Calendar for May

The next calendar (click for hi-res image). Lots of anniversaries coming up, including 100 years since the eclipse test of general relativity and 40 years since the movie Alien. Also, the new SI units come into force.

See more calendars here.


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Revising the Metric System


Relationship between the new SI units (image produced using the igraph package of R)

On May 20, a major redefinition of SI (metric) units comes into force. In particular, the second, metre, ampere, mole, kilogram, kelvin, and candela will be defined as follows:

The second (unit of time)

As it is now, the second will be defined using ultra-precise caesium clocks. Specific microwave radiation from caesium atoms is defined to have a frequency of exactly 9.192 631 770 GHz. That is, counting 9,192,631,770 waves will take exactly one second.

The metre (unit of length)

As it is now, the metre will be defined using the speed of light, which is defined to be exactly 299,792,458 metres per second. That is, the metre is the distance travelled by light in one 299,792,458th of a second (where the second is defined as above).

The ampere (unit of electric current)

The definition of the ampere (amp) has been greatly simplified, taking account of the connection between electricity and electrons. The ampere is a coulomb of electric charge flowing past a given point per second, and the charge on a single electron is now defined to be 1.602 176 634 × 10−19 coulombs. Thus an ampere is about 6,241,509,074 billion electrons flowing past a given point in a second.

As a consequence of this new definition, two important natural constants which used to have defined values (the permeability of free space and the permittivity of free space) now have experimentally determined ones. This will require rewriting pretty much every physics and electrical engineering textbook.

The mole (unit of amount of substance)

The mole represents Avogadro’s number of atoms, molecules, or other particles. Previously, Avogadro’s number was defined to be the number of carbon atoms in 12 grams of pure carbon-12. It is now defined to be exactly 6.022 140 76 × 1023.

The kilogram (unit of mass)

Until 2019, the kilogram was defined by the mass of a specific metal cylinder held in Paris. This has been felt to be unsatisfactory for many years. The current definition uses the fact that the energy of a light photon (in joules) is its frequency times Planck’s constant h, which is defined to be exactly 6.626 070 15 × 10−34.

In practice, a Kibble balance will be used to measure weights by balancing them against an electrically produced force. Units derived from the kilogram include:

  • The newton (unit of force): the force needed to accelerate 1 kilogram at a rate of 1 metre per second squared
  • The pascal (unit of pressure): 1 newton of force per square metre
  • The joule (unit of energy): the energy used in applying a force of 1 newton over a distance of 1 metre
  • The watt (unit of power): 1 joule of energy per second
  • The volt (unit of electric potential): the amount of electric potential across a resistance producing 1 watt of heat per ampere of current
  • The ohm (unit of electrical resistance): the resistance which produces 1 ampere of current when 1 volt of electric potential is applied

See also what NIST has to say about the kilogram.

The kelvin (unit of temperature)

Temperature in degrees Celsius was originally measured on a scale with 0 °C being the freezing point of water and 100 °C the boiling point (at standard pressure). The lowest possible temperature turned out to be absolute zero, −273.15 °C. In 1954, the two fixed points on the scale were changed to −273.15 °C (0 kelvins) and the triple point of water, 0.01 °C (273.16 kelvins).

This definition proved unhelpful for calibrating thermometers intended for very high temperatures, and the current definition uses the fact that the average translational kinetic energy (in joules) of a moving atom of a monoatomic ideal gas is (3/2k T, where T is the temperature of the gas in kelvins, and the Boltzmann constant k is defined to be exactly 1.380 649 × 10−23.

The candela (unit of luminous intensity in a given direction)

The definition of the candela remains what it has been, except that it is influenced by the change in definition of the kilogram (and hence the watt). A light source that emits monochromatic yellowish-green light at a frequency of 540 THz (roughly 555 nm wavelength) is taken to emit 683 lumens per watt, and a light source that uniformly radiates 1 candela in all directions has a total luminous flux of 4π lumens (the constant 683 reflects the human ability to perceive light). The lux is a lumen per square metre.

The dream

When the metric system was first introduced, the metre was defined in terms of the world (1/10,000,000 of the distance between the Equator and the North Pole, measured via Paris). Today, the metric system carries that philosophy to its ultimate conclusion, with all units except the candela defined in terms of the universe. Five of the units are defined in terms of fundamental physical constants: the speed of light (first measured by Rømer in 1676), the charge on the electron (first measured directly by Robert A. Millikan in 1909), the Avogadro constant (measured several ways by Jean Perrin around 1910), and the Planck and Boltzmann constants (first defined by Max Planck around 1900).

The redefined metric system is a little difficult to grasp without understanding modern physics, but fortunately most of us will just keep on using exactly the same measurement instruments as we have done for years.


2019 World Solar Challenge update #4


The happy champions from Delft on stage at the BWSC 2017 awards night (photo: Anthony Dekker)

Here is a further update on the 51 teams (27 Challengers, 23 Cruisers, and 1 Adventure car) aiming for the 2019 Bridgestone World Solar Challenge in Australia this coming October. Many teams are busy with construction, and below is my best understanding of the current team status (it does not yet reflect the to-be-published official list of teams).

Meanwhile, 26 teams – Bridger, Calgary, CalSol (1st in 2017), Esteban (3rd in 2017), Florida, Ga Tech, Illini, Illinois St, Kentucky, Mich St, Missouri S&T, NCSU, NJIT, Northwestern, Principia, PrISUm, Purdue, Rutgers, SIUE, UBC, UPRM, USC, UT, UVA, W Mich, and Waterloo, including 1 WSC team – are preparing to attend FSGP 2019 in America this July.

Recent BWSC news is that Twente has revealed their design and that Stanford has shown the world their shell.

AU  Looks on track  Adelaide University 

Challenger (Lumen II) – they have been doing a lot of testing.

AU  Hmmm  ATN Solar Car Team 

Cruiser (new team: see my team bio) – their team is a mixture of lecturers and students from five universities across Australia. They have tested a model in a wind tunnel.

AU  Hmmm  Australian National University 

Challenger (new car: MTAA Gnowee) – the car is named after a woman in Aboriginal myth who carries the sun.


public domain photo

AU  Looks on track  Flinders University 

Cruiser (Investigator Mark III) – they are planning to improve aerodynamics, reduce weight, and make some other changes.

AU  Looks on track  TAFE SA 

Cruiser (SAV) – this time they will tow the trailer that belongs with the car.

AU  Looks on track  Team Arrow 

Cruiser (ArrowSTF) – as well as racing, their commercial arm, Prohelion, is selling power packages.

AU  Looks on track  University of New South Wales / Sunswift 

Cruiser (Violet) – they have been testing their car on the track.

AU  Looks on track  Western Sydney Solar Team 

Challenger (new car) – they won the American Solar Challenge last year (with their Challenger car Unlimited 2.0).

Western Sydney BWSC 2017 pre-race vlog (they came 6th in the Challenger class)

BE  Looks on track  Agoria Solar Team (KU Leuven) 

Challenger (new car: BluePoint) – they have some (top secret) production moulds and are now sponsored by Agoria.

CA  Looks on track  ETS Quebec (Eclipse) 

Challenger (Éclipse X.I) – they came an excellent 3rd in the ASC, 102 minutes behind Western Sydney, and hope to go even faster with the new battery pack in their modified car. Planned improvements are summarised in their winter newsletter.

CA  Looks on track  University of Toronto (Blue Sky) 

Challenger (new car: Viridian) – they plan to unveil the new car in July.

BWSC 2017 aftermovie (they came 11th in the Challenger class)

CL  Looks on track  Antakari Solar Team 

Challenger (new car: Intikallpa V) – no news on the new design as yet.

Antakari BWSC 2013 aftermovie (they participated in the Adventure class)

CL  Hmmm  Eolian AutoSolar 

Cruiser (new car: Auriga ) – they will be back at the WSC after coming 14th in 2007.


public domain photo

DE  Looks on track  Bochum University of Applied Sciences 

Cruiser (new car) – Bochum also has a solar buggy team.

DE  Looks on track  Sonnenwagen Aachen 

Challenger (new car) – they have a car-racing game app starring their car.

Sonnenwagen Aachen BWSC 2017 aftermovie (they raced in the Challenger class)

HK  Looks on track  Hong Kong Institute of Vocational Education 

Cruiser (Sophie 6 plus) – they have been working on the car body.

IN  Hmmm  R.V. College of Engineering 

Challenger (new car) – no details as yet.


public domain photo

IN  Hmmm  SolarMobil Manipal 

Cruiser (SM-S2) – existing car.

IT  Hmmm  Futuro Solare Onlus 

Cruiser (new car: Archimede 2.0) – they have an exciting design concept.

IT  Looks on track  Onda Solare 

Cruiser (Emilia 4) – they won the American Solar Challenge (Cruiser class) last year, and they have written up their design process here.

JP  Looks on track  Kogakuin University 

Challenger (new car) – they have officially announced their participation.

Kogakuin BWSC 2017 aftermovie (they came 7th in the Challenger class)

JP  Looks on track  Nagoya Institute of Technology 

Challenger (new car) – no news on the new design as yet.


public domain photo

JP  Looks on track  Tokai University 

Challenger (new car) – in January they hosted some visitors from Lodz.

KR  Looks on track  Kookmin University Solar Team 

Challenger (new car) – no news on the new design as yet.

KUST BWSC 2017 aftermovie (they raced in the Challenger class)

MY  Looks on track  EcoPhoton / UiTM 

Challenger (new car: Tigris) – see their first vlog (in Bahasa Malaysia).

MA  Hmmm  Mines Rabat Solar Team 

Challenger (new car: Eleadora 2) – their new catamaran will look like this.

NL  Looks on track  Solar Team Eindhoven 

Cruiser (new car: Stella ?) – they are turning a shipping container into an oven for production and plan to reveal their car on July 4.

Eindhoven BWSC 2017 pre-race news coverage (they came 1st in the Cruiser class)

NL  Looks on track  Solar Team Twente 

Challenger (new car: Red E) – they are already producing regular vlogs, and have a vlog for February (Dutch only). They have revealed their design, which is a GaAs catamaran (see the animation here). They will run a MOOC explaining the design of their 2015 car.

NL  Looks on track  Top Dutch Solar Racing 

Challenger (new team: see my team bio) – they have made good progress on fabrication as well as doing promotion.

NL  Looks on track  Vattenfall Solar Team (Delft) 

Challenger (new car: Nuna X) – these are the champions formerly known as Nuon. See their 2017 aftermovie.

PL  Looks on track  Lodz Solar Team 

Cruiser (Eagle Two) – they have produced a solar baby, which is a prize that lasts.

PL  Hmmm  PUT Solar Dynamics 

Cruiser (new team) – they are ready to begin 3D-printing some prototypes.

RU  Hmmm  Polytech Solar 

Cruiser (new car) – no news on the new design as yet.


public domain photo

SG  Looks on track  Singapore Polytechnic 

Cruiser (SunSPEC 5) – they have new motors and new doors.

SE  Looks on track  Chalmers Solar Team 

Challenger (new team: see my team bio) – their final render resembles the car of the South African NWU team. They have been working on their suspension.

SE  Looks on track  Halmstad University Solar Team 

Challenger (new team: see my team bio) – they are planning a bullet car, much like Michigan’s 2017 entry.

SE  Looks on track  JU Solar Team 

Challenger (new car) – they have a rolling test chassis. The body design seems long and thin.

SE  Looks on track  MDH Solar Team 

Challenger (MDH Solar Car) – they have been doing some testing.

CH  Looks on track  Solar Energy Racers 

Challenger (SER-3) – they raced this car in South Africa.

TW  Looks on track  Kaohsiung / Apollo 

Cruiser (new car: Apollo IX) – they have been making some carbon-fibre seats.

TH  Hmmm  Siam Technical College 

Cruiser (new car: STC-3) – no news on the new design as yet.

Siam Technical College BWSC 2017 aftermovie (they raced in the Cruiser class)

TR  Hmmm  Dokuz Eylül University (Solaris) 

Challenger (new car) – they expect the new car to be 44% more efficient than the 2015 model.


public domain photo

GB  Looks on track  Ardingly College 

Cruiser – this high-school team came 6th in the iESC Cruiser class.

GB  Looks on track  Cambridge University 

Cruiser (new car: Helia) – they are busy with fabrication.

GB  Looks on track  Durham University 

Challenger (new car: Ortus) – they have begun fabrication.

US  Looks on track  Appalachian State University (Sunergy) 

Cruiser (new team: see my team bio) – as with some European teams, they have been testing at an airport.

US  Looks on track  Berkeley (CalSol) 

Cruiser (new car: Tachyon) – they have a bottom shell and roll cage. They will also attend FSGP 2019.

US  Looks on track  Houston School District 

Adventure (Sundancer) – this high school team from from Houston, Mississippi is a regular visitor, because they keep winning the US high school race.

US  Looks on track  Stanford Solar Car Project 

Challenger (new car) – they have revealed their shell, which is a unique asymmetric bullet car.

US  Looks on track  University of Michigan 

Challenger (new car) – they are asking for name suggestions for the new car.

Michigan BWSC 2017 aftermovie (they came 2nd in the Challenger class)

US  Looks on track  University of Minnesota Solar Vehicle Project 

Cruiser (new car: Freya) – no news on the new design as yet.

UMNSVP BWSC 2015 aftermovie (they came 5th in the Cruiser class)

This page last updated 19:37 on 8 April 2019 AEST