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On 2003-02-06 17:19, mik sawicki wrote:
I spotted some minor problems that I think might need Phil's attention.
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Interesting reading. I agree with a lot of them, at least on first reading. Some of them have been discussed in other threads, I'll see if I can dig them up.
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2. Page 23, third line from the bottom:
"Lets say you are driving a car north at 100 kph (60 mph) in Wiscasset, Maine. The Coriolis effect deflects you…"
A car is not a good example, as the minute Coriolis acceleration there (0.0014 m/s^2) translates for a 1000 kg car into a Coriolis force of 1.4 N (about 0.3 lb). This force can't deflect the car to the right, since it is too small to overcome the sideways force of static friction between tires and the road, that prevents the tires from skidding sideways. This frictional force will easily peak to the value of some 5,000 N -10,000 N before onset of skidding (on a dry roadway).
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It's not necessary to get anywhere near the 5000 N before the car is deflected. A gentle wind from the side will cause you to steer into it.
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3. Page 23, bottom line, continuation of the same sentence:
"…by the teeny amount of 3 millimeters"
According to my calculations, it's about 0.7 mm, even more teeny.
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My back of the envelope calculation gave 2 mm, so who knows?
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4. Page 24, second line, continuation:
"10 meters (33 feet)"
I got 9 km (kilometers), i.e. about 1000 times more, a reasonable result
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I think the 10 meters was just an extrapolation of the 3mm/second times an hour, which does give around 10 meters. If your figure was even more teeny than that, how'd did you get 1000 times more?
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9. Page 44.
The problem is with the picture. Perhaps a footnote is needed, explaining that the thickness of the atmosphere is vastly exaggerated in comparison to the Earth's size. (Earth appears to have a radius of 1.25 inch, so the atmosphere (troposphere) should be about 0.003 inch thin!
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The vertical is often exaggerated in illustrations--otherwise the diagram would be unreadable. Of course, that's one of the reasons that people imagine a huge cliff at the edge of the continental shelf.
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15. Page 70, line 12 from top:
"The time of high and low tides changes every day by about a half hour"
Your explanation and calculation are correct, but the wording of the conclusion is a bit confusing. I'd say the morning tide tomorrow will be about 50 minutes later than the morning tide today, etc.
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I remember this one, we hashed it out in
Bad "Bad Astronomy: Misconceptions"