Physics! #2: University Physics 1.2

Section 1.2: Solving Physics Problems

One of the things I love about physics is the insistence on math. I remember a while back, a person posted to /physics asking for a book that’d teach him QM without any math. Unfortunately, I think a lot of people think this way. I think it’s a symptom of a more general problem – most people don’t connect math with logic. But, of course, math is just a very tall tower of logic, and if you want to see all of physics, you’re going to have to climb pretty high in the tower.

The book does a solid job of explaining how to solve physics problems as I understand it. They say: “Identify, Set Up, Execute, Evaluate. To me, the big trick with physics problems is that first step. Physics problems have the often tricky combination of logic puzzles and hard math. So, it’s important to know the pieces you’re working with (equations, facts) and the operations that are available (what’s logically legal according to the problem). I find I and others have the most trouble with physics problems when we attempt to dive in without taking stock of the available information.

Of course, they actually left out a few crucial steps. It should go: “Identify, Set Up, Execute, Fail, Frustration, Second Attempt, Anger, Go Home, Explain Problem to Friend, Find Solution is Obvious, Evaluate, Feel Stupid.”

The second part of section 1.2 deals with the physics idea of idealized models. As many of you know, idealized models are the butt of many jokes in physics, of the sort “Imagine a penis as a sphere constantly ejaculating in every direction, with an average flux of Φ.” Or, as my mechanics professor once said, “We physicists live in an ideal world.”

I don’t have anything new to say about idealizations, so I’ll refrain. I think we’re all aware of the benefits and pitfalls of idealized physics.

Wow, these first few sections are going pretty fast. I’ll remember this fondly when I’m knee deep in cross products…

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6 Responses to Physics! #2: University Physics 1.2

  1. Morris Keesan says:

    My favorite is “Imagine a spherical cow …”, but I don’t remember the setup to that punchline.

  2. William says:

    I love your description of how to solve physics problems. It really took me back to my undergraduate physics class and even my graduate level cs algorithms class last year. Fun stuff. :-)

  3. I recall taking an EE course a long time ago. The professor was fairly humorless, a Brit, also fairly imperturbable, so our goal was to try and get him to smile or at least get a rise out of him.
    My attempt was, after his lecture on Kirchhoff’s law, and the definition of Siemens, I raised my hand:

    “So, to summarize, if you apply Jerkoffs law, you get semen?”

    Class cracks up… professor looks at me, presses his glasses up the bridge of his nose and in his British accent:
    “No.”

    Not a smile, not a frown… his reaction was quite rectified.

    Oh well.

  4. Paul says:

    Yo Zach, just started reading these after Wire linked to them. Nice! Having gone through an undergraduate physics education long ago, I will tell you that “Imagine a penis as a sphere constantly ejaculating in every direction, with an average flux of Φ.” is the greatest example of the idealizations involved in intro physics I have ever heard. Keep it up.

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