Issue 32 - The article on hypothermia P 65

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I blame all that heated kit....

I blame having to ride with no visor on 'that day'...

[DaveCon]

I get a bit lost in the meaning of wind chill factor.

A temperature of around freezing at 70mph feels like -9C but isn't actually, it's still around freezing. You can replicate this by blowing on the back of your hand; it feels cold but the air is coming from your lungs which is at body temperature (hopefully!) so you shouldn't feel anything. You notice the effect of moving air on the surface of your skin which is a result of evaporation. So in theory anything that stops the air touching your skin should help.

Wind chill due to wind itself (as opposed to movement of a body through air) is different and depends on where the air is coming from. For example if it's coming off the backs of Polar bears it's going to be very cold to begin with. It might be a cold day but step into the (biting) wind and it gets much worse because the wind itself is much colder. A bit like measuring temperature in direct sunlight compared to the shade etc but with wind not sun.

So to summarise :S

[catcitrus]

I get a bit lost in the meaning of wind chill factor.

A temperature of around freezing at 70mph feels like -9C but isn't actually, it's still around freezing. You can replicate this by blowing on the back of your hand; it feels cold but the air is coming from your lungs which is at body temperature (hopefully!) so you shouldn't feel anything. You notice the effect of moving air on the surface of your skin which is a result of evaporation. So in theory anything that stops the air touching your skin should help.

Wind chill due to wind itself (as opposed to movement of a body through air) is different and depends on where the air is coming from. For example if it's coming off the backs of Polar bears it's going to be very cold to begin with. It might be a cold day but step into the (biting) wind and it gets much worse because the wind itself is much colder. A bit like measuring temperature in direct sunlight compared to the shade etc but with wind not sun.

So to summarise :S

I think I disagree with your second paragraph--air temp is air temp--with or without wind--actual temps are taken in a special(vented ) enclosure which shields the temp measurement from sunlight and any condensation/evaporation effects caused(enhanced) by the wind-but there are still wet and dry bulb temperatures which account for relative humidity and evaporation effects--if the thermometer says its -9C then the 70 mph wind is also at -9C. However, we are really talking about Newton's law of cooling when we put a warm body in a cold environment--and its all about the temperature gradient at the surface---if there is no "wind" then the gradient is relatively shallow and the warm body loses heat less fast than if there was a wind--which whisks away any "warmish" air next to the body--and you have a steeper temperature gradient and a much greater rate of heat loss down the gradient so to speak--hence the term wind chill, and the relationship to an equivalent much colder STILL air temperature.
The answer is several micro fibre layers to keep that warm blanket of air around you and "shallow" the temperature gradient, and a top layer that keeps the wind out.
ps who is going the Mallory Park Plum Pudding race meeting (Boxing day)--weather permitting?

[DaveCon]

If you open a freezer door you can feel (and often see) the cold air escape, even though you are in a warm room - this is like the wind blowing from a cold area.

Similarly if the air is from a warm area like the sahara, it feels (and is) warm even though it is blowing over your skin effecting the temperature gradient.

Temperature gradient is an interesting point though.

[AndyB]

It's probably getting on for 15 years since I stopped going caving but I'm 99% sure that air always flows out of the cave when the temperature outside is warmer and the only time it flows into the cave is when temperatures are below about 4c outside which kind of backs Daves comment about cold air going towards warmer air.

[picos mestizo]

Well Cold air is Denser than Hot air so the hot air will go up, but which one moves when they mix.....probably they both move!

[-Ralph-]

If you are outside in a wind on a cold day, with no exposed skin except your face, and you take shelter from that wind, you warm up. For instance standing in a bus shelter instead of exposed on the kerb.

If you get stuck in traffic on a motorbike, you often then heat up, but then cool down once you get going again.

So wind chill must have some effect on the outside of a jacket.

Sent from my SM-G900F using Tapatalk

[picos mestizo]

If a hot object (body) touches a cold object (air) then the hot will get cooler & the cold will get warmer untill equilibrium is reached.
Wind is neither hot or cold it's describing a relative air speed. It's the air that has the property of temperature.

[devon john]

couple of years ago coming back from the Dragon,,, Nick (shoeooo) was in a state we pulled in a cafe and got some hot food down him ,,

he lives a different area than us ,,, he told us that when he got home he couldn't get off his bike and his body was blue,,,,he was ill for 5weeks..

i asked him if he was coming the next year but he declined :whistle:

john