is an equal force acting back on the original object. If you pull on a rope, therefore, the rope is pulling back on you as well.

Well let's look at them - law 1 follows from law 2 and law 2 is just a definition of force. Law three uses the concept of force and is experimentally testable - so it seems there is just one law. There really isn't, but we will not go into it here. The point of the first 2 laws is to say, when analysing classical mechanics problems etc is - get thee to the forces. That is a very deep observation about nature that is far from obvious. It took a long time to distill it from all the, what was generally little understood phenomena at the time. Only a person of the highest intellect like Newton could do it, and then only after being preceded by other greats like Galileo and inventing a new branch of math - Calculus - although I seem to remember rather than using it in the Principa he preferred ingenious geometrical arguments. Once the concept of force was seen as the correct paradigm then law 3 was not that difficult from everyday experience. The hard part was knowing - get thee to the forces.

Once that was done then mathematicians got a hold of it and developed the equivalent Principle of Least Action formalism - that is the deepest statement of all. Once Noether came along it was seen that using the PLA, symmetry was its real basis. And Feynman (well actually Dirac - but again we will not go into it) showed the PLA follows from QM. So we now know the true basis is QM and symmetry.

Again it took a long time to realize that very deep fact about nature - a lot of water needed to pass under the bridge first - not the least of which was Noether's discovery that stunned even Einstein. When students first encounter it its not uncommon for them just to sit there in awe struck silence as its import sinks in.

Thanks
Bill

 

[sophiecentaur]

1. Infinitesimal calculus.

Newton and Leibniz both developed methods of calculus independently (but not according to Sir Isaac, of course) at around the same time. Iirc, Leibniz's notation was so much easier to use that it is a version of that which we use these days.

 

[Aikiman007]

Leonardo got his inspiration from nature like the spinning seed pod and was able to understand the structure of nature rather than understand the actual physics of air pressure and force. Clearly as shown in history you don't have to understand the nature of force in order to develop a cart with wheels to carry hay, it just works.

 

[sophiecentaur]

Leonardo got his inspiration from nature like the spinning seed pod and was able to understand the structure of nature rather than understand the actual physics of air pressure and force. Clearly as shown in history you don't have to understand the nature of force in order to develop a cart with wheels to carry hay, it just works.

Technology has often been way ahead of the Science which 'explains' what is happening. Steel production was achieved long before modern Chemistry. Etc., Etc..

 

[mark!]

In addition, in Da Vinci's time, 'reason' was only allowed if it didn't contradict the word of the Bible and thus the rule of the aristocracy, who of course had the undoubted mandate from heaven, which Da Vinci's inventions weren't affecting at all. As a matter of fact, he was pretty close with the French King at that time. Newton on the other hand started a whole new view on on the natural world, and the justification of rule itself, because if gravity on Earth could really be the same force which makes the planets orbit in the heavens above, then perhaps this whole God thingy could be wrong. So, people started to doubt the mandate of the church, and 'belief' really started to make way for 'belief'.

The onset of the age of Enlightenment was therefore innovative as well as a rejection of aristocratic rule in general, and the clergy had a hard time imprisoning people like Voltaire who were spreading more and more Enlightenment ideas. Galilei (who appeared between Da Vinci and Newton) was found suspect of heresy of having the opinion that the Sun lies at the centre of the universe, not the Earth, in contrast to Holy Scripture, and was therefore imprisoned. But eventually, reason won. This very important period in history would later be the inspiration for the declaration of independence and the French Revolution.

'Science', and the scientific method, really started with Newton's and his new perspective on the natural world, and unintentionally along with that the justification of aristocratic rule. No longer would truth be something only to be found in the Bible, but rather something that is present right before our eyes, in the material world around us. This was not yet the case with Da Vinci's inventions.

 

[sophiecentaur]

'reason' was only allowed if it didn't contradict the word of the Bible and thus the rule of the aristocracy,

Precisely the situation these days - just in different contexts. Immunisation and climate change are not approved of by many governments. But Science always tends to get the last laugh.
Funny thing, these days, is that the people who deny the parts of Science that suit them will still use all the tools presented to them by modern technology which, of course, hangs on Modern Science. People are odd creatures.

 

[slow]

Archimedes lived centuries before Da Vinci. There is a water pump called Screw of Arquímedes. Basically it is to place inside a pipe a helical screw, whose diameter is slightly smaller than the inside diameter of the pipe. We assume the obligation to use only the vocabulary and practical notions that were available to an educated person in the Da Vinci era.

If the assembly prevents the screw from moving inside the pipe, then the water will move and the system will be used for pumping. If the screw were loose with the pipe full of water, instead of pumping it would travel inside the pipe when it started to turn.

Now think of an Archimedean screw submerged in the water and without the pipe. The screw rotates and the water is displaced perpendicular to the axis of the screw (radial direction). If the turn is fast enough, the volume of water water displaced radially in a time $\Delta t$ will be less than the volume of material of the propeller that tries to push the water to occupy a given region, in that same $\Delta t$. This means that the screw encounters opposition when it rotates in the water, as does an oar. Turning quickly enough, the screw in the water will serve to propel a boat, as the paddle serves. Actually it will serve as a driver in any situation within the water. If the hull of a sunken ship, which is at the bottom of the sea, is fitted with a screw that turns rapidly, the ship could be brought to the surface.

Now let's recognize Da Vinci's mental breadth and knowledge. In the metal workshops of the time bellows were used to propel air and blow the fire of the forge, the furnace, etc. That same bellows propels water when it is submerged in water. The same bellows, used in the same way, do the same in the water and in the air. Could the same thing happen with the screw? That is, if it rotates in the air quickly enough, could it serve as an impeller, just as it does in the water? The air and water are fluid. They differ in density, in viscosity, etc. , but when they are displaced by the helix, they respond in the same way. A properly designed screw, rotating with the proper speed, should serve as an impeller in the open air. This way of reasoning was available to an educated person at that time. And much more within reach of someone as prepared as Da Vinci. To devise his screw-like helicopter did not need to raise what Newton raised later.