Factory Physics is a fascinating look into the math and science behind factories and production lines. It begins with a history of scientific management — covering the transition from departments centered around processes to lines focused on products, from planning-based systems like material requirements planning (MRP) that batch and release jobs onto the factory floor, to new theories of factory management like lean manufacturing, the Toyota Production System, Kanban. It explains why these various approaches can fail in surprising and unintuitive ways because they often emphasize high-level subjective goals like the elimination of waste or high utilization, and states that we need to understand the lower-level math of how individual machines, production and assembly lines work.

Every manufacturing system involves 1. stocks (raw materials, work in progress inventory, and finished goods inventory) and 2. flows (transformation steps like movement or manufacturing processes)

The bottleneck rate r_B = throughput / capacity Work in Progress = Bottleneck rate * Longest Cycle Time

The book then covers how you can trade off inventory, time, or capacity in a manufacturing system, but sometimes have constraints on one or the other.

Variability — both process variability due to intrinsic variation and planned or unplanned downtime and inter-arrival variability which is determined by the amount of batching and the transport system between steps — is a source of evil in a manufacturing system, and leads to super-linear growth in the amount of inventory, time, or capacity needed to pay for or cover the variability.

While reading the book I realized that lean manufacturing/Toyota-inspired principles seem to fall naturally out of the natural laws or axioms they describe. Because variability leads to inefficiency, and variability is only visible with low inventory/WIP levels, we should aim to reduce WIP. This also means reducing rework.

They also state “When demand is steady, the product mix is constant, and processes are well behaved, almost any type of system (e.g., reorder points, MRP, or kanban) can work well, as shown by the simulation studies of Krajewski et al. (1987).” Thus for a startup trying to scale up manufacturing of only a few products, with pre-orders providing a backlog of stable demand, many of the advanced methods can be eschewed for a focus on they key principles including variability, queueing, and bottlenecks. This allows for much simpler planning and execution modeling/tools.

Employees regress to the mean just like any other natural phenomenon. While there may be some distribution over their natural abilities, individual performances may vary significantly, and the “best employees” will tend to get worse and “worst” tend to get better relative to their intrinsic means over time.

Add a lot of charts

Jet engines article Compressor and electric motor efficiency maps Thermodynamic models - differential equations connected to eachother

• Rome wasn’t built in a day.

The Alchemy of Air

Nitrogen makes plants grow, guns fire, and munitions explode. But for much of history it has been locked up in the air, in a chemical arrangement (dinitrogen, or N2) so strong it can only be split naturally by lightning. So humans shoveled manure, horse poop, guano bird excrement, and dug saltpeter from the Atacama desert to fertilize fields across the globe. Fertilizers became a gold rush for the nations, laborers, shippers that moved millions of tons of it each year. In 1900, scientists estimated that the natural supply of nitrogen would disappear by 1920, leading to mass starvation and death. So they began working on synthetic nitrogen, either via electric lightning, or by a new process that used the highest temperatures and pressures of any chemical reaction known to science.

The characters in this story are Fritz Haber, a Jew who wanted desparately to be an esteemed German, and who neglected two wives, shunned other Jews, and built chemical weapons in pursuit of this dream, only to have it shattered by the Nazis who promptly pushed him out of his position as head of a state research institute. And then there is Carl Bosch, a machinist and metallurgist who turned Haber’s ideas into a machine, a machine into a factory, and then a multiple factories into windfall profits for BASF, the company he came to lead, and the source of gunpowder, explosives, and gasoline for Nazi war machine.

who pivoted its profits from dyes to fertilizer with the machine he built, and who ended up leading the entire company to become the machine that supplied the Nazis