In (mathematical) billiards, the ball travels in a straight line between impacts with the boundary, when it changes suddenly and discontinuously We can approximate the hard-edged, flat-bedded billiard by a smooth sloping surface, that we call a “ballyard”. Then the continuous dynamics of the ballyard approach the motions on a billiard.

## Archive Page 2

### Learning Maths without even Trying

Published July 18, 2019 Irish Times Leave a CommentTags: Education, Ireland, Recreational Maths

Children have an almost limitless capacity to absorb knowledge if it is presented in an appealing and entertaining manner. Mathematics can be daunting, but it is possible to convey key ideas visually so that they are instantly accessible. Visiting Explorium recently, I saw such a visual display demonstrating the theorem of Pythagoras, which, according to Jacob Bronowski, “remains the most important single theorem in the whole of mathematics” [TM167 or search for “thatsmaths” at irishtimes.com].

We will describe some generic behaviour patterns of dynamical systems. In many systems, the orbits exhibit characteristic patterns called boxes and loops. We first describe orbits for a simple pendulum, and then look at some systems in higher dimensions.

### What did the Romans ever do for Maths?

Published July 4, 2019 Irish Times Leave a CommentTags: Arithmetic, History

The ancient Romans developed many new techniques for engineering and architecture. The citizens of Rome enjoyed fountains, public baths, central heating, underground sewage systems and public toilets. All right, but apart from sanitation, medicine, education, irrigation, roads and aqueducts, what did the Romans ever do for maths? [TM166 or search for “thatsmaths” at irishtimes.com].

### Cumbersome Calculations in Ancient Rome

Published June 27, 2019 Occasional 1 CommentTags: Algorithms, History

“Typus Arithmeticae” is a woodcut from the book *Margarita Philosophica* by Gregor Reisch of Freiburg, published in 1503. In the centre of the figure stands Arithmetica, the muse of mathematics. She is watching a competition between the Roman mathematician Boethius and the great Pythagoras. Boethius is crunching out a calculation using Hindu-Arabic numerals, while Pythagoras uses a counting board or abacus (*tabula*) and – presumably – a less convenient number system. Arithmetica is looking with favour towards Boethius. He smiles smugly while Pythagoras is looking decidedly glum.

The figure aims to show the superiority of the Hindu-Arabic number system over the older Greek and Roman number systems. Of course, it is completely anachronistic: Pythagoras flourished around 500 BC and Boethius around AD 500, while the Hindu-Arabic numbers did not arrive in Europe until after AD 1200.

### Simple Curves that Perplex Mathematicians and Inspire Artists

Published June 20, 2019 Irish Times Leave a CommentTags: Algorithms, Topology

The preoccupations of mathematicians can seem curious and strange to *normal* people. They sometimes expend great energy proving results that appear glaringly obvious. One such result is called the **Jordan** **Curve** **Theorem**. We all know that a circle has an inside and an outside, and that this property also holds for a much larger collection of closed curves [TM165 or search for “thatsmaths” at irishtimes.com].

Continue reading ‘Simple Curves that Perplex Mathematicians and Inspire Artists’

### Bernard Bolzano, a Voice Crying in the Wilderness

Published June 13, 2019 Occasional Leave a CommentTags: Analysis, History

Bernard Bolzano, born in Prague in 1781, was a Bohemian mathematician with Italian origins. Bolzano made several profound advances in mathematics that were not well publicized. As a result, his mathematical work was overlooked, often for many decades after his death. For example, his construction of a function that is continuous on an interval but nowhere differentiable, did not become known. Thus, the credit still goes to Karl Weierstrass, who found such a function about 30 years later. Boyer and Merzbach described Bolzano as “a voice crying in the wilderness,” since so many of his results had to be rediscovered by other workers.

Continue reading ‘Bernard Bolzano, a Voice Crying in the Wilderness’

### Spin-off Effects of the Turning Earth

Published June 6, 2019 Irish Times Leave a CommentTags: Fluid Dynamics, Geophysics, Numerical Weather Prediction

On the rotating Earth, a moving object deviates from a straight line, being deflected to the right in the northern hemisphere and to the left in the southern hemisphere. The deflecting force is named after a nineteenth century French engineer, Gaspard-Gustave de Coriolis [TM164 or search for “thatsmaths” at irishtimes.com].

Coriolis was interested in the dynamics of machines, such as water mills, with rotating elements. He was not concerned with the turning Earth or the oceans and atmosphere surrounding it. But it is these fluid envelopes of the planet that are most profoundly affected by the Coriolis force.

For many decades, a search has been under way to find a *theory of everything*, that accounts for all the fundamental physical forces, including gravity. The dictum “physics is geometry” is a guiding principle of modern theoretical physics. Einstein’s General Theory of Relativity, which emerged just one hundred years ago, is a crowning example of this synergy. He showed how matter distorts the geometry of space and this geometry determines the motion of matter. The central idea is encapsulated in an epigram of John A Wheeler:

From cheetahs chasing gazelles, through coastguards saving shipwrecked sailors, to missiles launched at enemy aircraft, strategies of pursuit and evasion play a role in many areas of life (and death). From pre-historic times we have been solving such pursuit problems. The survival of our early ancestors depended on their ability to acquire food. This involved chasing and killing animals, and success depended on an understanding of relative speeds and optimal pursuit paths.

### The Rise and Rise of Women in Mathematics

Published May 16, 2019 Irish Times Leave a CommentTags: History, Social attitudes

The influential collection of biographical essays by Eric Temple Bell, *Men of Mathematics,* was published in 1937. It covered the lives of about forty mathematicians, from ancient times to the beginning of the twentieth century. The book inspired many boys to become mathematicians. However, it seems unlikely that it inspired many girls: the only woman to get more than a passing mention was Sofia Kovalevskaya, a brilliant Russian mathematician and the first woman to obtain a doctorate in mathematics [TM163 or search for “thatsmaths” at irishtimes.com].

Continue reading ‘The Rise and Rise of Women in Mathematics’

### Bouncing Billiard Balls Produce Pi

Published May 9, 2019 Occasional Leave a CommentTags: Algorithms, Numerical Analysis, Pi

There are many ways of evaluating , the ratio of the circumference of a circle to its diameter. We review several historical methods and describe a recently-discovered and completely original and ingenious method.

### Kepler’s Vanishing Circles Hidden in Hamilton’s Hodograph

Published May 2, 2019 Irish Times Leave a CommentTags: Astronomy, Hamilton, Mechanics

The Greeks regarded the heavens as the epitome of perfection. All flaws and blemishes were confined to the terrestrial domain. Since the circle is perfect in its infinite symmetry, it was concluded by Aristotle that the Sun and planets move in circles around the Earth. Later, the astronomer Ptolemy accounted for deviations by means of additional circles, or epicycles. He stuck with the circular model [TM162 or search for “thatsmaths” at irishtimes.com].

Continue reading ‘Kepler’s Vanishing Circles Hidden in Hamilton’s Hodograph’

### K3 implies the Inverse Square Law.

Published April 25, 2019 Occasional Leave a CommentTags: Astronomy, Mechanics

Kepler formulated three remarkable laws of planetary motion. He deduced them directly from observations of the planets, most particularly of the motion of Mars. The first two laws appeared in 1609 in Kepler’s *Astronomia Nova*. The first law (**K1**) describes the orbit of a planet as an ellipse with the Sun at one focus. The second law (**K2**) states that the radial line from Sun to planet sweeps out equal areas in equal times; we now describe this in terms of conservation of angular momentum.

The third law (**K3**), which appeared in 1619 in Kepler’s *Harmonices Mundi*, is of a different character. It does not relate to a single planet, but connects the motions of different planets. It states that the squares of the orbital periods vary in proportion to the cubes of the semi-major axes. For circular orbits, the period squared is proportional to the radius cubed.

### Closing the Gap between Prime Numbers

Published April 18, 2019 Irish Times Leave a CommentTags: Arithmetic, Number Theory

Occasionally, a major mathematical discovery comes from an individual working in isolation, and this gives rise to great surprise. Such an advance was announced by Yitang Zhang six years ago. [TM161 or search for “thatsmaths” at irishtimes.com].

### Massive Collaboration in Maths: the Polymath Project

Published April 11, 2019 Occasional Leave a CommentTags: Number Theory

Sometimes proofs of long-outstanding problems emerge without prior warning. In the 1990s, Andrew Wiles proved Fermat’s Last Theorem. More recently, Yitang Zhang announced a key result on bounded gaps in the prime numbers. Both Wiles and Zhang had worked for years in isolation, keeping abreast of developments but carrying out intensive research programs unaided by others. This ensured that they did not have to share the glory of discovery, but it may not be an optimal way of making progress in mathematics.

**Polymath**

**Is massively collaborative mathematics possible?** This was the question posed in a 2009 blog post by Timothy Gowers, a Cambridge mathematician and Fields Medal winner. Gowers suggested completely new ways in which mathematicians might work together to accelerate progress in solving some really difficult problems in maths. He envisaged a forum for the online discussion of problems. Anybody interested could contribute to the discussion. Contributions would be short, and could include false routes and failures; these are normally hidden from view so that different workers repeat the same mistakes.

Continue reading ‘Massive Collaboration in Maths: the Polymath Project’

### A Pioneer of Climate Modelling and Prediction

Published April 4, 2019 Irish Times Leave a CommentTags: Climate Modelling, Numerical Weather Prediction

Today we benefit greatly from accurate weather forecasts. These are the outcome of a long struggle to advance the science of meteorology. One of the major contributors to that advancement was Norman A. Phillips, who died in mid-March, aged 95. Phillips was the first person to show, using a simple computer model, that mathematical simulation of the Earth’s climate was practicable [TM160 or search for “thatsmaths” at irishtimes.com].

Continue reading ‘A Pioneer of Climate Modelling and Prediction’

Sitting at the breakfast table, I noticed that a small cereal bowl placed within another larger one was rocking, and that the period became shorter as the amplitude died down. What was going on?

### Joseph Fourier and the Greenhouse Effect

Published March 21, 2019 Irish Times Leave a CommentTags: Applied Maths, Fourier analysis, Geophysics

Jean-Baptiste Joseph Fourier, French mathematician and physicist, was born in Auxerre 251 years ago today. He is best known for the mathematical techniques that he developed in his analytical theory of heat transfer. Over the past two centuries, his methods have evolved into a major subject, harmonic analysis, with widespread applications in number theory, signal processing, quantum mechanics, weather prediction and a broad range of other fields [TM159 or search for “thatsmaths” at irishtimes.com].

### The Kill-zone: How to Dodge a Sniper’s Bullet

Published March 14, 2019 Occasional Leave a CommentTags: Applied Maths, Mechanics

Under mild simplifying assumptions, a projectile follows a parabolic trajectory. This results from Newton’s law of motion. Thus, for a fixed energy, there is an accessible region around the firing point comprising all the points that can be reached. We will derive a mathematical description for this *kill-zone *(the term kill-zone, used for dramatic effect, is the region embracing all the points that can be reached by a sniper’s bullet, given a fixed muzzle velocity).

Family of trajectories with fixed initial speed and varying launch angles. Two particular trajectories are shown in black. Continue reading ‘The Kill-zone: How to Dodge a Sniper’s Bullet’

### Hokusai’s Great Wave and Roguish Behaviour

Published March 7, 2019 Irish Times Leave a CommentTags: Wave Motion

“The Great Wave off Kanagawa”, one of the most iconic works of Japanese art, shows a huge breaking wave with foam thrusting forward at its crest, towering over three fishing boats, with Mt Fuji in the background [TM158 or search for “thatsmaths” at irishtimes.com].

Continue reading ‘Hokusai’s Great Wave and Roguish Behaviour’

### Don’t be Phased by Waveform Distortions

Published February 28, 2019 Uncategorized Leave a CommentTags: Fourier analysis, Music, Wave Motion

For many years there has been an ongoing debate about the importance of phase changes in music. Some people claim that we cannot hear the effects of phase errors, others claim that we can. Who is right? The figure below shows a waveform of a perfect fifth, with components in the ratio for various values of the phase-shift. Despite the different appearances, all sound pretty much the same.

Continue reading ‘Don’t be Phased by Waveform Distortions’### Multiple Discoveries of the Thue-Morse Sequence

Published February 21, 2019 Irish Times Leave a CommentTags: Algorithms, Number Theory

It is common practice in science to name important advances after the first discoverer or inventor. However, this process often goes awry. A humorous principle called Stigler’s Law holds that no scientific result is named after its original discoverer. This law was formulated by Professor Stephen Stigler of the University of Chicago in his publication “Stigler’s law of eponymy”. He pointed out that his “law” had been proposed by others before him so it was, in a sense, self-verifying. [TM157 or search for “thatsmaths” at irishtimes.com].

Continue reading ‘Multiple Discoveries of the Thue-Morse Sequence’### Folding Maps: A Simple but Unsolved Problem

Published February 14, 2019 Occasional Leave a CommentTags: Combinatorics

Paper-folding is a recurring theme in mathematics. The art of origami is much-loved by many who also enjoy recreational maths. One particular folding problem is remarkably easy to state, but the solution remains elusive:

**Given a map with M ****×**** N panels, how many different ways can it be folded? **

Each panel is considered to be distinct, so two foldings are equivalent only when they have the same vertical sequence of the L = M *×* N layers.

### Rambling and Reckoning

Published February 7, 2019 Irish Times Leave a CommentTags: Arithmetic, Recreational Maths

A walk on the beach, in the hills or along a river bank provides great opportunities for mathematical reflection. How high is the mountain? How many grains of sand are on the beach? How much water is flowing in the river? [TM156 or search for “thatsmaths” at irishtimes.com].

While the exact answers may be elusive, we can make reasonable guesstimates using basic knowledge and simple mathematical reasoning. And we will be walking in the footsteps of some of the world’s greatest thinkers.

Continue reading ‘Rambling and Reckoning’### Our Dearest Problems

Published January 31, 2019 Occasional 2 CommentsTags: Puzzles, Recreational Maths

A Colloquium on Recreational Mathematics took place in Lisbon this week. The meeting, RMC-VI (G4GEurope), a great success, was organised by the Ludus Association, with support from several other agencies: MUHNAC, ULisboa, CMAF-IO, CIUHCT, CEMAPRE, and FCT. It was the third meeting integrated in the Gathering for Gardner movement, which celebrates the great populariser of maths, Martin Gardner. For more information about the meeting, see http://ludicum.org/ev/rm/19 .

Continue reading ‘Our Dearest Problems’### Discoveries by Amateurs and Distractions by Cranks

Published January 17, 2019 Irish Times Leave a CommentTags: History, Ramanujan, Recreational Maths

Do amateurs ever solve outstanding mathematical problems? Professional mathematicians are aware that almost every new idea they have about a mathematical problem has already occurred to others. Any really new idea must have some feature that explains why no one has thought of it before [TM155 or search for “thatsmaths” at irishtimes.com].

Continue reading ‘Discoveries by Amateurs and Distractions by Cranks’

### Really, 0.999999… is equal to 1. Surreally, this is not so!

Published January 10, 2019 Occasional Leave a CommentTags: Analysis, Number Theory

The value of the recurring decimal 0.999999 … is a popular topic of conversation amongst amateur mathematicians of various levels of knowledge and expertise. Some of the discussions on the web are of little value or interest, but the topic touches on several subtle and deep aspects of number theory.

Continue reading ‘Really, 0.999999… is equal to 1. Surreally, this is not so!’

### Trappist-1 & the Age of Aquarius

Published January 3, 2019 Irish Times Leave a CommentTags: Astronomy, Mechanics

The Pythagoreans believed that the planets generate sounds as they move through the cosmos. The idea of the harmony of the spheres was brought to a high level by Johannes Kepler in his book *Harmonices Mundi*, where he identified many simple relationships between the orbital periods of the planets [TM154 or search for “thatsmaths” at irishtimes.com].

Kepler’s idea was not much supported by his contemporaries, but in recent times astronomers have come to realize that resonances amongst the orbits has a crucial dynamical function. Continue reading ‘Trappist-1 & the Age of Aquarius’

###
Gaussian Curvature: the *Theorema Egregium*

Published December 27, 2018
Occasional
9 Comments
Tags: Gauss, Geometry

*Theorema Egregium*or outstanding theorem. In 1828 he published his “Disquisitiones generales circa superficies curvas”, or

*General investigation of curved surfaces*. Gauss defined a quantity that measures the curvature of a two-dimensional surface. He was inspired by his work on geodesy, surveying and map-making, which involved taking measurements on the surface of the Earth. The total curvature — or Gaussian curvature — depends only on measurements within the surface and Gauss showed that its value is independent of the coordinate system used. This is his

*Theorema Egregium*. The Gaussian curvature characterizes the intrinsic geometry of a surface.

Continue reading ‘Gaussian Curvature: the *Theorema Egregium*‘

### Consider a Spherical Christmas Tree

Published December 20, 2018 Irish Times Leave a CommentTags: Algorithms, Topology

A minor seasonal challenge is how to distribute the fairy lights evenly around the tree, with no large gaps or local clusters. Since the lights are strung on a wire, we are not free to place them individually but must weave them around the branches, attempting to achieve a pleasing arrangement. Optimization problems like this occur throughout applied mathematics [TM153 or search for “thatsmaths” at irishtimes.com].

Trees are approximately conical in shape and we may assume that the lights are confined to the surface of a cone. The peak, where the Christmas star is placed, is a mathematical singularity: all the straight lines that can be drawn on the cone, the so-called generators, pass through this point. Cones are *developable* surfaces: they can be flattened out into a plane without being stretched or shrunk.

### The 3 : 2 Resonance between Neptune and Pluto

Published December 13, 2018 Occasional 1 CommentTags: Astronomy

For every two orbits of Pluto around the Sun, Neptune completes three orbits. This 3 : 2 resonance has profound consequences for the stability of the orbit of Pluto.

Continue reading ‘The 3 : 2 Resonance between Neptune and Pluto’

### Random Numbers Plucked from the Atmosphere

Published December 6, 2018 Irish Times Leave a CommentTags: Number Theory

Randomness is a slippery concept, defying precise definition. A simple example of a random series is provided by repeatedly tossing a coin. Assigning “1” for heads and “0” for tails, we generate a random sequence of binary digits or *bits*. Ten tosses might produce a sequence such as 1001110100. Continuing thus, we can generate a sequence of any length having no discernible pattern [TM152 or search for “thatsmaths” at irishtimes.com].

Continue reading ‘Random Numbers Plucked from the Atmosphere’

### The Two Envelopes Fallacy

Published November 29, 2018 Occasional 1 CommentTags: Probability, Puzzles

During his Hamilton lecture in Dublin recently, Fields medalist Martin Hairer made a passing mention of the “Two Envelopes Paradox”. This is a well-known problem in probability theory that has led to much misunderstanding. It was originally developed in 1912 by the leading German number theorist Edmund Landau (see Gorroochurn, 2012). It is frequently discussed on the web, with much misunderstanding and confusion. I will try to avoid adding to that.

### Gravitational Waves & Ringing Teacups

Published November 22, 2018 Occasional Leave a CommentTags: Astronomy, Relativity, Wave Motion

Newton’s law of gravitation describes how two celestial bodies orbit one another, each tracing out an elliptical path. But this is imprecise: the theory of general relativity shows that two such bodies radiate energy away in the form of * gravitational waves* (GWs), and spiral inwards until they eventually collide.

### The “Napoleon of Crime” and The Laws of Thought

Published November 15, 2018 Irish Times Leave a CommentTags: History, Logic

A fascinating parallel between a brilliant mathematician and an arch-villain of crime fiction is drawn in a forthcoming book – *New Light on George Boole –* by Des MacHale and Yvonne Cohen. Professor James Moriarty, master criminal and nemesis of Sherlock Holmes, was described by the detective as “the Napoleon of crime”. The book presents convincing evidence that Moriarty was inspired by Professor George Boole [TM151, or search for “thatsmaths” at irishtimes.com].

Continue reading ‘The “Napoleon of Crime” and The Laws of Thought’

### Listing the Rational Numbers III: The Calkin-Wilf Tree

Published November 8, 2018 Occasional Leave a CommentTags: Arithmetic, Number Theory

The rational numbers are countable: they can be put into one-to-one correspondence with the natural numbers. In previous articles we showed how the rationals can be presented as a list that includes each rational precisely once. One approach leads to the Farey Sequences. A second, related, approach gives us the Stern-Brocot Tree. Here, we introduce another tree structure, The Calkin-Wilf Tree.

Continue reading ‘Listing the Rational Numbers III: The Calkin-Wilf Tree’

### Johannes Kepler and the Song of the Earth

Published November 1, 2018 Irish Times 2 CommentsTags: Astronomy, Music

Johannes Kepler, German mathematician and astronomer, sought to explain the solar system in terms of divine harmony. His goal was to find a system of the world that was mathematically correct and harmonically pleasing. His methodology was scientific in that his hypotheses were inspired by and confirmed by observations. However, his theological training and astrological interests influenced his thinking [TM150, or search for “thatsmaths” at irishtimes.com].

Continue reading ‘Johannes Kepler and the Song of the Earth’

### Saving Daylight with Hip-hop Time: a Modest Proposal

Published October 25, 2018 Occasional Leave a CommentTags: Time measurement

At 2:00 AM on Sunday 28 October the clocks throughout Europe will be set back one hour, reverting to Standard Time. In many countries, the clocks are put forward one hour in Spring and set back to Standard Time in the Autumn. Daylight saving time gives brighter evenings in Summer.

In Summer, the mornings are already bright before most of us wake up but, in Winter, the mornings would be too dark unless we reverted to Standard Time.

Continue reading ‘Saving Daylight with Hip-hop Time: a Modest Proposal’

### Who Uses Maths? Almost Everyone!

Published October 18, 2018 Irish Times Leave a CommentTags: Education

In the midst of Maths Week Ireland, many students may be asking “What use is mathematics and what purpose is served by studying it?” Mathematicians often stress the inherent beauty and intellectual charm of the subject, but that is unlikely to persuade many people, who demand to know how mathematics can be of use and value to them. [TM149, or search for “thatsmaths” at irishtimes.com].

In reality, mathematics is essential in numerous contexts: the diversity is remarkable, and you may be surprised how maths plays a vital role in the everyday work of so many people.

### Listing the Rational Numbers II: The Stern-Brocot Tree

Published October 11, 2018 Occasional Leave a CommentTags: Arithmetic, Number Theory

The rational numbers are countable: they can be put into one-to-one correspondence with the natural numbers. But it is not obvious how to construct a list that is sure to contain every rational number precisely once. In a previous post we described the Farey Sequences. Here we examine another, related, approach.

Continue reading ‘Listing the Rational Numbers II: The Stern-Brocot Tree’

### The Many Modern Uses of Quaternions

Published October 4, 2018 Irish Times 1 CommentTags: Algebra, Hamilton

The story of William Rowan Hamilton’s discovery of new four-dimensional numbers called quaternions is familiar. The solution of a problem that had bothered him for years occurred to him in a flash of insight as he walked along the Royal Canal in Dublin. But this Eureka moment did not arise spontaneously: it was the result of years of intense effort. The great French mathematician Henri Poincaré also described how sudden inspiration occurs unexpectedly, but always following a period of concentrated research [TM148, or search for “thatsmaths” at irishtimes.com].

### Listing the Rational Numbers: I. Farey Sequences

Published September 27, 2018 Occasional Leave a CommentTags: Arithmetic, Number Theory

We know, thanks to Georg Cantor, that the rational numbers — ratios of integers — are countable: they can be put into one-to-one correspondence with the natural numbers.

Continue reading ‘Listing the Rational Numbers: I. Farey Sequences’

### Tom Lehrer: Comical Musical Mathematical Genius

Published September 20, 2018 Irish Times Leave a CommentTags: Education, Music, Recreational Maths

Tom Lehrer, mathematician, singer, songwriter and satirist, was born in New York ninety years ago. He was active in public performance for about 25 years from 1945 to 1970. He is most renowned for his hilarious satirical songs, many of which he recorded and which are available today on YouTube [see TM147, or search for “thatsmaths” at irishtimes.com].

Continue reading ‘Tom Lehrer: Comical Musical Mathematical Genius’

### A Trapezoidal Prism on the Serpentine

Published September 13, 2018 Occasional Leave a CommentTags: Geometry

Walking in Hyde Park recently, I spied what appeared to be a huge red pyramid in the middle of the Serpentine. On closer approach, and with a changing angle of view, it became clear that it was prismatic in shape, composed of numerous barrels in red, blue and purple.

### Face Recognition

Published September 6, 2018 Irish Times Leave a CommentTags: Algorithms, Computer Science, Social attitudes

As you pass through an airport, you are photographed several times by security systems. Face recognition systems can identify you by comparing your digital image to faces stored in a database. This form of identification is gaining popularity, allowing you to access online banking without a PIN or password. [see TM146, or search for “thatsmaths” at irishtimes.com].

### A Zero-Order Front

Published August 30, 2018 Occasional Leave a CommentTags: Fluid Dynamics, Geophysics, modelling

Sharp gradients known as fronts form in the atmosphere when variations in the wind field bring warm and cold air into close proximity. Much of our interesting weather is associated with the fronts that form in extratropical depressions.

Below, we describe a simple mechanistic model of frontogenesis, the process by which fronts are formed.

### The Flight of the Bumble Bee

Published August 23, 2018 Occasional Leave a CommentTags: Algebra, Puzzles

Alice and Bob, initially a distance *l* apart, walk towards each other, each at a speed *w*. A bumble bee flies from the nose of one to the nose of the other and back again, repeating this zig-zag flight at speed *f *until Alice and Bob meet. *How far does the bumble bee fly?*

### The Miraculous Spiral on Booterstown Strand

Published August 16, 2018 Irish Times Leave a CommentTags: biology, Geometry, Geophysics

We all know what a spiral looks like. Or do we? Ask your friends to describe one and they will probably trace out the form of a winding staircase. But that is actually a helix, a curve in three-dimensional space. A spiral is confined to a plane – it is a flat curve. In general terms, a spiral is formed by a point moving around a fixed centre while its distance increases or decreases as it revolves [see TM145, or search for “thatsmaths” at irishtimes.com].

Continue reading ‘The Miraculous Spiral on Booterstown Strand’