I appreciate that there are plenty of folk who aren't particularly interested in the science and engineering that relates to activities in the outdoors.  But there are others (including me) who find these topics fascinating. 

So I thought I'd start a topic to deal with science-related questions (about gear, sports science or the outdoors environment in general) in a dedicated thread where we don't have to apologise about hijacking an otherwise straight-forward conversation.

I invite you to fire in your questions and we'll see if the collective knowledge and expertise of OMers can rise to the challenge...

OK, how about this one...

 How come man has not managed to produce an artifical rival to down? We can produce fibres only a few atoms thick, so why cant we produce something like down?

Down has tens of million years' head start!  We're actually doing pretty well by that standard.  Also bear in mind that wool and silk also manage things we're not completely up with as yet.

Onto the really tricky stuff, why is the weather always best when you can't get out in it? 

Pete. 

Peter,

the weather one could be related to the so-called atmospheric Weekend effect. The varying levels of pollution from man-made sources follow the weekly cycle (especially low level Ozone and particulates) and have been shown to affect the local weather.  It seems that pollution actually reduces the precipitation in some areas - so conversely when the pollution is less at the weekend, the weather is worse!

http://www.sciencenews.org/articles/20031011/note13.asp

http://www.pnas.org/cgi/content/abstract/100/20/11225

http://www.rsc.org/chemistryworld/Issues/2003/May/weekend.asp

http://www.sciencenews.org/articles/20000311/fob1.asp

Here's a topical one then, and one I can't find an answer to, despite knowing a farmer!

...Given that foot and mouth is rarely fatal, and can be vaccinated against, why is it necessary to slaughter everything for miles around as soon as it rears it's ugly head?

My idle queries. 

Economics:-

1. Much high quality down comes from eastern europe. Will economic developement there increase labour costs to make it even more expensive than it is already?

2. Merino clothing seems to come from down under -- the material if not the finished garment. I thought that Merinos were originally spanish from the pyranees. Given the parlous state of sheep farming, I would have thought it attractive to produce such a premium product more locally to europe. Oz and NZ are not exactly low wage countries either. Are there any technical reasons for why merino is not farmed here, or is it all to do with the absurdities of CAP?

Genetic engineering:-

 AFAIK engineered crops are restricted to pest resistance and pharmaceuticals. Is anybody working on anything for clothing like growing silk in a vat or wicking cotton? Or indeed artificial down for that matter.

Running hot or cold.-

Why? Is it intrinsic metabolism? Or how fast you go/how often you stop.  

How does this translate in to how much you actually sweat. I'm looking for some numbers to compare against vapour transfer rates quoted for gore-tex and the like.

Here is a paper (PDF link) showing vapour transfer rates for various breathable fabrics. Interesting to note the effect of humidity

Klets have an interesting article comparing synthetic and natural clothing systems - http://www.klets.co.uk/Natural%20vs%20Synthetics%20Report.pdf
 The gist --- they got colder in the natural.

I see tarps being made of spinnaker and cuben fibre. But not full tents. Is there a reason for this? I assume the resulting tent would be pricey, but I would have thought the premium manufactures would have gone for it. What would a TN laser competition weight and cost if it was made of cuben fibre. Would it be as strong as sil-nylon? Anyone shed light on this?

Why should I have a tent? I want a force field. I've seen them on Star Trek. I want one. I want to sit out under an invisible shield, set my phasor on kill and vapourise midges! 

Mick,

I believe that Britain is classified by the World Organisation for Animal Health as a country that is without FMD and without vaccination, which gives it access to the most favourable export markets. So if they wish to maintain this categorisation and deal with the outbreak they are forced to slaughter animals.

Aye, but why is it so BAAAD in the first place?

It aint fatal, it can be cured fairly easily...

I got one...

why is a YAWN contagiouse??

if i yawn you no if you are stood next to me you will yawn too...(maybe im boring)

                                                          ...(()) LIKE MY SPIDERS(()).......

Doesn't F&M render the cow a lot thinner after infection?

Basically, the economic value of the animal is less as there's less meat and/or less milk?

(i'm not 100% tho as i can't be arsed to google!)

pt 1)

Obviously, there are dozens of individual factors that differentiate between individuals, and for a given individual in different circumstances. But some basics are fairly standard.

For all sorts of biochemical reasons, mammals need to maintain their core temperatures within a fine range, known as thermal balance. Thermal balance can only be achieved if the sum of all heat losses is equal to the sum of all heat sources. If these are not balanced you will gain or lose heat. So working out why you run hot or cold is essentially an analysis of inputs and outputs. The inputs are metabolic and environmental. Dealing with response to environmental heat would be lengthy and isn’t that relevant to most UK conditions. So we’ll assume that you are the only source of heat in a cold environment and concentrate on the metabolic aspects.

Almost all the exercise related to walking is aerobic – that is to say, you are using an efficient energy source at low intensity for long periods of time. Aerobic capacity is approximately proportional to the surface areas involved – the lungs; the capillaries; the muscle fibres etc. So roughly speaking, aerobic energy capacity will be proportional to the square of a person’s height and (equivalently) the mass of a person raised to the 2/3 power. However, the effort required to climb a hill will approximately scale with that person’s mass. So, intuitively, the heavier person will have to work proportionately harder (at a higher percentage of aerobic capacity) to climb, generating more heat.

Worse still, the rate at which a person can lose heat to the environment is also related to surface area. A heavy person generates more energy to climb a hill, but also has a lower surface area to mass ratio. So for a given metabolic energy load, the core temperature will increase more and will take longer to cool down. This is even worse if the body type is closer to spherical (no insult intended) as the surface area to mass ratio is even lower and there is more to insulate the hot body core and muscles from the cooling air. In the natural world, this is why small creatures tend to have thick fluffy fur (e.g. rabbit) compared to larger creatures (e.g. elephant or cow).

Basal metabolic rate is important too when you consider heat generation at rest. This decreases with age in adulthood, partially explaining why the elderly suffer worse from the cold. But given that it takes about the same energy to lift a 70kg man to the top of a mountain irrespective of age, there another important factor : economy. In aerobic exercise, only about 20-30% of the energy generated is used for muscular movement; the rest must be lost as excess heat. But a trained individual makes more efficient use of their muscles too, so will work less hard for a given task. Anyone who has taken up running for the first time will notice that within only a few weeks they are able to run more comfortably at a given pace. Most of this initial change is down to improved economy of motion rather than improved cardiovascular fitness (which takes longer to develop).

pt 2)

Once you have started to heat the body core, you will trigger physiological responses to lose heat. The first is called peripheral vasodilatation – the body directs more blood to the vessels just under the skin surface. This raises the skin surface temperature and accelerates heat loss by radiation, convection and conduction. But passing the blood through all these tiny vessels is an additional stress to the heart, so if you continue to exercise while hot, your heart rate will rise for the same effort level and you will be generating even more heat.

The likelihood is that the vasodilatation won’t be enough to compensate for the heat load, so the next response is sweating. Once again we are looking at an effect that depends on surface area (larger builds being at a disadvantage). But sweating rates vary a lot between individuals. Generally speaking, fit people who have trained in the heat will produce a less salty sweat that works more efficiently and costs them less in terms of dehydration. But they will also be able to sustain higher sweat rates for longer as the eccrine glands can be trained to endure too.

So if you are hill-fit, lean, of slight build and are well rested & nourished, the chances are that you’ll generate significantly less heat on a climb than a walker of the same age who is rotund, heavy-set and untrained. It’s common sense, but stems from a large number of interacting physiological effects.

pt 3)

I did some rough calcs relating to the need for underarm zips in waterproof clothing here:

Typical sweat rate during exercise in warm weather : 1 litre per hour

Typical body surface area of adult male 1.8-2.0 square metres.

Hence approximately 500 ml/(square-metre x hour)… or 12 000 ml/(square-m x day).

Obviously this is averaged over the whole body and there are places where sweating is much more profuse. Generally I think it is fair to say that the chest, back and underarms sweat much more than the legs, so this kind of transpiration rate is on the low side for an un-vented jacket.  The reality of transpiration rates achieved in lab testing of waterproof/breathable fabrics is hard to come by. But I’ve previously looked at the set of results you posted above ( by the US Army Soldier Systems Center ). They used a humidity gradient of 50% across these fabrics at 30C and at various different internal & external relative humidities e.g. 65% rh ‘inside’ / 15 % rh ‘outside' 

Of the well-known fabrics, eVent performed better in ‘breathability’ across the board but in their tests, never exceeded about 5500 ml / (square-m x day). The maximum they measured for GoreTex XCR was around 4000 ml / (square-m x day), but only when there was high humidity on both sides of the membrane.

Of course, these are quite artificial conditions, but serve to illustrate the huge difference between what is really required during steady exercise (upwards of 12 000) and what is achieved by the best of the current laminate shells (around 5 000).  This is why venting is so important. If you can’t transfer enough vapour through your shell, you need to bypass it or you will inevitably wind up damp. Pit zips have their flaws, but until the fabrics get a lot better, I will still be looking out for them.

pt 3.2! )

of course the best way to keep your clothing dry is to avoid sweating. Take off insulation before overheating and keep it dry for when you need it later!

which came first the chicken or the egg.

In a running race the chicken would probably come first.

In Evolutionary terms, the Egg came first and was utiziled by many species millions of years before birds and poultry evolved.

In a parent to child relationship, the egg also came first, as the egg housed the mutant child that became the founder member of the new species that we call chickens, the parent not being a chicken but a very slightly different species.

PROBABLY, although I have been known to talk utter crap on occasions.