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 around 10 years old, his father got a job in Paris, and Coulomb 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 instead he became what was called a martinet, or audited the classes, when he was a bit older, he entered the College Royal, where he was mistreated a bit for his background, but he had a fantastic math teacher and fell in love with maths. His mother was distraught, as she wanted him to be a doctor, but his father, who was described by a contemporary as a good-natured and unsuspecting fellow, didn’t seem to care, but also seemed to have a lack of mathematical skills himself, as his father then lost all the family money in the stock market.
Legitimately frustrated, Coulomb’s mother, Catherine, kicked Coulomb’s father, Henry, out of the house, and Henry went back to his hometown of Montpellier. Coulomb’s mother, who still had some money left that she had inherited, tried to blackmail Charles into becoming a doctor, but he rebelled and left Paris and went to live with his father in Montpellier. He didn’t have very many options, he could join the priesthood, 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. Coulomb was a superb engineer, and ended up being promoted to captain after only six years of work.
Unfortunately, he also got very ill with a tropical disease, and asked his superior, named Leboeuf, to let him be transferred back to France for his own health. Leboeuf agreed, and in 1770 wrote to Versailles asking for Coulomb to be transferred home for his, quote, “Future value to the state.” But it was okay, as Coulomb could take care of things, as Coulomb, quote, “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.” This inspired him to start working on the physics of friction, which he published in 1781.
Coulomb attempted to isolate the needle in a chamber free from any drafts, but it would still often move when the assistant touched the outside. Coulomb eventually figured out that the person walking to the compass would often gain a little bit of electric charge, which would then make the needle sway electrically. Eventually, they grounded the needle and the outside and the person, and it seemed to solve the problem. However, the twitching needle gave Coulomb an idea. Maybe he could use the twisting force to study the electrostatic force. See, the problem with studying static electricity is that usually, the forces are so slight that you can only see movements of little pieces of fluff or feather, or if wealthy, gold foil. Most scales cannot measure such minute forces.
Coulomb decided to study the force of twisting, called the torsional force. He wondered if twisting items worked in a similar manner to springs in what is called Hooke’s law. Robert Hooke was a scientist who lived 100 years before Coulomb, in the time of Newton. Fun fact, Hooke claimed that he had proved that the force of gravity depends on one over the distance squared before Newton did. Hint, Hooke never revealed it. Some laws Hooke did reveal and understand were about springs. First, Hooke found that for moderate disturbances, the amount springs compress or stretches is 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 the spring is displaced, then you can know the force on the spring. This is how most simple spring scales work in like, a grocery store today. It also means you can use the spring’s vibration time to determine the spring constant. Coulomb then took piano wires and twisted them to measure how they vibrate, he was pleased to find that the wires twisted back and forth at a constant rate. This implies that twisting follows Hooke’s law, that 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 and a piano wire, and the amount it moved would tell him the force.
Coulomb had just invented the world’s most precise measuring device, where a degree on the scale was equivalent to the weight of 1/100,000 of a single grain of sand. Of course, I call it simple, but the actual experiment was incredibly difficult, and the machine was described by a contemporary as an all too unsteady twisting machine. Still, the torsion scale was used for all kinds of scientific experiments, in fact, torsional balances are still used for scientific experiments.Amazingly, Coulomb accomplished all of this when his life was kind of chaotic.
In 1783, Coulomb was commissioned to determine the feasibility of canal and harbor improvements in Brittany, however, when he determined that the plan was ill-conceived, the people hoping to profit off the scheme actually had Coulomb placed in jail for his opinions, he ended up being freed within a week, and for a while, the incident actually improved his standing with the people in government, but that didn’t help much in 1789 when the French Revolution began and his mentors were thrown out of power, and sometimes, like his friend Lavoisier, got angry.
By 1795, the new leaders had a change of heart and invited him back to Paris to be one of the first experimental physicists at the New Institute of France. By 1802, Charles Coulomb was made the inspector general of the public schools, and with this new important position, he decided to marry Louise and legitimize their now two children, however, 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. He’s been honored by France ever since, in fact, 83 years after his death, Gustave Eiffel had Coulomb’s name engraved on the side of the Eiffel Tower.