Why did it take 100 years approximately for the idea of energy to be accepted

[cosmic onion]

When we learn about energy and momentum at high school it can be taught by simple equations in a 1 hour lesson. So why did it take over 100 years from approx 1690 to 1790 for energy being direclty proportional to v squared to be accepted by the wider scientific community.

Also shouldn't the answer to this question be taught when learning basic physics.

Soft question does it belong in this part of forum ?

 

[jerromyjon]

When we learn about energy and momentum at high school it can be taught by simple equations in a 1 hour lesson. So why did it take over 100 years from approx 1690 to 1790 for energy being direclty proportional to v squared

I'm not sure what you mean by this, I only know momentum as p=mv.

 

[mishima]

As I understand, Newton, Leibniz, Descartes along with other natural philosophers were interested in developing a fundamental "quantity of motion". This was hundreds of years before the word "science" even existed, and experimentation was still fairly new. Newton and Leibniz' idea was closer to modern kinetic energy while Descartes was closer to modern momentum. So they were sort of debating about 2 different things without realizing it.

 

[cosmic onion]

I imagine answers to this question could fill a small book. It's interesting to me that things that are taught as basic fundamentals of physics sometimes have a long and complicated history.

Thanks for the response

 

[jerromyjon]

basic fundamentals of physics sometimes have a long and complicated history.

The history has some merit but the point is you can learn things easier once they are simplified to fundamental components.

 

[FactChecker]

The history has some merit but the point is you can learn things easier once they are simplified to fundamental components.

Particularly when history took bad turns like Newton's idea that momentum was the same as what we would later call 'energy'. So he thought energy was proportional to v, not v², and he had a lot of influence.

 

[cosmic onion]

I'm glad you mentioned about Newton. This goes to the heart of why I posted the question. Newton was a smart guy (he solved the branchistochrone problem in one night). So why did he get this wrong when Leibniz his contemporary got it right. Imagine the thought experiment. Your in physics 101 and Is sac is siting next to you and the professor derives kinetic energy and momentum as a product of force distant and force time and explains the difference qualitatively using the example of a guy firing a gun with the momentum of the recoil and energy of the speeding bullet. The interesting thing is 'what's Newtons response'. I think we could all learn a lot from his response. It would be an interesting lecture.

 

[jerromyjon]

The interesting thing is 'what's Newtons response'.

* makes up new quote * "If I have shot further it is because I had a giant behind me holding the gun!"

 

[I like Serena]

I'm glad you mentioned about Newton. This goes to the heart of why I posted the question. Newton was a smart guy (he solved the branchistochrone problem in one night). So why did he get this wrong when Leibniz his contemporary got it right. Imagine the thought experiment. Your in physics 101 and Is sac is siting next to you and the professor derives kinetic energy and momentum as a product of force distant and force time and explains the difference qualitatively using the example of a guy firing a gun with the momentum of the recoil and energy of the speeding bullet. The interesting thing is 'what's Newtons response'. I think we could all learn a lot from his response. It would be an interesting lecture.

It would likely be a lecture where people are endlessly confusing what the words momentum and energy are supposed to mean.
And at the same time Newton would probably know exactly that he would need 4 times as much gunpowder to project a bullet 2 times as fast.
I doubt either got it wrong - it's just a struggle to find words for what needs to be expressed, and settling on something that all parties can agree on.

 

[FactChecker]

Newton knew about momentum, which so successfully explained so many things. It clearly was conserved and transferred energy from one object to another. So I imagine he was reluctant to realize that something else was needed. It would take systematic measurements of energy in the form of joules to really prove that something fundamentally new was needed, proportional to v².

 

[cosmic onion]

We had to wait for Joule to tell us by experiment that Leibniz was correct ?

 

[jerromyjon]

We had to wait for Joule to tell us by experiment that Leibniz was correct ?

Or understand it by ourselves... if you need a teacher to tell you are right then you are merely learning by example. History says you can figure it out by yourself...

 

[FactChecker]

We had to wait for Joule to tell us by experiment that Leibniz was correct ?

I don't know. I'm not good at the history of physics, so I should not be speculating as much as I have here.

 

[David Lewis]

It would take systematic measurements of energy in the form of joules to really prove that something fundamentally new was needed, proportional to v2.

You're close. Newton wrongly believed energy was proportional to quantity of motion (i.e. momentum). Following up Leibniz' ideas, however, the French physicist Du Châtelet dropped balls into clay, measured the depth of the impressions, and discovered kinetic energy was proportional to the square of velocity.

 

[FactChecker]

You're close. Newton wrongly believed energy was proportional to quantity of motion (i.e. momentum). Following up Leibniz' ideas, however, the French physicist Du Châtelet dropped balls into clay, measured the depth of the impressions, and discovered kinetic energy was proportional to the square of velocity.

I remember now seeing discussion of Émilie Du Châtelet in the Nova TV show Einstein's Big Idea (it's on youtube). She was a fascinating woman. @cosmic onion may be interested in watching that show and in reading https://en.wikipedia.org/wiki/Émilie_du_Châtelet#Advocacy_of_kinetic_energy

 

[jerromyjon]

the French physicist Du Châtelet dropped balls into clay, measured the depth of the impressions, and discovered kinetic energy was proportional to the square of velocity.

That's where the E_k=1/2mv² comes from but I'm curious... doesn't that include the gravitational force as well as the kinetic energy? For example if you place a bowling ball on soft clay with no velocity then a dent will form from it's mass...

 

[jbriggs444]

That's where the E_k=1/2mv² comes from but I'm curious... doesn't that include the gravitational force as well as the kinetic energy? For example if you place a bowling ball on soft clay with no velocity then a dent will form from it's mass...

For a given object, a dent from static gravitation would be smaller than a dent from impact. In addition, it would be possible to control the experiment to reduce the effect of the static gravitational dent -- subtract the known depth of a gravitational dent from the measured depth of the impact dent.

 

[sophiecentaur]

Or understand it by ourselves... if you need a teacher to tell you are right then you are merely learning by example. History says you can figure it out by yourself...

"yourself"? It often requires a remarkable "yourself" to figure out the big steps in Science ( and other learning). When you are presented with the full argument for a phenomenon it can appear blindingly obvious but that's post hoc. I think you undervalue the special abilities of our great thinkers.

 

[FactChecker]

Unless he is a genius, a person who tries to figure everything out by himself is doomed to a life of muddled, confusing thoughts. There is great beauty in the theories of geniuses of the past and in the combined hard work of the millions down through history. If a person only wants to show off his own capabilities, he should stick to silly puzzles. If he wants to understand the beauty of the physical world, he should learn from the greats.

 

[ftr]

with the advent of QM and relativity, this question is still there because E^2=(pc)^2 +m^2c^4. But modern physics does not care about what things are called only that the equations work.

 

[David Lewis]

...if you place a bowling ball on soft clay with no velocity then a dent will form from its mass...

No worries. If a significant indentation forms just from the expenditure of potential energy, the clay is probably too soft to obtain good results.

 

[cosmic onion]

I have never been happy with the word genius. I always thought that genius is like entrepreneur a person who happens to be in the right place at the right time doing the right thing in the right way with the right support and motivation. When all these things come together then new discoveries are made or businesses thrive. I think all discoveries are products of there time. If no Einstein then someone else.

 

[FactChecker]

I have never been happy with the word genius. I always thought that genius is like entrepreneur a person who happens to be in the right place at the right time doing the right thing in the right way with the right support and motivation. When all these things come together then new discoveries are made or businesses thrive. I think all discoveries are products of there time. If no Einstein then someone else.

In that case the "someone else" would have to be a genius. Einstein did many things that were breakthroughs in different areas. His work on General Relativity was an extremely unusual combination of clear thought, determination, long, hard work, and egotistical confidence.

 

[FactChecker]

I have never been happy with the word genius. I always thought that genius is like entrepreneur a person who happens to be in the right place at the right time doing the right thing in the right way with the right support and motivation. When all these things come together then new discoveries are made or businesses thrive. I think all discoveries are products of there time. If no Einstein then someone else.

Not really. The proof is that few people now, many decades later, can understand theories like General Relativity or Quantum Theory even after they have been clarified, simplified, reworked, and explained from many directions.

 

[OmCheeto]

modern physics does not care about what things are called only that the equations work.

This is why, after reading Factcheckers reference, I did some maths.

Émilie_du_Châtelet#Advocacy_of_kinetic_energy

"Simply put, there is no 'momentum friction' and momentum can not transfer between different forms, and particularly there is no potential momentum. Emmy Noether proved this to be true for all problems where the initial state is symmetric in generalized coordinates."​

Looking at some simple equations:

ke = 1/2 m v^2
pe = mgh
p = mv​

It seems to me that momentum can be derived from either of the two energy equations.

√(2*mass*ke) = p(kinetic)
√(2*mass*pe) = p(potential)​

So the part I bolded struck me as incorrect.
Though, it may be correct in the full context of the statement, as I'm not sure what is meant by "the initial state is symmetric in generalized coordinates"

But anyways, this took me back to the original question:

So why did it take over 100 years from approx 1690 to 1790 for energy being direclty proportional to v squared to be accepted by the wider scientific community.

My guess, is clocks.
Going through the history of timekeeping in wikipedia, I discovered that Huygen's made the first accurate clock. And it was a pendulum clock. Now I've done pendulum experiments before, but I've never used a pendulum as a timekeeping device.

So I googled further, and found:

Christiaan Huygens & The Pendulum Clock by TimeCenter.com

"Until the quartz clock was invented in 1927, the pendulum clock reigned as the most accurate measurement of time for two hundred and seventy years."​

Now, I've obviously left out a couple of hundred years of scientific history, as by 1790, someone obviously figured out how to measure speed accurately enough to determine that it was v², and not v.

And that, is my final answer: Clocks

 

[jerromyjon]

"yourself"? It often requires a remarkable "yourself" to figure out the big steps in Science ( and other learning). When you are presented with the full argument for a phenomenon it can appear blindingly obvious but that's post hoc. I think you undervalue the special abilities of our great thinkers.

I think you are taking it further than I intended to convey. The point I was making is that with the accessibility of tools and materials these days it is very easy to do your own experiments and obtain your own results and conclude scientific facts on your own. "Great thinkers" wouldn't know their abilities without ambition to try and confidence in their conclusions...

 

[NTL2009]

... My guess, is clocks. ...

Now, I've obviously left out a couple of hundred years of scientific history, as by 1790, someone obviously figured out how to measure speed accurately enough to determine that it was v², and not v.

And that, is my final answer: Clocks

But I think it is fairly easy to set up experiments where one object is at 2x and 4x the velocity of another object, w/o absolute timekeeping. You could set up ramps for balls to roll down to a flat section such that by observation (balls all cross an 'entry' line at the same time, and lines marked each meter), the balls covered 1 Meter, 2 Meters and 4 Meters over the same time.

A disk with balls attached at a radius of 1 Meter, 2 Meters and 4 Meters, and a mechanism to release those balls, or drop an object into their path and measure the force (like with the clay impression example above), would provide those velocities.

 

[FactChecker]

Now, I've obviously left out a couple of hundred years of scientific history, as by 1790, someone obviously figured out how to measure speed accurately enough to determine that it was v², and not v.

Newton knew what velocities occurred due to the acceleration of gravity. They were obsessed with the motion of planets (and cannonballs) and so that was the first thing they figured out. The real breakthrough was the experiment of dropping a ball into clay and measuring the impact dent. That showed that there was something fundamental (energy) which varied proportional to v².

 

[sophiecentaur]

obtain your own results and conclude scientific facts on your own

I think you underestimate the serious paradigm changes over the years and the immense leaps in understanding that have been achieved. I do not know - you may be a genius - but your average to very bright student would not get far with no input from books or teachers.
IF you want to prove me wrong then just try to derive the Planck radiation curve from what you already know (and no peeking in a book!)

 

[anorlunda]

One thing should have been evident even without accurate experiments, is that momentum is signed, but K.E. Is always positive.

It takes the same gunpowder (energy) to shoot a cannonball east or west.

When two objects collide and exchange momentum it makes a world of difference if the were traveling in the same or opposite directions.

That is a clue that momentum should be proportional to an odd power of v and energy to an even power of v.