This week, another unforgettable contribution from Ian Francis, maths genius, who is brewing up a real blaster of a question.  Take it away Ian, and we mean – take it away… please!

			The combustible potential of flatus (‘farts’, ‘bottom burps’, call them what you will) is legendary. How deserved is this reputation, and could you do anything useful with yours? Like cook a pizza? My first mission was to research the gases actually present. I learn the major gas is nitrogen, which from a culinary point of view is disappointing, as it doesn’t burn. More interesting is the presence of methane and hydrogen which do both burn. Incidentally, the bad smell of farts is due to other substances that are present (fortunately) in small amounts, so won’t trouble me in my calculation. Trawling the Internet, one figure wafts up suggesting that you emit a half litre of gas each day. If we assume that a fifth of this can actually catch fire we have 0.1 litres of potential fuel (4/5ths of regular air being incombustible nitrogen). Now I look up the energy value of this volume of methane in my trusty science data book, which is 3.7kJ. Next I dig out the booklet that came with my Electrolux oven. It’s not fascinating reading, but I learn that the power rating is 2.1 kW (with a few watts here and there for the fan and light). But my pizza box says cook at 200 deg C, and not the 250 deg max that the oven would do on full power, so I scale down the 2.1kW by 80% giving just under 1.7kW. 1.7kW tells me that every second 1.7kJ of electrical energy is transferred into heat by the oven. Giving the pepperoni pizza 15 minutes heating will transfer 1.7kJ x 60seconds x 15minutes = 1530kJ of energy. Nearly there now- a day’s popping off produces only 3.7kJ out of the 1530kJ needed which is only 1/414th of the way there. Or put another way, you’d need to guff from now until November 2007 to get enough fuel to cook the pizza. So despite recent electricity price rises I conclude that it’s best not to cancel my direct debit just yet... Only pedants need read on… I start shakily by trusting numbers trawled off the net- but I reckon ½ a litre sounds about right. ½ of 10 litres (i.e. 5 litres) and you’d have to be careful of sources of ignition I think, and ½ of 0.1 litre (i.e. 0.05l) and we just know you are lying about trumping so little. Basically, the ‘order of magnitude OK?’ box is ticked. To simplify the maths I’ve assumed the only combustible gas present was methane, when in fact there’s hydrogen there too. Your homework is to find out if the energy given off by burning hydrogen is significantly different to that of burning methane and, if so, does it extend or shorten the 1-and-a-bit year time scale?

Thanks Ian. Send in your answers to planet-science.news@nesta.org.uk. Don’t forget to quote MATHSACISE in the subject line. All correct answers who also remember to include their postal address will receive Some delicious chocolate covered Kendal Mint Cake, our traditional Maths prize.

Last week, Angela Pollard wrote:

Making my coffee in the staff room the other morning, I added a spoonful of coffee granules to half a cup of hot milk, only to find that the milk erupted and splashed spectacularly out of the cup. I've since tried to repeat this 'success', with varying results. What was going on?

Well this question produced a flurry of excellent replies whose common theme was – superheating. Declan Fleming says:

“The milk was superheated. Without nucleation sites, bubbles can't form and the liquid can't boil very easily so it can heat above its boiling point without boiling. Coffee granules have a rough surface on which bubbles can form allowing the liquid to boil.” Dr Peter Borrows agreed and also commented:

“How was the milk heated? In a microwave, I bet. Water (and let's face it, milk is mostly water, especially if it is skimmed) can become superheated in a microwave.” Mary Wood says:

“When you superheat milk, its temperature is above the normal boiling temperature. We know this can happen easily whether heating milk in a saucepan or microwave oven as eventually it rises over the top, unless we are quick enough to remove the source of heating.

However, even if we have not yet arrived at the messy stage, the milk can be hotter than boiling. When we add nucleation sites, such as coffee granules, many bubbles of steam may be produced at once shooting up to the top taking coffee and milk with it. This can happen with soups and gravy if there is a layer of fat to stop the steam from escaping.

If there is little fat, or there are other materials in the cup or liquid, the milk may not become superheated so the problem does not occur.”

Thanks everyone. So Angela, now you know and once again the scientist was NOT stumped! Mind you it does sound a little hazardous, an unsuspecting person could get scalded couldn’t they? Spread the word!

On to this week’s question:

“If light travels in straight lines, even when refracted then why are rainbows curved?”

From Paul (Soupy) Campbell
Head of KS4 and Mad (students’ explanation!) Science Teacher
(Planet Science loves mad scientists – teachers or otherwise)

If you can help or if you have a burning question of your own then send us an email with STUMP THE SCIENTIST in the subject line to planet-science.news@nesta.org.uk

You will need:

• Granulated sugar
• Salt
• Teaspoon
• Drinking glass
• Fizzy drink
• Plate

What to do:

1. Pour yourself half a glass of fizzy drink and place it on a plate.
2. Take a teaspoon of sugar and sprinkle it into the fizzy drink.
3. See the bubbles rush up?
4. Now sprinkle in some salt.
5. See the bubbles rush up again?
6. Now throw it away before someone accidentally drinks it. Yuck!

What’s going on?

Well it’s back to that idea of nucleation sites isn’t it? See Stump the Scientist this week.  However in this case there is no danger of scalding yourself. Fizzy drinks contain bubbles of carbon dioxide.  The carbon dioxide is pumped in under pressure.  The carbon dioxide dissolves in the water to form carbonic acid which is a weak acid. When the pressure is removed e.g. when the bottle is opened the carbonic acid starts to revert back to carbon dioxide and water.  Hence the hiss as the drink is opened and the bubbles of gas start to release. When the sugar or salt is sprinkled in they provide nucleation sites.  This means that bubbles of carbon dioxide can stick to the particles and cluster.  Thus more bubbles of carbon dioxide are produced and rush to the surface. It is a physical phenomenon – the nature of the powder or granules makes no difference. Hence the coffee in the milk…

Many famous chemists, such as Robert Boyle, experimented with ways of making carbonated beverages. This was high tech stuff. The addition of CO₂ made the drink slightly acid and tastier and also served as a preservative so the drink would last longer without going bad.

But did he try the diet coke and mentos experiments? If you’ve not seen it already look at these guys.

Explore-At-Bristol is an amazing world of hands-on discovery. With over 170 interactive experiences, special exhibitions and a Planetarium showing seasonal star shows, there is something for everyone!  Combined with Wildwalk-At-Bristol, a living rainforest in the heart of the city, and IMAX Theatre-At-Bristol, showing 2D and 3D films on the giant screen, At-Bristol brings science and nature to life! Oh if only we could go there! Well you can…

We have two Explore-At-Bristol family tickets to give away if you can answer the following question:

Which member of the Solar System recently got downgraded in status from planet to dwarf planet?

a)    Pluto
b)    Goofy
c)    Xena: Warrior Princess

Send your answer in an email with your name and address, and the words EXPLORE in the subject line, to planet-science.news@nesta.org.uk.

For more information about Explore-At-Bristol.

The draw will take place at 5pm on Wednesday 25th October.

Nature Detectives is a fascinating site with plenty of information on leaves and seeds. Make a leaf bag to collect and store all your beautiful autumn leaves.

Darwin Online, Darwin’s Journals and notebooks have been captured and put online – simple as that, so anyone at all can see and read them first hand. 

In Greek mythology, a Chimera is a fire-breathing female monster with a lion's head, a goat's body and a serpent's tail. Something went wrong in the gene pool there then, didn’t it?

Long-nosed chimaeras are rare, deepwater fishes of temperate and tropical seas, living to depths of 2000m. They are larger than the other chimaeras. Their snouts are elongated into cylindrical or flattened points, and they have long tails.

So what are chimaeras exactly? Well they are closely related to sharks, having a similar cartilaginous skeleton. Unlike sharks, their gill slits are covered with a skin (operculum), leaving a single opening on each side. Chimaerids have smooth skins without the dermal denticles of sharks and a single spine in front of their first dorsal fins, which can be laid flat as in bony fishes. Their heads are grooved with lateral lines and their upper jaws are fully fused to their heads, unlike in sharks where the upper jaw is only loosely attached to the skull. Their teeth are modified to form flattened crushing plates with sharp cutting margins; two pairs in the upper jaw, and a single pair in the lower jaw. There is also a club-like frontal clasper on top of the head. All chimaerids are oviparous, laying large eggs in a horny case which is deposited on the bottom. The young do not hatch until six months to a year after the eggs are laid. Fancy waiting that long to see your offspring and then finding that they look like that! Ooh he definitely has his father’s frontal clasper…

What a weird looking creature!

That’s all for this week but remember – if you’ve got anything to add then drop us a line: planet-science.news@nesta.org.uk.We’re open to contributions 24/7.

Have a great week.

If you would like to view the Planet Science Newsletter Archive click: http://www.planet-science.com/about_sy/news/ps_index.html You can read back issues of Wired-Up for younger teens here: http://www.planet-science.com/wired/wiredNL/archive/ Or you can read back issues of Hay-Wire for Under 10s: http://www.planet-science.com/wired/haywired/archive/

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