"You are quite right that strictly speaking the time Superman must
spend pushing off from the ground is closer to 20 - 30 milliseconds, 
rather than the longer 0.25 seconds used in my book.
I went with the longer time for two reasons:

(1)  Experiments with the students in my class over the years seemed to 
support the 1/4 second time,  and more importantly

(2)  I'm NOT actually trying to account for Superman's powers (which 
are clearly unphysical) but simpy trying to illustrate how acceleration 
is obtained from a change of speed in a given time period.  For the 
results in the second chapter, I would like this acceleration,
and hence the accompanying force, to be as low as possible, for its 
implications about the gravity on Krypton.  

If I used 25 msec for the time spent leaping, and then concluded that 
Krypton's gravity is 150 times larger than Earth's, one would not be 
surprised that such a planet could not be constructed. 
But 15 times Earth's gravity seems like it should be do-able - but 
even this relatively modest increase in gravity is hard to physically 
realize.  Thus, purely on pedagogic grounds, I have a vested interest
in keeping the time spent leaping as long as I can get away with.

After all, the purpose of the book is to try to explain physics in a fun 
and accessible manner, and NOT to provide "scientific explanations" for 
superpowers.  Clearly they are impossible.   And one thing you stated 
in the blog is not quite right - the book is not intended as a textbook, 
but as a popular science book for the general reader.  Most of the 
readers are not as adept in physics as you are - and I would expect 
that they would be bored with the level of physics I employ.

The discrepancy you bring up - 0.25 seconds vs 0.025 seconds - has been
caught by others.  One reader, arguing back and forth with me, finally 
said: "It'sjust not realistic that the time would be that long!"  At 
which point I replied:

"We are discussing the last son of the doomed planet Krypton, and his 
leaping a 30 story building in a single bound - and the time he spends 
jumping is the most unrealistic aspect of the problem?"

At which point he laughingly conceded.  

So - yes, technically - you are correct regarding the time to leap - but
then it spoils my discussion of Krypton.  Consequently I, as a long time 
comic book fan, choose to continue to suspend disbelief, and extend 
Superman's "miracle exception."  I still believe that a man can fly - 
by pushing off from the ground in 1/4 of a second!

Cheers,
Your Friendly Neighborhood Physics Professor,
Jim Kakalios"

Friday feedback, funnies and 'fessups

Here are some of the comments, etc. you sent this week. First off, a big Thankyou to blogreader Helen Babby of California, USA, who knows that I am a keen motorcyclist. Helen sent me inter alia the sheet of US stamps showing American motorcycles which I display below. Left to right in the top row :-

• a 1940 Indian Four. The 1940 entry in a series of deluxe, 4-cylinder motorcycles featured skirted fenders that partially covered the wheels, a controversial design innovation that soon became an Indian trademark. In 1940 the USA had not yet joined in WW 2, and so there was a market for luxury bikes like this Indian.
• a 1918 Cleveland. Lightweight and affordable, the Cleveland was a popular motorcycle with a single cylinder 2.5 hp motor. Adverts claimed that it could achieve 75 mpg and reach up to 40 mph, and that on those 1918 dirt roads!
• a 1970 Chopper. Blame Peter Fonda and Hollywood for this monstrosity ;-)
• a 1965 Hardly-Ableson Electra-Glide, so christened because it introduced the electric starter to those tired of kicking over the big V-twin. Or hardly able, son.

Winston Rand objected to my divulging Rapunzel's little secret on wednesday :-

"Well, in 2 minutes you have destroyed several centuries of romantic myth. 
Next I suppose you will tell me that Snow White's 7 dwarfs were only 
figments of her warped personality dreaming of group sex with little 
people who have very large... noses... ;-)" 

Liz Hinds commented on Blooperman's Fizziks (my October 10th blog-entry), saying "Reading textbooks is a little bit geekish!" and adding "I did like Latin in school though. A sensible language and I didn't have to put on any funny accents!". So I replied to her short eMail with a longer one in Latin (evil grin ;-), to which she replied "You are seriously over-educated!", so we then continued in English, with her asking:

"Now a question for you: why doesn't eth (my mistyping of 'the') come up as
a spelling error? I have answered that for myself, or rather Mr Chambers
has. It's a letter, a barred D used in Old English. Of course."

prompted this reply from me:- "Because there were sounds in Old English (600-1100 AD) that were thought not to be represented by the Roman alphabet, Old English used runic characters for those sounds. The runes were "asc" (pronounced "ash") (æ), "eth" (ð), "thorn" (þ), and "wen" (looks similar to a "p" but with a smaller curved bow). Modern English has 26 letters (German has 30, with ä,ö,ü, and β), Latin 22."
Then we wrapped up the Latin conversation by listening to a Finnish Elvis imitator singing Elvis hits in Latin ;-) I don't think it gets much geekier than that ;-)

Jim Kakalios replied to my criticism of his book (see my October 10th blog-entry Blooperman's Fizziks), confirming his maths error which I found and blogged here. His reply deserves a blog-entry of its own however, which will appear here shortly.

Anna Pashen tells me she likes the science stuff and likes discussing world theories with science geeks at parties, when she's drunk enough to think she understands (her statement, not mine ;-). I offered to blog a deconstruction of string theory, comparing it with e.g. a non-commutative geometry, but both she and Indian UCSB postgrad Ch@ry ( who is Far from Sober) think that it might be a trifle heavy for most of my non-scientific readers. I shall leave out the maths, then I'll test your branes(!)

Haggiswurst is now back again, complaining about life in Mingleton town hall (q.v), so I recommended "What you need in dept S is this special tea mug, with a slot sized exactly for dunking McVitie's digestive biscuits :-)

Three-year blogger Peter C Harris has started a new blog, just for the labels. . .

Carl Rose (writing from Trinidad and Tobago) gives us this heads-up :-

"Don't know if you are aware, but the Royal Society has opened its 
archives [from 1665 on] for viewing and downloading, free till December. 
The web-site is http://www.journals.royalsoc.ac.uk
thought it might be of great interest to you [and the blog readership]".

Local photographer Peter Dück (Lichtenau) sent me his great photograph of my friend Marcus Kroll's tame(?) hunting eagle. Thanks, Peter.

I asked English teacher Malcolm Ford (whom I have not seen for almost 40 years!) to clarify me on when to use "which" vs. "that". I'll pass his tip on to my blogreaders :-

Which should be used for a subordinate clause, 
e.g. " I went to my grandmother's house, which was made of gingerbread" .
Whereas " I went to my grandmother's house that was made of gingerbread" 
implies she has more than one house and this one is made of gingerbread.

Blogreader Ivan, mailing from Kiev, thinks I should explain the latin pun I wrote in the article on Schumi, as not many may have got it. "Sic transit gloria (monday?)" means 'Fame in this world is fleeting (already by monday?)', and was a pun on the Latin quotation "Sic transit gloria mundi". Yes, I confess, my puns are bad. Puns on Monday(!) are especially bad. Bilingual English/Latin puns are worse, but any puns I might make about intergalactic German sausages are surely the Wurst of All ;-)

Jenny (presently in Ibiza) has ordered herself a Rule of History (see my blog entry dated October 22nd) and points us to the $10 Histomap. It is less portable though.

And to finish up on a motorcycle theme again, there was a Thankyou-note from Carlo Rimassa (UK), whom I'd been coaching on riding the old Nurburgring racetrack :-

"Hi there Stu, just a quick note to let you know I went to the Ring 
last weekend, and managed to do the Karussel banked corner, seven times.
I must have gone very slow because I was overtaken on the outside of it
during one lap, but I'm generally happy about it.
To be honest, it's a novelty but it's not a particularly pleasing or
interesting bend. Really just a way to connect the two gradients, but
that's it. Klostertal/SteilStrecken is far more beautiful, actually one of
the best in the whole circuit.

You advice was spot on, and very very useful. 
I thank you again for taking the time to explain to me what to do."

Well done, Carlo, glad I could help. But I'm only a 9-minute++ man these days; however YouTube has an eight-minute on-bike video of a Ring lap by Markus Barth :-)

Copyright ^© Stu Savory on 27th October 2006 at 06:27 CEST permalink Email

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