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book reviews
Light non-fiction booksreviewed by T. Nelson |
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book reviews
Light non-fiction booksreviewed by T. Nelson |
Reviewed by T. Nelson
If you want to understand anything in modern physics, you have to know about Lagrangians. But what is a Lagrangian, and what does it do?
A Lagrangian is nothing more than the difference between kinetic energy and potential energy (L = T − V). From that simple description of how something changes, you can predict the behavior of almost anything that changes in some way. This book spells it out in detail. There are no skipped steps here and no “it is obvious that”s, but it's not a For Dummies text either. Just a matter-of-fact explanation of what they do and how to use them.
The Lagrangian is usually printed as an upper-case
in Brush or mathcal script.
The main advantage of Lagrangians over Newtonian mechanics is that you no longer need the concept of forces. Instead, as Hirvonen explains, everything is described by energy. This means no more worries about curved coordinate systems or non-inertial accelerating frames. There are no more “fictitious” forces to define and no problems with non-conservative forces like friction. And unlike Newtonian mechanics, Lagrangians can be used to derive conservation laws.
The math is quite easy to follow if you've had calculus and partial differential equations. Hirvonen even explains variational calculus and functionals. Although the formulas sometimes give you a simple numerical answer, often they can only be solved numerically. The real goal in physics, he says, is not to solve the equations, but to find them and gain understanding. After reading this book, you'll be so good at this you'll be creating Euler-Lagrange equations in your sleep.
The main drawback is that the examples showing exactly how to do that are too simple. For example, the see-saw problem of where to place weights on a beam to balance it against gravity is something you can calculate in your head. People would feel embarrassed if they had to define a Lagrangian and derive partial differential equations to solve it, but the author shows it definitely can be done.
This book is from the Profound Physics website, which has many free instructional articles about physics topics as well as some inexpensive courses.
jan 30 2025
This book is neither an in-depth military history nor an in-depth discussion of naval warfare theories. It's for us landlubbers who think US Joint Doctrine is “Don't bogart the reef, man.”
According to Ian Speller, the two greatest naval theorists were Alfred Thayer Mahan, whose basic philosophy was “sink the enemy fleet in a decisive battle”; and Julian Stafford Corbett, who believed that maritime power is only one element and the ultimate focus must be on land. Most subsequent thinkers didn't go into much more depth than this and generally followed one school or the other.
Speller emphasizes that maxims are no substitute for judgment. Some admirals, like Tirpitz, who blindly followed Mahan's principle that an attacker needs one-third superiority in numbers to be successful, led their country into catastrophic failure. The German build-up he advocated only stimulated an arms race with the British and it was the German government's budget, not the enemy, that was sent to the bottom.
Speller says a proven rule is that inferior navies are at more of a disadvantage against stronger navies than inferior armies are against stronger armies. Thus, their strategy is usually harassment and commerce raiding. The French tried this against the British but it failed, in large part because their Revolution killed off many experienced officers. Then there was the Jeune École (young school) theory, which advocated an irregular, asymmetric approach of sinking civilian passengers as well as sailors. This strategy also failed, as it tended to enrage the population. This happened in WWI, where the sinking of RMS Lusitania brought the United States into the war.
Examples include the Sino-Japanese war, Spanish-American War, Russo-Japanese war, World War I (where there was only one big naval battle), and WWII. As for more recent conflicts, Speller says if the Argentinians had been able to conduct effective joint operations, they could have won the 1982 Falklands war. On the other hand, if the British hadn't foolishly decommissioned their only big carrier (the Ark Royal) four years earlier, thereby forcing them to send in civilian ships like the QE2, the war might never have started. He doesn't say this, but this thinking is in line with Sun Tzu, who said the best battle is the one you don't have to fight.
Speller has some good suggestions for books on military history. As for technology, I'd recommend James Genova's Electronic Warfare Signal Processing as a start.
jan 31 2025