# If Faraday invented field concept, how did Newton find g?

Tags:
1. Jan 1, 2015

### sawer

This is Newton's law of universal gravitation.
$$F=G\frac{m_1.m_2}{r^2}$$
Gravitational field $$g$$ is derived from this formula

$$g=G\frac{m_1}{r^2}$$ This is named gravitational "field" strength.

If Newton knew nothing about "field concept" and formulated his formula in the form of "action at a distance", how did he interpret $$g$$?

My question is valid for Coulomb as well.

Wasn't this formula
$$E = \frac{Q}{4\pi\varepsilon_{0}r^2}$$
invented by Coulomb?

If so, what did he name for $$E$$?

2. Jan 1, 2015

### jonny23

newton only said that Gravitation force will be proportional to product of mass and inveresly to square of distance..... but he didnot talk about the field which is a contiouous function over space.....

3. Jan 1, 2015

### sawer

Then who found the
$$g=G\frac{m_1}{r^2}$$ ?

If Newton found, what did he call for it besides "field strength"?

4. Jan 1, 2015

### SteamKing

Staff Emeritus
You don't need to have a concept of a field to determine the value of g. You can measure the value of g experimentally. Even the value of G can be determined using a carefully constructed experiment, as Henry Cavendish first did in 1798.

http://en.wikipedia.org/wiki/Gravitational_constant

Similarly, atomic theory originated long before elementary particles like protons, neutrons, or electrons were known.

Things like 'fields' are one way to try to explain what occurs physically and naturally. However convenient the field concept may be, if something better comes along, we might one day regard fields like phlogiston is now regarded in terms of explaining combustion.

The concept of the field was Faraday's intuitive way of explaining how things like electricity and magnetism worked. However, his concept was of little use scientifically until the mathematics of Green and Stokes was developed, which allowed Clerk Maxwell to derive his famous equations of the electromagnetic field.

5. Jan 1, 2015

### sawer

OK. Then What did he name for it?
How can someone measure "field" strength, can't say anything about it?

Newton: "I just measured ____. And it is called ____. It represents ____".
Can you please fill in the blanks without using field keyword?

6. Jan 1, 2015

### OmCheeto

Here's what I think he would have said:

My interpretation is from a translation of his writings, page 81, Newton's Principia : the mathematical principles of natural philosophy (c1846), with a brief life history.

Well that was an interesting read. Did you know, that he was apparently bored with life, and a very bad student, up until, at the age of 12, another schoolboy, kicked him in the stomach. (page 18) And then he became a very good student. I seem to recall something to that effect, that some people just need a swift kick, to get them motivated. But I never knew that about Isaac.

Last edited: Jan 1, 2015
7. Jan 1, 2015

### sawer

No he wouldn't have said that.
g
is not a force.

8. Jan 1, 2015

Staff Emeritus
Not many people, when presented with Newton's own writings, would say "He wouldn't have said that".

9. Jan 1, 2015

### OmCheeto

Ah ha!

As far as I can tell, (600 pages in 2 hours is a bit much for me) he never mentioned g, as other than, a "proportion".
G wouldn't be measured for another 111 years, by Cavendish.

I think he acknowledged this:

So I don't think your original question, as stated, is valid.

But reading the Principia was fun. It's full of all sorts of weird and interesting things: dried pigs bladders, and he used pendulums extensively.
The index starts on page 581 of the translation.

10. Jan 1, 2015

### sophiecentaur

You are ignoring the fact that you are looking backwards to Newton's time. There are many concept that we take for granted these days but they are not necessary for arriving at a 'reasonable' model for things. We can so easily forget that a 'Field' is totally a construct of our mind, which predicts the effect of one thing on another. Within his limits, Newton's model was self consistent - that's what was so clever about it.
But we know that he was not 100% infallible. He got it entirely wrong about Chemistry and believed in the occult and Alchemy. He was also capable of being a very nasty chap to many people.
Our hero was definitely flawed.

11. Jan 1, 2015

### OmCheeto

And he said the gravitational force on the moon was 1/3 of that on Earth. 100% wrong! What a buffoon.
pages 458-459 pdf, 452-453 original copy

12. Jan 1, 2015

### sophiecentaur

Massive fail. Can't win em all, Isaac!