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Tides: a Tug-of-War between Earth, Moon and Sun

Published August 2, 2018 Irish Times Leave a Comment
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All who set a sail, cast a hook or take a dip have a keen interest in the water level, and the regular ebb and flow of the tides. At most places the tidal variations are semi-diurnal, with high and low water twice each day  [see TM144, or search for “thatsmaths” at irishtimes.com].

TidePrediction-NewYork-KurilIslands

Animation of tide prediction machine, showing outputs for New York (semi-diurnal tides) and Kuril Islands (diurnal tides) [Source: American Mathematical Society (see below)].

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Grandi’s Series: A Second Look

Published July 26, 2018 Occasional Leave a Comment
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Grandis-Series
In an earlier post, we discussed Grandi’s series, originally studied by the Italian monk Dom Guido Grandi around 1703. It is the series

\displaystyle G = 1 - 1 + 1 - 1 + 1 - 1 + \dots

This is a divergent series: the sequence of partial sums is {\{ 1, 0, 1, 0, 1, 0, \dots \}}, which obviously does not converge, but alternates between {0} and {1}.

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The Empty Set is Nothing to Worry About

Published July 19, 2018 Irish Times Leave a Comment
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Today’s article is about nothing: nothing at all, as encapsulated in the number zero and the empty set. It took humanity millennia to move beyond the counting numbers. Zero emerged in several civilizations, first as a place-holder to denote a space or gap between digits, and later as a true number, which could be manipulated like any other. [see TM143, or search for “thatsmaths” at irishtimes.com].

Zero-Images

A selection of images of zero (google images).

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Grandi’s Series: Divergent but Summable

Published July 12, 2018 Occasional Leave a Comment
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Is the Light On or Off?

Suppose a light is switched on for a half-minute, off for a quarter minute, on for one eighth of a minute and so on until precisely one minute has elapsed. Is the light on or off at the end of this (infinite) process? Representing the two states “on” and “off” by {1} and {0}, the sequence of states over the first minute is {\{ 1, 0, 1, 0, 1, 0, \dots \}}. But how do we ascertain the final state from this sequence? This question is sometimes known as Thomson’s Lamp Puzzle.

Grandis-Series

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Trigonometric Comfort Blankets on Hilltops

Published July 5, 2018 Irish Times Leave a Comment
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On a glorious sunny June day we reached the summit of Céidín, south of the Glen of Imall, to find a triangulation station or trig pillar. These concrete pillars are found on many prominent peaks throughout Ireland, and were erected to aid in surveying the country  [see TM142, or search for “thatsmaths” at irishtimes.com].

TrigPillar-CroaghanMoire

Trig pillar on summit of Croaghan Moira, Wicklow [Image from https://mountainviews.ie/%5D.

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Numbers with Nines

Published June 28, 2018 Occasional Leave a Comment
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What proportion of all numbers less than a given size N have a 9 in their decimal expansion? A naive argument would be that, since 9 is one of ten distinct digits, the answer must be about 10%. But this is not “remotely close” to the true answer.

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Optical Refinements at the Parthenon

Published June 21, 2018 Irish Times Leave a Comment
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The Parthenon is a masterpiece of symmetry and proportion. This temple to the Goddess Athena was built with pure white marble quarried at Pentelikon, about 20km from Athens. It was erected without mortar or cement, the stones being carved to great accuracy and locked together by iron clamps. The building and sculptures were completed in just 15 years, between 447 and 432 BC. [TM141 or search for “thatsmaths” at irishtimes.com].

Parthenon-Photo

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