Not all constants are equal

[redbird]

This afternoon at work was wrestling with a manuscript, on a level that leaves me thinking that the writer was either unwell, or really distracted, when she wrote the lesson in question. It included a paragraph that, hypothesizing a moon with a circular orbit, explained that the moon's kinetic energy would not change as it moved through its orbit, and neither would its kinetic energy. OK. The paragraph ended "Thus, KE=PE." I went "no, no, no" and realized that I had no idea of what she had meant to say. There were other careless bits in the physics, and a topic omitted that needs to be in there. I spoke to my helpful and sympathetic coworker, Chris; concluded that if we sent the lesson back for rewrite, I'd have to explain what was wrong with it, and between that and the first pass I'd done before finding the physics errors, I would have done most of the work; and sent my boss a note explaining all this and adding that I just wanted her to know that this had happened with this particular book. (The writer in question usually provides basically sound if long-winded copy.) I have fixed the broken physics, and first-drafted three paragraphs to fill the gap.

Then I went to the gym. I'm not, I think, 100% well yet, and two of the machines I like were out of order, but it wasn't a bad workout.

Cardio, 20 minutes plus 2 cooldown, top heart rate 161
(TG) Leg press, 220 pounds, 15; 200 pounds, 2 sets of 15
Chest press, 50 pounds, 12, 7
Wrist curls, 30 pounds, 15; 25 pounds, 15
Calf raise, 70 pounds, 3 sets of 15

Crunches, 3 sets of 30
Back arches, 3 sets of 17
Tree, 5 sets of {3 on each leg}
Balance lateral raise, 3 pounds each hand, 2 sets of 15
Balance squats, 2 sets of 15
Biceps curls, 10 pounds each hand, 20; 7.5 pounds left and 10 pounds right, 20

Stretches

Comments

[brooksmoses]

The paragraph ended "Thus, KE=PE."

I'm guessing that what was intended was "Thus, change in KE = change in PE"?

[redbird]

Possible, but in that paragraph she has just argued that the change in both is 0. So, δKE=δPE is, in the specific case she was describing, true but vacuous.

[brooksmoses]

Right -- I was assuming that it was intended to be an illustration that that general law of orbiting planets holds true in this particular trivial case, as an example.

(I'd agree that, if that's the case, it's not a particularly enlightening one, and more likely to be confusing than helpful.)

[jesse_the_k]

Cheez whiz, you saved generations of students from befuddlement and went to the gym? Outstanding!

[redbird]

That was a good day. Thanks for pointing it out.