When I looked into the history of Charles Coulomb and his famous equation, I found that
even beyond “his” equation, Coulomb was one of the most influential engineers of the 1700s
And his accomplishments are more impressive when you realize that his background was descent
but not considered good enough for the status focused people in charge.
Even worse, his father lost the family fortune, he had a
boss that almost killed him, and he lived through one of the more turbulent times in history
Ready for the story? Let's go!
Before I start the story of Charles Coulomb I have to warn you that I could only
Find two portraits of the man, so I kind of overuse them.
Charles Augustin Coulomb was born in the south of France in 1736 to a middle-class aristocratic family
(his father was a government administrator).
When he was 10 or so, his father got a position in Paris and he started attending the local
school.
However, his lineage wasn’t good enough to be a full-time student (you needed four
generations of noblesse) so he joined as what was called a martinets (or basically auditing
audited the classes).
When he was a bit older, he entered the College royal where he was mistreated for his background
but he had a fantastic math teacher and fell in love with mathematics.
His mother was distraught as she wanted him to be a doctor.
His father, Henry, who was described by a contemporary as “good natured and unsuspecting
[fellow] ” didn’t care but seemed to have a lack of mathematical skills himself as his
father then lost all of the family money in the stock market.
Frustrated, Charles’s mother, Catherine, then kicked his father out and Henry went
back to his hometown of Montpellier.
Catherine, who had money left that she had inherited, tried to blackmail Charles into
becoming a doctor but he rebelled and went to live with his father in Montpellier.
When he was 21, Coulomb joined the Montpellier Society of Sciences which was a small group
of men dedicated to studying mathematics, anatomy, chemistry, botany and physics.
Although the group was impressed with Coulomb’s mathematics skills it didn’t really pay
the bills.
Coulomb had very few options, he could become a priest, or he could join the military as
an engineer.
Coulomb decided on the military and joined a military academy in 1760, when he was 24
years old.
At that school, he took classes in experimental physics from the scientist Abbe Nollet, who
was considered France’s leading electrician ! Anyway, after about a year of instruction,
Coulomb became a lieutenant in the military engineering corp.
After a couple of years doing geological mapping he was transferred to the island of Martinique.
28-year-old Coulomb ended up being a lead engineer designing Fort Bourbon, a 6 million
livre project with 600 workers . Coulomb was a superb engineer and ended up being promoted
to captain after just 6 years of work.
Unfortunately, he also got very ill with a tropical disease and asked his superior named
Le Beuf to let him return to France.
Le Beuf agreed and in 1770 wrote to Versaillles asking for Coulomb to be transferred for the
“future value to the state ”. Then, five days later, Le Beuf had a change of heart
and realized that this would be a good way to get home himself!
He wrote another letter to Versalles saying that he, Le Beuf, was ill and needed to come
home but it was OK as Coulomb could take care of things as Coulomb, “has been in charge
of the work at Fort Bourbon since the beginning, and whom I have decided to keep here for the
next year ”! Poor Coulomb took another 2 years to return to France.
According to a biographer, “Coulomb’s health was so affected by his illness during
the eight-year tour of duty in Martinique that he was never again a well man.
”
Back in France Coulomb wrote on papers on using calculus to optimizing building stability.
The encyclopedia says that his paper of 1773 contains “almost an embarrassment of riches
[including a]… theory of soil mechanics that remains in use today in basic engineering
practice.
”
In 1777, the Paris Academy had a competition to create a very sensitive compass with incredibly
low friction to measure variations in Earth magnetic field during the day as the traditional
compass of a small magnet on a pivot had too much friction to record the variation that
they were looking for.
Coulomb worked on it for a year and co-won the prize for a thin magnet held up by a thin
silk string.
That also inspired Coulomb to work on the physics of friction, which he published in
1781.
An author of a book on friction wrote in 1956 that, “Coulomb’s contribution to the science
of friction were exceptionally great.
Without exaggeration, one can say that he created this science.
”
Anyway, the Paris Academy was impressed with Coulomb’s compass and installed a version
of it at their observatory.
Unfortunately, it turned out to be too sensitive, as a historian put it, the compass “twitched
when an assistant sneezed, or when the door opened, and trembled when carriages passed
the street”.
Coulomb attempted to isolate the needle in a chamber from any drafts but it would still
often move when an assistant touched the outside.
He eventually determined that while walking to the compass, the person who was going to
measure the angle would often gain a little bit of electric charge which would make the
needle sway electrically not magnetically.
Eventually, they grounded the outside of the compass and the needle, which solved the problem.
However, the “twitchy” needle gave Coulomb an idea, maybe he could use a similar setup
to measure the electrostatic force.
One of the difficulties with any study of static electricity is that the forces are
usually so slight that you can only see movement of little pieces of fluff or a feather (or
if wealthy, gold foil).
Most scales and balances cannot measure such minute forces.
Coulomb decided to study the force of twisting (called torsional force).
He wondered if twisting items worked in a similar manner to springs and to what is called
Hooke’s law.
Robert Hooke was an English scientist who lived 100 years earlier in the time of Newton
(in fact Hooke claimed that he had proved that the force of gravity depends on one over
the distance squared before Newton did but didn’t want to share it, claiming that he
would, “conceal it for some time, that others might know how to value it” . Hint: Hooke
never revealed it.)
Some laws he did understand and reveal were about springs.
First, Hooke found that for moderate disturbances, the amount springs compress or stretches is
in direct proportion to the force on the spring.
So, if you double the force, you double the amount the spring stretches, and how much
a spring stretches with a given force depends on the strength of the spring, called the
spring constant.
Therefore, if you know the spring constant, and you know the amount of displacement, then
you can know the force on a spring.
This is how most simple spring scales in people’s bathroom work today.
Hooke also determined that if you pulled a spring and let go it would oscillate up and
down at a steady rate until it stopped.
Therefore, the time for the spring to vibrate back and forth is solely due to the mass on
the spring and the spring constant, not the amount you pull on the mass, which means you
can use the vibration time to determine the spring constant.
Coulomb then took piano wires and twisted them to measure how they vibrated.
He was pleased to find that the wires twisted back and forth isochronously – or at a constant
rate.
This implied that wires twisting follow Hooke’s law – the twist is proportional to the force.
In addition, Coulomb used the time it took for the wire to vibrate back and forth to
measure the “twisting” spring constant.
Then, all Coulomb needed was a bar on a piano wire and the amount it moved would tell him
the force on the bar.
He had just invented the world’s most precise measuring device, where a degree on the scale
was equivalent to 1/100,000th of the weight of a single grain of sand ! Of course, I call
it simple, but the actual experiment was incredibly difficult to complete or recreate, and the
machine was described by a contemporary as an, “all too unsteady twisting machine ”. Still,
the torsion machine was then used for all kinds of scientific experiments (including
by the quirky Englishman Henry Cavendish in 1798 to determine the Gravitational constant
and thus the mass of the Earth).
In fact, torsional balances are *still* used for scientific experiments!
In 1785, Coulomb used his torsional balance on electric charges and experimentally determined
that electrical repulsion force has a force that is proportional to one over the distance
squared confidently writing: “Fundamental law of Electricity: the repulsive force that
the two small balls electrified with the same kind of electricity, follows the inverse proportion
of the square of the distance between the centers of the balls”.
It was a bit more difficult to measure attractive forces but the following year Coulomb determined
that the attractive force of different charges follows the same relationship and that the
electric force was linearly dependent on the size of the charge.
Of course, Coulomb couldn’t directly measure the amount of charge (which is currently measured
in Coulombs).
Instead, he touched a charged ball in the balance with a neutral ball of the same size
and then removed the outside ball to reduce the charge on the ball in the balance by 2,
and found that the force would then also be reduced by 2.
Now Coulomb wasn’t the first person to predict that the electric forces look like gravitational
forces, but he was the first to experimentally validate it and the law is justly named Coulomb’s
law, the constant, Coulomb’s constant, and the value of a charge is measured in Coulombs
in his honor.
Amazingly, Coulomb accomplished all of this while his life was a little, well, chaotic.
In 1783, he was commissioned to determine the feasibility of canal and harbor improvements
in Brittany.
However, when he stated that the plan was ill-conceived, the people hoping to profit
off of the scheme actually had Coulomb imprisoned in jail for his actions ! He ended up being
freed within a week, and having the incident improve his reputation and his standing with
the government.
However, that didn’t help much when the French Revolution began in 1789 and his supporters
were thrown out of power and sometimes, like his friend Lavoisier, lost their heads.
At first, the new leaders were not very happy with a semi-aristocratic scientist like Coulomb,
and by 1791 he quit his position in the military and, for a while, hid in the countryside with
his very young girlfriend Louise and their baby Charles (who was born in 1790).
By 1795, the new leaders had a change of heart and Coulomb was invited back to Paris to be
an Experimental Physicist at the new Institute of France.
In 1802, Coulomb was made the inspector general of public instruction and, with his new important
position, decided to marry Louise and legitimize their now two children (He and Louise had
another son in 1797).
By 1806, Coulomb’s illnesses from his time in Martinique caught up with him and he died
of a “slow fever” at the ripe age of 70.
Thanks for watching, I have a ton of videos about the history of electricity and quantum
mechanics.
I am also making a companion piece about tricks to actually *solve* Coulomb’s problems,
in case you want some math (yum, math).