Liquid metal telescope

Posted on 30th August by Mr Reid

As previously mentioned, size matters when it comes to telescopes: the bigger the mirror, the better the telescope (i.e. the greater the resolution and light-gathering capability). The world’s largest single telescope mirrors are the 8.4-metre telescopes used by the Large Binocular Telescope.

Telescope mirrors must be perfectly polished and accurate in shape and size to within a billionth of a metre. This means that making telescope mirrors is extremely difficult and therefore time consuming and very expensive, costing millions of dollars.

But there is an alternative to polished metal and silvered glass: mercury. Simply filling a pan with liquid mercury will create a perfectly flat* reflective surface; the surface can then be made curved by spinning the pan. No expensive manufacturing is required and this keeps costs low: a liquid mirror costs about 1% of the cost of a similar-sized conventional mirror. (They do have the disadvantage that they can only point upwards, however.)

The University of British Columbia’s six-metre Large Zenith Telescope in Vancouver is the world’s largest liquid mirror telescope.

The simplicity of constructing a liquid mirror telescope has even led to suggestions that one should be built on the Moon.

* To give you some idea of how flat a liquid mirror is: if you built a mirror the size of the Earth, the largest bump would be less than a millimetre in height.

Tagged , | Leave a comment

Things From Movies That Cannot Exist Number 2: The Magical Shotgun

Posted on 18th August by Mr Reid

The Magical Shotgun (and it’s close cousin, The Magical Pistol) is a staple of the over-the-top action movie. The Magical Shotgun will be familiar to anyone who’ve ever watched a John Woo film: a character hit by a shotgun blast is thrown backwards at great speed through the air, usually into a plate glass window.

Unfortunately this just isn’t possible and the Law of the Conservation of Momentum explains why: in any collision, whether it’s a car striking a bus, or buckshot striking our leading man, momentum must be conserved. The total momentum before the collision must equal the total momentum after the collision.

Momentum is the product of mass and speed and can be loosely thought of as indicating how difficult it would be to change the motion of something. The graph below shows how momentum changes - a darker background indicates greater momentum.

The momentum before the collision is the mass of the shot multiplied by its speed: using typical values of 30 grams of shot travelling at 350 metres per second we have a momentum of 10.5 kgm/s. After the collision the momentum is the combined mass of the target plus the shot, multiplied by the speed of the target moving backwards.

If we assume the target is an average-sized man with a mass of 85 kg and that he’s standing still before he gets shot then the combined mass is 85.03 kg, which, with a momentum of 10.5 kgm/s gives us a final speed of 0.12 m/s or twelve centimetres per second (0.27 mph); this bears no relation to what’s seen on film.

Tagged , | Leave a comment

How dangerous is it to ride a motorbike?

Posted on 14th August by Mr Reid

Statistics from the Office for National Statistics (via the Department of Transport) and the Motor Cycle Industry Association show that (for the year ending December 2009) motorcyclists make up 2.6% of road users, and 21.2% of road deaths.* So how dangerous is it to ride a motorbike?

This is really a question of quantifying risk, and that’s not something we’re very good at. But let’s take a look at the statistics:

There were 2222 “all road user” deaths in 2009, of which 472 were motorcyclists. If motorcyclists were killed at the same rate as they are present on the road then we would expect only 58 (well, 57.7) of the 2222 dead to be motorcyclists. Can we therefore say that 414 motorcyclists died who “shouldn’t” have died? Can we say that the rate of motorcyclist deaths is 8.14 times what it “should” be?

Looking at death figures says nothing about the ability or skill of motorcyclists. Some would argue that the majority of motorcyclists are killed by the poor driving of car users and not by their own poor driving; but this does not alter the fact that it is the motorcyclists who die.

How likely are you to die on the road?

85.9 people are killed or seriously injured on the UK’s roads per billion motor vehicle miles. That means that if you drove a billion miles (more than eleven times the distance from Earth to the Sun) in one vehicle you would expect 85.9 deaths (or serious injuries) to occur. To put that in more manageable terms, if you drove the UK average of 8000 miles per year you could expect to kill or injure 0.000687 people (per year). To kill or seriously injure one person you would either have to drive 8000 miles per year for 1455 years, three months, five days, twenty hours, forty minutes and thirty-one seconds; or drive 11 641 444 miles per year.

If you started driving at midnight on the morning of 1st January of zero AD you could expect to kill or seriously injure someone (or yourself) by twenty to nine on the evening of 5th March 1455, a month or so before Pope Calixtus III takes over from Pope Nicholas V as the 209th pope (the current pope, Benedict XVI, is the 265th). If you decided to drive the eleven million miles in one year that would require an average speed of 1329 miles per hour, nearly two and a half times the speed of sound.

Whichever way you look at it, you’re pretty unlikely to die on the roads.

But more likely if you’re on a motorbike.

* Doing research for this post I also discovered that in 2008 the DVLA licensed 319 “lifeboat haulage vehicles”, nineteen “mine rescue vehicles” and three “digging machines”.

Tagged , | Leave a comment

Naming element 114

Posted on 9th August by Mr Reid

Element 114 was first created at the Joint Institute for Nuclear Research in Dubna, 120km north of Moscow, by bombarding plutonium-244 with ions of calcium-48. This created an unstable atom of element 114 (indicated by the asterisk) which then decayed into a different isotope of element 114 and three neutrons:

Unq

But what is that symbol - “Unq”? Unq is the current chemical symbol for element 114, known at the moment by its systematic name, ununquadium (“un” - one, “quad” four).

Now that the work by the JINR has been verified by work at the US Berkeley Lab and German GSI laboratory, the International Union of Pure and Applied Chemistry (IUPAC) will invite the researchers from Dubna to submit a “proper” name; this name will then be scrutinised for six months before being approved or disapproved.

Scientists at the Dubna laboratory are already responsible for naming element 102 “nobelium” and element 105 “dubnium” (there was some controversy over this). According to the rules, the discover may not submit a name that has already been proposed for another element so both “kurchatovium” (which Dubna proposed for element 104, after Igor Kurchatov) and “nielsbohrium” (which they proposed for element 105) are out. (Niels Bohr was later honoured by the naming of element 107 “bohrium”.)

Of the ten heaviest named elements, seven are named after people (copernicium, roentgenium, meitnerium, bohrium, seaborgium, rutherfordium and lawrencium) and three are named after places (darmstadtium, hassium and dubnium). Seaborgium is unique in that it is the only element to have been named after someone who was alive at the time of naming.*

Readers at The Guardian have suggested atlantium and salubrium as names, whilst commenters on a post at Physics World (a better crowd, of course) have suggested fibonaccium, darwinium and diracium. What do you think? What should element 114 be called?

* The discovery of einsteinium and fermium (by a team that included Seaborg) was kept secret during the Cold War and thus their names did not become known to the public until after both Einstein and Fermi had died.

Tagged , | Leave a comment

My favourite “proof”

Posted on 5th August by Mr Reid

I have a favourite question in physics:

“Why do things get darker when they get wet?”

This is my favourite question because the proof is so brilliantly simple, and easy to demonstrate.

Objects appear darker when wet because more light passes through them. Brightness is a measure of how much light is reflected to your eyes, and if less light is reflected then more light must be being transmitted through the material (or absorbed).

When wet, water fills in the “gaps” in the material, “channeling” light through it to the other side.

You can prove this is the case by holding a wet piece of material up to the light - it appears brighter than the surrounding material because more light passes through the material to your eyes.

Tagged | Leave a comment

Things From Movies That Cannot Exist Number 1: The Grapple Gun

Posted on 2nd August by Mr Reid

The grapple gun is a staple of the action movie genre: simply point the hook skywards, fire and have the gun lift you onto the roof of your local Abandoned Warehouse™ or Deserted Chemical Plant™. The Batman is particularly fond of the Grapple Gun, making it a staple of his famous Utility Belt.

So let’s look at the physics:

Assuming The Batman is a well-built adult male and that he’s wearing a substantial amount of body armour and equipment, a mass of 150kg is probably reasonable. Raising a 150kg weight to the top of a ten storey (30m) building requires about 45,000 joules of energy (45 kJ). If The Batman takes thirty seconds to do the journey then that is equivalent to a power of 1500 W. A motor capable of lifting The Batman’s 150 kg weight is probably about 75% efficient, meaning the motor has to develop about 2000 W.

If we assume that the grapple gun’s motor is no more than 5 kg in mass (for ease of wielding) that gives a power-to-weight ratio* of 400 W/kg. This is within the capabilities of modern electric motors, but only just. Finding a battery that can provide 45 kJ is not difficult; lithium ion batteries can provide about 600 kJ per kilogram. However, they can’t supply that electricity quickly enough, managing only about 300 W/kg which means that the Grapple Gun’s 5 kg motor is going to come with a substantial 5kg battery to match. Then there’s the weight of the gun itself and the super-strong cable to consider …

Whilst devices for firing grappling hooks do exist (I’m told the Battelle Tactical Air Initiated Launch system is good) and powerful electric motors are fairly common, merging the two to create a useful handheld device is beyond the capabilities of physics at the moment. A real grapple gun would be far too bulky, heavy and unwieldy to be of any practical use.

* Of course this should really be power-to-mass ratio, but I’m going to stick with the more commonly used term.

Tagged , , | Leave a comment

Rods from God

Posted on 31st July by Mr Reid

The problem with bombs is getting them to their target. Dropping them from the air has always been the standard approach (Austrians used air-dropped bombs during the siege of Vienna in 1849), but this is beset by problems. Even stealth aircraft like the B-2 Spirit stealth bomber and the F-22 Raptor stealth fighter are not perfect.

The Rods from God idea did away with aircraft, and with explosives altogether. The concept is very simple: a series of satellites orbit Earth armed with “tungsten telephone poles”. Once a target has been selected and the satellite is overhead, the “pole” is released and pushed towards Earth by a small rocket motor. As the pole falls to Earth from space it requires no fuel; it is powered by gravity alone.

With such a large distance to fall the rod has plenty of time to accelerate, even when the effect of air resistance is taken into account. Hitting the ground at more than ten thousand metres per second (more than 24000 mph) the rod would be able to strike targets buried deep underground.

With a mass of more than eight and a half tonnes, a rod travelling at that speed would have an energy density of fifty million joules per kilogram, far more than TNT (4.6 million joules per kilogram) or nitroglycerin (6.4 MJ/kg). With very little warning of incoming attacks, the weapon’s speed would make it almost impossible to defend against.

Fortunately (or unfortunately, depending on your viewpoint) the Rods from God (or “kinetic bombardment”) system has yet to be deployed. The most recent mention was in a 2003 US Air Force report (PDF) that classified “hypervelocity rod bundles” as a “Post-2015” technology.

Tagged , , | Leave a comment

Uranium-233 and the thorium future

Posted on 22nd July by Mr Reid

When people think of nuclear fuel they tend to think of uranium and plutnonium, or more specifically their fissile isotopes: uranium-235, plutonium-239 and plutonium-241. But there is another fissile isotope that doesn’t get the attention it deserves: uranium-233.

A fissile isotope is one that can sustain a nuclear chain reaction. There is only one naturally-occurring fissile isotope: U-235 which makes up 0.7% of mined uranium (the other 99.3% being non-fissile U-238). Plutonium-239 and -241 are both “bred”, created artificially in a reactor: Pu-239 from the inert U-238 and Pu-241 from Pu-240 which is itself bred from Pu-239.

Making plutonium-239:

In the first stage U-238 is bombarded with neutrons (n) to create U-239. This U-239 then undergoes beta decay* to form neptunium-239:

This neptunium then undergoes a second beta decay to form Pu-239:

Making plutonium-241:

To create plutonium-241 the plutonium-239 from the previous step is bombarded with neutrons to form first Pu-240 and then Pu-241.

Breeding uranium-233 from thorium:

Uranium-233 is produced by bombarding thorium-232 with neutrons to create Th-233 which then undergoes two beta decays to form U-233. This can all be done inside the reactor itself.

Using thorium as a nuclear fuel has a number of significant advantages: it is made up of only one isotope which means that no costly (in both financial and energy terms) enrichment processes are necessary and thorium is at least four to five times more abundant in Earth’s crust than uranium.

Thorium can be used in a molten salt reactor, where it is dissolved into uranium fluoride to form a fluid that is both fuel and coolant (the full name of this reactor is the liquid fluoride thorium reactor). The advantage of using molten thorium as both fuel and coolant is that the reactor then has passive (“fail-safe”) safety: if the fuel begins to overheat then the reaction rate decreases, making a meltdown impossible.

The reaction takes place at a pressure of one atmosphere, meaning no pressure containment vessels are needed. Thorium reactors produce far less waste than uranium reactors do, and the waste produced is far safer: after 10 years 83% of the waste can be sold to recyclers and reused.

More information:

* Completists will notice that I’ve missed out the electron antineutrinos produced in beta decay; I’ve removed them for simplicity since they don’t really play a role here.

Tagged , | Leave a comment

Advert of the year?

Posted on 18th July by Mr Reid

My money is on this for a Black Pencil or a Lion:

In my opinion it’s an outstanding piece of advertising. First I’ll explain how they did it, and then I’ll explain why I like it so much.

In order to make the advert work the balloon has to be neutrally buoyant. A neutrally buoyant object has a mass that is equal to the mass of air (or another fluid) that it displaces. This means that the weight of the object is cancelled out by the buoyant force upon it. There is no overall force on the balloon and it floats neither up nor down.

With no buoyancy or weight forces acting, the balloon responds only to the forces exerted upon it by the surrounding air. Because of the way that the Dyson Air Multiplier works the sucking effect of the “fan” draws the balloon in, and the expelled air then drives it forward. The absence of any blades means that the balloon is able to pass through the fan without harm.

But why is it such a brilliant advert? First, the soundtrack: there’s no voiceover, no actors or actresses, just the sound of the fans themselves. And they are quiet and smooth. One of the things people like least about conventional fans is the noise they make - here Dyson show off one of their fan’s unique selling points without you even realising it.

Then there’s the idea itself: a balloon passing through a fan? The unique selling point of the Air Multiplier is the absence of any blades; a fragile balloon is the perfect test object. If a balloon can pass through a Dyson fan safely then so can your children’s fingers and your pets’ noses.

And lastly there’s the setting. The way that the fans are arranged (carefully set up to show the Dyson’s ability to tilt and rotate) around the offices and manufacturing plant puts you inside Dyson and shows you the sort of company you’re buying from.

I should also point out that this doesn’t seem to be the work of an advertising agency. The disclaimer on the video even goes as far to specify that the advert was “created and executed by trained Dyson engineers”.

Tagged , , , | Leave a comment

How maths is different from science

Posted on 12th July by Mr Reid

“It doesn’t matter how beautiful your theory is, it doesn’t matter how smart you are. If it doesn’t agree with experiment, it’s wrong.”

— Richard Feynman

In science we first observe a phenomena (e.g. the Moon orbiting Earth) - and then come up with a hypothesis (e.g. objects with mass attract each other) to explain it. That hypothesis is then tested by experiment; if the evidence from the experiment contradicts the hypothesis then it is disproved and must be rewritten. If the evidence does not contradict the hypothesis then it is supported, not proved.

All the evidence in the world cannot prove a hypothesis, whereas only one piece of evidence is needed to disprove it. It would only take one instance of something “falling” upwards to disprove the theory of gravity.

In maths the situation is very different: once something has been proved, it is proved forever. No further research is necessary, no tests need to be performed. Pythagorus’s theorum about the lengths of the sides of right-angled triangles has been proved in many different ways (Cut the Knot has 84 different proofs), but will never be disproved.

Tagged , | Leave a comment

Pylon of the Month

Posted on 10th July by Mr Reid

This month’s Pylon of the Month is a beauty, even if it is only an artist’s impression.

Designed by Hugh Dutton Associates for a competition run by the Italian electricity transmission company Terna, the new pylons would cost three times as much as standard pylons, but would still save money by reducing the overall length of the power lines.

Images taken from the HDA flickr stream.

Tagged , | Leave a comment

You know it’s a good lesson when …

Posted on 8th July by Mr Reid

Tagged | Leave a comment

Deepwater Horizon to scale

Posted on 5th July by Mr Reid

I didn’t realise until recently just how deep the Deepwater Horizon drilling rig in the Gulf of Mexico was drilling. They drilled 10683m downwards, 1835 metres further than the height of Mount Everest.

I made this image to show the scale of the drilling; one pixel is equal to ten metres.

Tagged , | Leave a comment

Visualising the Gulf of Mexico oil spill

Posted on 1st July by Mr Reid

Watching news reports of “millions of gallons” and “thousands of barrels” of oil doesn’t make it easy to visualise the true size of the oil spill in the Gulf of Mexico caused by the destruction of the Transocean Deepwater Horizon drilling rig.

IfItWasMyHome.com makes that visualisation easy:

Tagged , | Leave a comment

The Half-Time Kettle Effect quantified

Posted on 23rd June by Mr Reid

The Half-Time Kettle Effect (HTKE) is an oft-reported part of the football season. The idea is very simple: at half-time, a large number of people watching the match will make themselves a cup of tea, using an electric kettle to do so. The HTKE is the resulting “spike” in the demand for electricity that this causes.

The National Grid is kind enough to make realtime demand data available at their website, so I decided to see what happened during the England-Slovenia game today.

Unfortunately the actual numerical data isn’t available yet via the National Grid website, so I’ve had to calculate the data from the graph itself; data is only updated once every five minutes, so that’s also less than ideal.

From the start of half-time at 1545 to peak consumption ten minutes later at 1555 demand jumped by 1235 megawatts to 40314 megawatts, a 3.2% jump. This is equivalent to more than six hundred thousand average (2 kW) kettles, or an average-sized coal or nuclear power station.

Chances are that the spike isn’t due to kettles alone; opening the fridge door for a beer will often cause the compressor to kick in to replace the lost cold air. Microwaving food or turning on the light to go to the toilet are probably also major contributors to the HTKE.

Continue reading →

Tagged , | Leave a comment

The problem with the bulb ban

Posted on 23rd June by Mr Reid

You might not have noticed, but the sale of standard filament lightbulbs has been banned since last September.*

Current proposals are to replace standard incandescent bulbs with more efficient compact fluorescent bulbs. Fluorescent lights work by passing a current through a tube containing mercury vapour. The excited mercury atoms emit ultraviolet photons which then collide with the phosphor coating on the inside of the tube, causing it to emit light (to “fluoresce”) in the visible part of the spectrum.

The problem with this is that some of the ultraviolet light is still emitted (in fact germicidal lamps are basically fluorescent bulbs without the phosphor coating). Many people are sensitive to ultraviolet light and cannot enter rooms lit by flourescent lamps.

People with conditions such as photodermatosis (where exposure to ultraviolet causes swelling, rashes and blistering) and people with photosensitive epilepsy (the 50Hz mains supply flicker is visible from fluroescent bulbs but not from incandescent ones) have been stockpiling bulbs since the ban was announced.

I’m not against the sale of compact fluorescent lightbulbs; in fact I’d like to see them more widely used (especially in place of the inefficient halogen spotlights that seem so popular). What I’m against is removing the consumer’s right to choose.

(If you’re desperate for lightbulbs and you’re wondering, I took the photo above outside of Rugby Electrical, in Rugby.)

* Technically, it’s only the sale of bulbs for household use that’s banned. “Industrial use” is still okay.

Tagged , , | Leave a comment

Abbreviations and full stops

Posted on 21st June by Mr Reid

Which of these is correct?

The correct answer is “Mr Reid”, without a full stop.

When abbreviating a word, if the last letter of the abbreviation is the last letter of the word then no full stop is required. Thus “Saint” becomes “St” and “Doctor” becomes “Dr”; but “Professor” becomes “Prof.” and “Reverend” becomes “Rev.”.

Tagged , | Leave a comment

A BP anecdote

Posted on 17th June by Mr Reid

You might have noticed that BP is in the news at the moment. Some people have accused it of taking a rather lax approach to safety.

Every year I support a team taking part in the Engineering Education Scheme run by the Engineering Development Trust. Our team’s Engineer has always been from BP’s headquarters at Sunbury and last year the “Celebration and Assessment Day” (!) took place there too.

I’ve never taken pupils anywhere that places more emphasis on safety than BP’s offices in Sunbury.

I made the mistake of crossing the road, with the pupils, at somewhere other than one of the designated crossing places and was immediately reprimanded by a member of BP’s staff. Not an officious security guard, just a regular member of staff. Before the kids were allowed to go anywhere at BP they had to have a safety briefing that included the “stair code” - BP’s rules for using the stairs. Everywhere we went in the labs there were boxes with disposable safety goggles.

Anyway, it’s just an anecdote. It doesn’t look like they’ve done as well in the Gulf of Mexico.

Tagged , | Leave a comment

Drill, baby, drill!

Posted on 16th June by Mr Reid

Many in the US, mainly from the Republican side of the political spectrum have used “Drill, baby, drill!” as a mantra for increasing US production of oil, and for less reliance on foreign sources of oil. The absolutely awful Sarah Palin is one of those people.

I’d like to offer the poster below to those that oppose these people.

And another:

Tagged | Leave a comment

How to make an extension cord

Posted on 7th June by Mr Reid

Sometimes the cable that comes with the device just isn’t quite long enough. In most situations you can just make do, but what if you don’t want to? Making a short extension cord isn’t really difficult at all; all the parts shown below are available from any good hardware/electrical shop.

Wiring the plug is well-covered elsewhere on the web so I’ll only comment on wiring up the pins themselves: the easiest way is to insert the stripped wire all the way through until the insulation reaches the screw holding the wire down, and then snip off any remaining copper.

First you need to remove the socket cover.

Make sure that you take the cover and slide it all the way along the wire before you start wiring, otherwise you’ll find yourself wasting time taking it apart and putting it back together again.

Once the cover is off it’s simply a matter of wiring up the pins correctly - blue to neutral (labelled ‘N’), brown to live and green/yellow to the Earth.

Once that’s done simply slide the cover back along the wire and screw everything into place.

Tagged | Leave a comment