# 2015 News

### 13 December 2015 – Hexa-tetraflexagon

For Christmas 2015 I have created a hexa-tetraflexagon that tells a simple Christmas story using Bible verses. From a cover page the flexagon can be flexed to two story lines, about either Mary and Joseph, the census, and Jesus being born in a stable, or the shepherds and the wise men visiting.

Download as a hexa-tetraflexagon PDF. It's rectangular, to be printed on an A4 sheet. Merry Christmas.

### 1 November 2015 – New pages

Another maths pages has been added: Key Words in Maths Algebra Exams. Some questions in algebra exams use key words which tell students what is required. The page includes a few examples and links to the pages on this site which further explain the techniques.

A new physics page has been added: Back-of-the-envelope Calculations. A "back-of-the-envelope" calculation is one that is done very roughly, to give an idea of whether something will work. To do the working any scrap of paper will do, including the back of an envelope; no calculators should be required.

### 18 October 2015 – More maths info

Two recent maths pages have been added with information on complex numbers and how to factorise and solve quadratic equations.

### 30 July 2015 – Microwave space drive

The NZ Herald this morning included a story about a microwave propulsion drive that (so the claim goes) is hugely more effective than rocket technology. The article (emphasis added) starts thus:

Interplanetary travel could be a step closer after scientists confirmed that an electromagnetic propulsion drive, which is fast enough to get to the Moon in four hours, actually works.

The whole thrust (ha ha) of the article is that the effect is real and is massively upscalable to the point that a space probe could reach Alpha Centauri in just 100 years, not the tens of thousands of years it would take with a rocket or ion drive. The article even does a bit of name-dropping to back up the effectiveness of the technology.

However in recent years Nasa has confirmed that they believe it works and this week Martin Tajmar, a professor and chairman for space systems at Dresden University of Technology in Germany also showed that it produces thrust.

Believing something works is far short of verifying by repeatable experimental evidence that it works, and whether thrust is produced is irrelevant for space travel if it cannot be upscaled as claimed – something completely untested so far.

If it really worked as claimed this would be revolutionary technology; the NZ Herald would have the story emblazoned across the front page instead of tucked away on page A18. But the trouble is that the idea is actually very controversial and the main claims have not been tested. Indeed, the best tests so far have not been able to show that the thrust is not just a misinterpretation of physical processes. (Even taking the microwave resonator out of the circuit and replacing it with a resistor resulted in a small amount of thrust.) The final paragraph of the article is telling.

"Our test campaign cannot confirm or refute the claims of the EM Drive but intends to independently assess possible side-effects in the measurements methods used so far," said Tajmar. "Nevertheless, we do observe thrust close to the actual predictions after eliminating many possible error sources that should warrant further investigation into the phenomena."

The article says Martin Tajmar has shown that it works, with the implication that it is useful for going to the Moon in four hours, but finishes by quoting him saying his tests cannot confirm the claims. In other words, it seems that a small amount of thrust is produced, but what that thrust is caused by is unknown, and a few micronewtons of thrust do not support the claim it's going to be useful for getting anywhere in space. (Compare with the Apollo lunar module with a gross mass of 4.7 tonnes and equipped with an ascent propulsion system providing thrust of 16 kN. That's 320 million times as much thrust as NASA has measured from a microwave resonator.)

The NZ Herald has done itself a disservice in publishing such a misleading and contradictory article.

The question must also be asked: What are the "actual predictions" the observed thrust is close to when (as the article itself acknowledges) present physics theories say there should be no thrust?

We haven't seen the last of this story, but it seems very likely that no significant upscaling will be possible. Consider – ion wind lifters have been around for years but we don't use them for daily transport.

### 23 July 2015 – AHE Science Fair

The Auckland Home Educators Science Fair was held today, with some great work amongst the projects. Interesting things learned include: pure water can't form bubbles because surface tension rips them apart; SPI stands for Serial Peripheral Interface; the magnetometer in a cellphone can sense the location of a nearby magnet and tell how it's moving; red cabbage juice is a lot of fun to use testing acids and bases and is something that can be done in your own kitchen.

The NIWA Auckland City Science and Technology Fair 2015 will be held on 20-22 August, so any students entering their projects in that science fair have four weeks to make tweaks and add final touches to their projects.

### 14 July 2015 – Pluto flyby

As New Horizons heads toward its flyby of Pluto (now less than 12 hours away), the dwarf planet has been found to be slightly bigger than previously thought, with a diameter of 2370 km. It was difficult to measure accurately from Earth because of Pluto's atmosphere. Its surface gravity is 0.655 m/s2, or about 1/15 Earth's surface gravity.

Charon's size is confirmed as 1208 km diameter. It was easier to measure from Earth because Charon does not have an atmosphere. Charon is massive enough that the centre of rotation of the Pluto/Charon system is between them, meaning Pluto-Charon can be regarded as a binary system.

Pluto was discovered in February 1930, although it was photographed as early as 1909. Charon was discovered in 1978, and present in photographs dating back to 1965. Nix (about 56 km x 26 km) and Hydra (about 58 km x 34 km) were discovered in 2005. Kerberos (about 31 km across) was discovered in 2011 during a search for rings around Pluto. Styx (8-28 km across) was discovered in 2012 while searching for potential hazards for New Horizons.

### 24 June 2015 – Leap second coming up

Coordinated Universal Time (UTC) is based on the definition of the second in the international system (SI), whereas Greenwich Mean Time (GMT) and its successor UT1 are based on solar mean time. This means the two time standards slowly get out of sync with each other. To compensate, every so often an extra second is added to UTC on either the last day of June or the last day of December.

The last minute of 30 June 2015 UTC will thus be extended by one second. Digital clocks programmed to cope with the leap second will display 23:59:60. New Zealand Standard Time (NZST) is UTC +12:00, so the leap second will occur here immediately before midday on 1 July 2015.

The last time a leap second was added to UTC was 30 June 2012.

### 4 June 2015 – The problem with maths in New Zealand

Today a report was launched criticising the way New Zealand children are taught maths as a result of the Numeracy Project, introduced in 2000. This NZ Herald article says: The project over-complicated teaching ... asking children to learn multiple methods for solving maths problems before learning basic facts, such as times tables, or written methods such as column addition.

This is a serious problem for the students, because not knowing their times tables by the time they get to secondary school is a huge hindrance in continuing to learn. (Multiplication grids can help with learning times tables.)

The article highlights one example showing how serious the situation is: The report ... quoted a 2010 study that found a third of new primary teachers could not add two fractions (7/18 + 1/9). "When teachers can't do simple fractions, that's shocking," said NZI executive director Oliver Hartwich. "Teachers have to take some of the responsibility." Those new teachers were very likely themselves to have been taught under the Numeracy Project.

### 13 May 2015 – North Shore science class for teens

We're looking at starting a science class on Auckland's North Shore for teenagers, probably at 10am on Thursday. Get in touch if you might be interested in this.

### 21 January 2015 – Space dates to note for this year

On 26 January, images of Ceres taken by the space probe Dawn will exceed the resolution of pictures of the dwarf planet taken by the Hubble space telescope. We may get an answer to what the mysterious white dot is. Once Dawn arrives on 6 March it will orbit Ceres and gradually spiral inward, ending with an orbital altitude of 375 km in late November. Dawn will end up in a stable orbit around Ceres.

On about 5 May, images of Pluto from the space probe New Horizons will exceed the resolution of that dwarf planet taken by Hubble. We expect to get lots of answers there. Sadly, New Horizons is travelling too fast to hang around for very long, when it arrives in July.

On 7 May, Mercury will be at its maximum eastern elongation. The innermost planet's recent maximum eastern elongation meant easy evening viewing of it and Venus (which happened to be in the same part of the sky) at the same time. Mercury is worth a look, especially for those who haven't seen it before. Use binoculars or a small telescope if in a city.

### Other News

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