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PostPosted: Tue Feb 07, 2012 1:14 pm 
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Thank you very much for a very useful idea. :D

The gate the characters used to travel to Phalanos is a two way
gate, and the characters have to return to Earth for their supplies
anyway, so it is quite likely that they will also bring a crossbow -
for example one which is used for grapnels during the exploration
of a mountainous region.

The observation that the crossbow grapnel is constantly flying fur-
ther or higher than on Earth although the crossbow has the same
power as on Earth would make a nice "material evidence" besides
"feeling lighter" and could well be used to give the characters a
plausible reason to think of other experiments.


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PostPosted: Tue Feb 07, 2012 5:31 pm 
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I'm sorry, I've only just realised that your scenario is that scholars from mediaeval Earth are going to Tau Ceti. I have been thinking in terms of modern people doing so.

Mediaeval scholars have no hope whatsoever of measuring the acceleration due to gravity. The very concept that such a thing exists is not available to them. It was Galileo Galilei who worked out that falling objects accelerate as they fall, and it was he who worked out that there is a constant parameter shared by the falling of heavy things and the falling of light things, and measured it. He did that work about 1600, more than a century after the end of the mediaeval period.

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PostPosted: Tue Feb 07, 2012 5:48 pm 
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Well, the medieval equivalent of the concept of gravity was the idea
that things fall to the ground because this is where they belong. The
observation that something - for example a crossbow bolt - on Phala-
nos does not fall to the ground as fast as it does on Earth could well
lead to another idea which is much closer to our concept of gravity.

This would not be entirely "unhistorical" (which the setting is anyway),
the idea that bodies attract each other has been known to Indian and
Arab scientists since at least the 11th century, just the Europeans we-
re slow learners. In a setting where magic exists and observations on
planets with different gravity can be compared, an earlier discovery of
something like the modern concept of gravity and the intention to in-
vestigate and if possible measure it seems quite possible.


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PostPosted: Tue Feb 07, 2012 6:04 pm 
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rust wrote:
the idea that bodies attract each other has been known to Indian and
Arab scientists since at least the 11th century

I didn't know that. Can you tell me where I can find out more about it?

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PostPosted: Tue Feb 07, 2012 6:10 pm 
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I think the most famous Indian scientist who mentioned the idea (and an
astonishing number of other rather modern ideas) was Bhaskaracharya.
His writings remained the standard textbooks for Indian astronomers and
mathematicians for centuries, and much of this knowledge also travelled
westwards to his Arab colleagues.

http://veda.wikidot.com/bhaskaracharya

As for the Arab scientists, the names to research would be Al-Biruni and
Al-Khazini.

http://glps2.org/wiki/index.php?title=O ... Al-Khazini

Unfortunately I did not find better links in English.


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PostPosted: Tue Feb 07, 2012 11:42 pm 
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Thanks for the links. Bhaskarachārya in particular sounds very interesting. By the sound of things he could have made it to the Theory of Gravity if he had known what Newton learned from the work of Kepler and Galileo: that statement of his quoted on the linked page is the key insight which Newton went on to check by comparing the acceleration of the Moon in its orbit (from Kepler) to that e.g. of an apple falling off a tree (from Galileo).

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PostPosted: Wed Feb 08, 2012 3:33 pm 
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Thinking of it, there could be the potential for a nice adventure,
with the characters sent on a diplomatic mission to the court of
Emperor Frederick II in southern Italy to ask the Arab scholars li-
ving there as guests of the Emperor for the permission to copy
some of their texts on astronomy and physics ... since I have al-
ready decided that the campaign will start around 1220 AD, this
could fit in rather well.


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PostPosted: Thu Apr 05, 2012 12:06 am 
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Um.

Why use candles for accurate time measurement?

Even the ancients had better methods!

Hourglasses (C8th AD at the earliest), once they figure out to use powdered eggshells for the "sand" rather than actual sand (which is an abrasive and gradually widens the hole to make the hourglass less accurate) ... oh, note that "hourglass" is a generic term ... they came in a variety of sizes and durations, down to, IIRC, the minute and half minute.

Clepsydrae also (4000 BC in China! Used as stopwatches to time customers in Athenian Brothels by 400 BC!) would be an earlier possibility.

In fact, Clepsydrae would be the easiest to use ... as long as you could get standard heights ... just use the same clepsydra at more than one location and you could tell if the time taken to fall was different. It would be difficult, I guess, to determine the exact amount of difference, but you could work it out +/- the "standard" for sure.

Phil


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PostPosted: Thu Apr 05, 2012 12:48 am 
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EDG wrote:
Drop a ball, see how fast it falls? That's the time-honoured way of measuring gravity in physics classrooms :)


Or, like the 4th Doctor, use a yo-yo :D


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PostPosted: Thu Apr 05, 2012 7:45 am 
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Scarecrow wrote:
Or, like the 4th Doctor, use a yo-yo :D

:shock: :o :D


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