Question of the Week - Old Version

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Offline bezoar

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Re: Question of the Week - Old Version
« Reply #100 on: 11/01/2004 03:42:28 »
Can they sense your breathing changes from another room?  If so, that would explain why my kids didn't begin sleeping all night until they were about 12 or 13.  I'm not much of a sleeper and awaken frequently during the night.  It would be interesting to study if babies who sleep all night long from the time they come home from the hospital have mother's who are heavy sleepers.

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Offline NakedScientist

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Re: Question of the Week - Old Version
« Reply #101 on: 15/01/2004 18:04:22 »
This was quite a tough question.

The answer probably lies in the fact that dreaming occurs when you are in a state of near-wakefulness. Events from the environment can therefore intrude into your dream and even participate in it. Everyone must have experienced the hilarious situation of talking to someone who is asleep. They have no recollection afterwards of what was said, unless they wake up mid conversation.

As to why you wake up and then hear the alarm, giving the impression that you pre-empted the alarm clock, I think there are many possible explanations. You could geuninely have woken up before the alarm because your body-clock has become accustomed to you getting up at that time that it woke you up automically. Alternatively, and this is the explanation I favour, you were dreaming when the alarm went off. In that split second the alarm got incorporated into your dream. As our sense of time is totally skewed when we dream you have no concept of when you really woke up, and when the alarm really started going off.

A hard nut to crack, but still a great question.

TNS

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Offline NakedScientist

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Re: Question of the Week - Old Version
« Reply #102 on: 15/01/2004 18:05:48 »
THIS WEEK'S QOTW :

"IF ALL THE PASSENGERS ON AN AEROPLANE SUDDENLY JUMPED INTO THE AIR AT THE SAME TIME, WOULD THE PLANE MOMENTARILY WEIGH LESS ?"

Have a go, below :

TNS

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Offline Quantumcat

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Re: Question of the Week - Old Version
« Reply #103 on: 16/01/2004 07:42:18 »
That's just like a question that was on this old maths competition thing. the question was, there's a guy that's a juggler that wants to cross a bridge that can only hold a certain weight, and him and the bazlls weigh over it but him and one ball is enough to get by, the question was if he always has two balls in the air can he cross safely.

It does sound like one of those questions, I know the nswer is that it would weight exactly the same, but I'm not exactly sure why. Well the passengers are not 'the plane' so the plane would weigh the same, but I don't think that's really the issue. hmm. I'm sure it has a lot to do with the diagrams of vectors pointing all over the place that my physics teacher just loves drawing. I can just imagine one now ... there's be P pointing downwards from the middle of the plane, something pointing upwards for the thing that keeps the airplane up, lots of P's for the passengers' weights, and lots of R's pointing up for the reaction de support. But come to think of it, if you say 'would the plane momentarily weigh less" you probably mean the plane and the passengers' weights combined right? So on the ground it'd be the same but instead of the vector for the thing that keeps the plane in the air there'd be a big R for the reaction de support of the ground. and when the passengers jump, they'd have to, like, push on the plane a lot to get themselves up off the floor, so the diagram with them pushing off would be a vector pushing down for each, a vector pushing up that would carry them up, their weight, and their reaction de support. The diagram with them in the air would be with their weight and the vector pushing them up then on the way to the ground it would be just their weight. When they're on the floor just as they jump I suppose their reaction de support's would be bigger than before they pushed off. So, in conclusion, I suppose the combined weight would be bigger as they pushed off (but the R's bigger so the plane doesn't, like, move underground or whatever) then the P would just be of the plane, then when they land it'd be the same again except maybe that the landing of the passengers would induce some movement of the plane and make the combined weight go up again for a short time until the movement of the passengers towards the earth had stopped, by the R's going upwards?

I don't know if that's how it's meant to be answerd but that's just a try.

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Offline cuso4

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Re: Question of the Week - Old Version
« Reply #104 on: 16/01/2004 08:42:27 »
At the instant when all the feet of the passengers leave the floor of the aeroplane, the overall reaction  should decrease but then all the passengers are still experiencing gravitational pull so the overall weight shouldn't change.

Not the most straight forward question, I'll have to think about it again.

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Offline Quantumcat

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Re: Question of the Week - Old Version
« Reply #105 on: 16/01/2004 15:02:31 »
what do you mean by 'the overall reaction will decrease'? with the gravitational pull, it's giving them acceleration back towards the plane, but it is only applied to the passengers while they're in the air, not to the plane right? Please tell us the answer NS!

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Offline tweener

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Re: Question of the Week - Old Version
« Reply #106 on: 16/01/2004 19:45:28 »
Last night I wrote a long response to this and my computer crashed before I got it submitted.  Here is a short version.

The average weight of the plane and passengers, averaged over the whole "jump" would remain constant.  On a finer timescale: The weight would start as the combined weight of the plane and passengers. Then, as they jumped, the "weight" would increase to accelerate them upward.  While they were off the floor of the plane the weight would decrease to just the weight of the plane. Then, when they hit the floor of the plane the weight would again increase a lot to decelerate them. Finally, the weight would come back to the "normal" weight of the plane and passengers after they got back to the floor.


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Offline Quantumcat

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Re: Question of the Week - Old Version
« Reply #107 on: 17/01/2004 08:58:00 »
whoo!

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Offline notnakeeinappalachee

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Re: Question of the Week - Old Version
« Reply #108 on: 21/01/2004 14:57:15 »
The plane weighs the same.  The weight of the plane plus its contents, however, is greater when its contents are in contact with its floor.  

 

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Offline chris

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Re: Question of the Week - Old Version
« Reply #109 on: 21/01/2004 16:54:42 »
But what about the fact that the plane is sealed (pressurised) - does this make a difference ?

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Offline bezoar

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Re: Question of the Week - Old Version
« Reply #110 on: 22/01/2004 21:58:17 »
Shouldn't the pressurization of the plane, in itself, increase the weight?
 

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Offline tweener

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Re: Question of the Week - Old Version
« Reply #111 on: 23/01/2004 05:24:34 »
The overpressure of the air would increase the weight a little.  Probably a few milligrams for the amount of pressure in a plane.  Of course it depends on the size of the plane.


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Offline NakedScientist

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Re: Question of the Week - Old Version
« Reply #112 on: 26/01/2004 12:42:03 »
ANSWER TO "WHAT HAPPENS TO THE WEIGHT OF A PLANE IF ALL OF THE PASSENGERS JUMP INTO THE AIR SIMULTANEOUSLY ?"

This was a tough one. Tweener's answer is correct in that in order to accelerate themselves off the floor of the plane the passengers must apply a force and hence the plane will transiently increase in weight. Whilst the passengers are airbourne their weight is no longer pushing down on the plane so it rebounds upwards. Then as they land again their weight is added to that of the plane and the total masss returns to the starting value.

TNS

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Offline NakedScientist

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Re: Question of the Week - Old Version
« Reply #113 on: 26/01/2004 13:26:21 »
Here's this weeks QOTW :

"HOW FAST IS THE EARTH SPINNING ON ITS AXIS ? HAS IT ALWAYS TURNED THIS FAST ?"

TNS

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Offline Quantumcat

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Re: Question of the Week - Old Version
« Reply #114 on: 26/01/2004 15:11:25 »
I have no idea how fast, but I remember the teacher saying in astronomy three years ago that it spun really fast when it was formed and is slowing down.

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Offline Quantumcat

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Re: Question of the Week - Old Version
« Reply #115 on: 26/01/2004 15:12:09 »
I have no idea how fast, but I remember the teacher saying in astronomy three years ago that it spun really fast when it was formed and is slowing down.

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Offline Donnah

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Re: Question of the Week - Old Version
« Reply #116 on: 26/01/2004 20:54:00 »
According to Gregg Braden the earth's magnetics are decreasing and frequency is increasing.

Not sure about how fast the earth is spinning, but guess you could work it out using the circumference of the planet and a 24 hour time period.
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Offline roberth

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Re: Question of the Week - Old Version
« Reply #117 on: 27/01/2004 02:31:00 »
Earth currently rotates at about 1,609 km/h. I don't know if this is constant.
« Last Edit: 27/01/2004 02:51:13 by roberth »
 

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Offline notnakeeinappalachee

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Re: Question of the Week - Old Version
« Reply #118 on: 27/01/2004 16:40:38 »
Pertaining to the last question--weight is due to gravity, which is the force of attraction exerted by the mass of two bodies.  In the case of the airplane, the two bodies are the plane and the earth.  The slight increase in earthward force (and acceleration) exerted when the people push downward in order to jump is not due to the pull exerted by earth and therefore is not an element in the plane's weight.  

Never was much for angular momentum and its relatives.
 

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Offline chris

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Re: Question of the Week - Old Version
« Reply #119 on: 27/01/2004 22:53:37 »
I think that's what they are getting at by referring to "pedants" - it is assumed for the sake of simplicity that the word "plane" refers to the entire system i.e. the plane, the air it contains, and the passengers.

Anyway, what abou this earth rotation question ?

Chris

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Offline bezoar

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Re: Question of the Week - Old Version
« Reply #120 on: 28/01/2004 02:52:20 »
How fast the earth spins might depend on where on earth you are.
 

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Offline roberth

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Re: Question of the Week - Old Version
« Reply #121 on: 29/01/2004 00:33:01 »
OK, then, 1,609 km/h at the equator.
 

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Offline pipster

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Re: Question of the Week - Old Version
« Reply #122 on: 02/02/2004 14:57:22 »
The earth and all the other planets in the solar system are spinning because of the resultant angular momentum from their formation billions of years ago. As the clouds of dust and gas came together under gravity, the matter they contained was pulled in closer and closer until finally the planet we now live on was formed.
Just as when an ice skater spinning on the spot goes faster when they pull their arms in (try it on a swivel chair) this gas contraction increased the angular momentum that causes our days and nights to come round every 12 hours (at the equinox).

Like all systems, energy is lost over time (like a pendulum eventually comes to rest vertically) and so the rotation about our axis is decreasing. This will eventually increase the length of the day since more time will be spent in or out of sunlight at anytime.

Velocity of rotation of a point about an axis (in this case angular momentum) = 2xpixr/24hours
At the north pole where the distance to the centre of rotation could be close to zero, you will have zero angular momentum and it increases up to the equator.

IF the earth spinning around on its axis slows down enough, days will get longer and longer and eventually the length of a day might over take the length of the year, which I believe is what has happened to Mercury?
 

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Offline Ultima

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Re: Question of the Week - Old Version
« Reply #123 on: 06/02/2004 12:54:21 »
The Earth wobbles on its axis wouldn't this effect the speed a tiny bit?
« Last Edit: 06/02/2004 12:58:37 by Ultima »
wOw the world spins?

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Offline roberth

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Re: Question of the Week - Old Version
« Reply #124 on: 09/02/2004 00:25:15 »
C'mon TNS. You should rename this topic "question of the fortnight".
 

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Offline neilep

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Re: Question of the Week - Old Version
« Reply #125 on: 09/02/2004 15:57:25 »
As a kid, I used to think the wind was caused by the Earth spinning faster that day !!!!....

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Offline Quantumcat

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Re: Question of the Week - Old Version
« Reply #126 on: 11/02/2004 15:21:43 »
Lol!! That's so cute! I remember thinking it was caused by convection before I learnt about pressure and stuff.

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Offline NakedScientist

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Re: Question of the Week - Old Version
« Reply #127 on: 21/02/2004 07:33:38 »
Answer to HOW FAST IS THE EARTH SPINNING ? IS THE RATE CHANGING ?

The earth completes 1 revolution per day (24 hours). The distance that it effectively travels (at the equator) in completing 1 revolution is equal to the planet's circumference or girth.

You can calculate the circumference of a circle using the formula 2x pi x radius of the circle.

The radius of the earth is 3963 miles (6378 kilometres). The circumference is therefore 2 x 3963 x 3.141 (approx. value of pi) = 24900 miles (40,000 km)

The speed of the earth is therefore 24900 / 24 = about 1000 miles per hour (1600 km per hour).

The rate of rotation is indeed slowing down. About 65 million years ago, at the time of the dinosaurs, the earth span much more quickly meaning that a day was correspondingly shorter, lasting only about 16 hours.

It is worth bearing in mind, however, that the calculation above applies at the equator - the actual speed you would be travelling at varies according to where you stand on the planet surface - at the north pole, for instance, your speed would be zero. In the UK and north US your speed is closer to 700 - 900 miles per hour (1125-1450 kilometres per hour).

sorry this took a little while to come out - I've been a bit busy !

TNS

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Offline NakedScientist

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Re: Question of the Week - Old Version
« Reply #128 on: 21/02/2004 09:01:49 »
Here's this week's QOTW :

"WHAT IS A SUNSPOT ? WHAT CAUSES THEM AND WHAT EFFECTS CAN THEY HAVE UPON EARTH ?"

TNS

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Offline cuso4

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Re: Question of the Week - Old Version
« Reply #129 on: 24/02/2004 08:39:11 »
Astronomy is never my strong point. I'll have to do some research for this.

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Offline CsManiacDan

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Re: Question of the Week - Old Version
« Reply #130 on: 29/02/2004 20:32:37 »
I'm pretty sure a sun spot is an area on the sun that's cooler than the rest of it, that's why it's darker, though why it's cooler i have know idea nor do I know whats causing it

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Offline neilep

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Re: Question of the Week - Old Version
« Reply #131 on: 29/02/2004 21:17:28 »
Yep...Im with you on that one Dan, I'm sure magnetism comes into the equation too somewhere along the line, as well as the eleven year cycle, where they pop up the most and last about a week or so. Not too sure what effects they have upon the earth apart from manifestations arising from magnetic disruptions ? perhaps electrical disruption and interference with satellite communications, and birds/sealife/animals that depend on the earths magnetic field for navigation.

Or is it just something that adolescent stars get as they go through puberty ? :-)


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Offline Donnah

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Re: Question of the Week - Old Version
« Reply #132 on: 02/03/2004 04:07:20 »
I vaguely remember hearing something about sun spots and radioactivity.
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Offline NakedScientist

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Re: Question of the Week - Old Version
« Reply #133 on: 02/03/2004 05:48:55 »
ANSWER TO LAST WEEK'S QOTW "WHAT ARE SUNSPOTS AND HOW DO THEY AFFECT THE EARTH ?"

Sunspots are dark spots, up to 50,000 miles in diameter, that move across the surface of the sun, expanding and contracting as they go. They usually last for several days, although very large ones can persist for several weeks.

A typical sunspot comprises a dark region called the umbra, surrounded by a lighter region known as the penumbra. They appear relatively dark because the surrounding surface of the Sun (called the photosphere) is about 5500 degrees C., while the umbra is a chillier 3480 degrees C.

Sunspots are surrounded by an intense magnetic field over 2,500 times stronger than Earth's, which is much higher than anywhere else on the Sun. This powerful magnetic field slows down the flow of hot gases from the Sun's interior to the surface, which is why sunspots are relatively cooler than the rest of the sun's surface. They usually occur in pairs which have their magnetic fields pointing in opposite directions

People have been watching sun spots since Galileo Galilei first described them in the early 1600s, and we probably knew about them even before that. There are reports of ancient peoples noticing the sun's blemished appearence, particularly on cloudy days and during dust storms.

But thanks to Galileo's work we now know that the sun follows an 11 year cycle - the Solar Cycle - during which the number of sunspots steadily increases to a maximum, then decreases again at the end of the cycle. Towards the maximum the sunspots occur closer to the equator of the Sun. Plotting the area covered by sunspots at a given latitude versus time produces an interesting butterfly shaped distribution of unknown significance.

Some studies have suggested that the average ocean temperature increases and decreases, world-wide, by 0.5 degrees C in phase with the sun spot cycle, but the mechanism is not understood.

So how do sunspots affect the earth ?

This is not known for certain. During periods of maximum sunspot activity scientists have recorded a very slight increase in the energy output from the sun, and ultraviolet (UV) radiation increases dramatically which can affect our atmosphere. Also, a period known as known as the Maunder Minimum, during which there were very few sunspots, coincided with a number of long winters and severe cold temperatures (called the Little Ice Age) in Western Europe.

Furthermore, sunspots are also associated with phenomena called CME - Coronal Mass Ejections or solar flares. These stellar convulsions produce as much energy as a billion megatons of TNT and occur near to sunspots on the dividing line between the pair of oppositely directed magnetic fields. Solar plasma interacting with the strong magnetic field is ejected away from the sun's surface and out into space forming the flare which bathe the earth in cosmic radiation leading to an increase in geomagnetic storms which can affect satellites, power grids and radio transmissions. They also produce a more pleasant side effect - the beautiful northern and southern lights - where the charged particles interact with the earth's magnetic field...

Some sunspots :


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Offline NakedScientist

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Re: Question of the Week - Old Version
« Reply #134 on: 03/03/2004 02:13:05 »
Here is this week's question of the week :

"CAN YOU EXPLAIN 'WIND CHILL FACTOR'" ?

TNS

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Offline Quantumcat

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Re: Question of the Week - Old Version
« Reply #135 on: 03/03/2004 09:17:59 »
I think so. Wind chill factor is when lots of bits of moisture in the air go past your skin fast, taking heat as they go. Or maybe it's not moisture it's air. Oh well, doesn't matter. That's why you're cold when you get out of the bath too, because the water becomes a thin layer and the abundant heat in your skin goes into the water and it evaporates. All the heat moving out of you makes you feel cold. Also why fans that push air around make you lose heat and feel cooler.

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Re: Question of the Week - Old Version
« Reply #136 on: 11/03/2004 19:40:29 »
I think I have to agree with Quantumcat, but I'm not sure if it's moisture in the air, or air molecules themselves, that cause the decrease in temperature, because (I think) it's possible to have a windchill when there's very little moisture in the air.

Just my 2 cents.

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Offline tweener

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Re: Question of the Week - Old Version
« Reply #137 on: 11/03/2004 20:35:42 »
Moisture in the air (aka relative humidity) affects the wind chill factor by making the air capable of holding more heat for a given volume.  At the boundary between skin and air, there is a layer of still air that warms up and serves to insulate the skin from losing more heat.  When wind moves the air, this layer is thinned and cooled, thus increasing the rate  of heat loss.  The faster the wind blows the faster the heat is lost, thus the wind chill temp. is lower.  The higher the relative humidity, the more efficiently the air removes heat from the skin, and the lower the wind chill temp.

Sounds good anyway.

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Offline NakedScientist

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Re: Question of the Week - Old Version
« Reply #138 on: 14/03/2004 02:00:21 »
ANSWER TO LAST WEEK'S QOTW "CAN YOU EXPLAIN 'WIND CHILL FACTOR'"

You have all pretty much hit the nail on the head. Heat leaves our bodies, which are much warmer than the surroundings, by following a thermal gradient (hot to cold). The cooler the surroundings relative to body temperature, the steeper the gradient and hence the greater the rate of heat loss.

When you stand in still air, heat leaving your body warms the air around you so that it acts like a layer of insulation. This effectively reduces the thermal gradient, slowing down heat loss. But when you are out in a high wind the air around your body is continuously being replaced with fresh cold air. Under these circumstances the thermal gradient becomes much steeper and you lose heat much more rapidly, at a rate equivalent to the surrounding temperature being much colder than it really is. Hence the term "wind chill factor".

TNS
« Last Edit: 14/03/2004 02:12:00 by NakedScientist »

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Offline NakedScientist

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Re: Question of the Week - Old Version
« Reply #139 on: 14/03/2004 02:01:34 »
This week's QOTW is much more challenging and might require a bit of research on your part, but has a satisfying answer. Have a go at :

"WHY ARE THERE 7 DAYS IN A WEEK, AND WHY DOES THE WEEK BEGIN ON A MONDAY ?"

Happy hunting

TNS
« Last Edit: 14/03/2004 02:10:41 by NakedScientist »

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Offline nilmot

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Re: Question of the Week - Old Version
« Reply #140 on: 15/03/2004 08:27:56 »
I'm not so sure this is a scientific question. More of a philosophical question.

Tom
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Offline NakedScientist

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Re: Question of the Week - Old Version
« Reply #141 on: 15/03/2004 23:04:58 »
No, it is definitely a scientific question, with a scientific answer, though some of the answer has its origins in philosophy.

TNS

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Offline cuso4

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Re: Question of the Week - Old Version
« Reply #142 on: 17/03/2004 13:40:39 »
I found something on the Internet which might be what we're looking for.

Why are there 7 days in a week?

One month is roughly the time taken for the Moon to rotate the Earth once. One year is 365 days and divide this by 12, we get 30.416 days per month. One week is the time taken for the Moon the a quarter of the Earth. So divide 30.416 by 4, we get a value around 7.

I'm not sure anout the second question but I'll have a go.
Monday is named after the Moon and since ancient people use the movement of the Moon to measure time (Chinese Calender is based on this), Monday is set to be the first day of the week.

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Offline NakedScientist

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Re: Question of the Week - Old Version
« Reply #143 on: 19/03/2004 05:19:39 »
Well done Angel, you are on the right lines. Keep going.

TNS

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Offline neilep

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Re: Question of the Week - Old Version
« Reply #144 on: 19/03/2004 13:32:48 »
Here is something I have blatantly 'borrowed' from a website I found which I think part explains why Monday is the first day of the week.

MONDAY
There are some countries which have Monday as the first day of the week. This is in accordance with the International Standard
"ISO 8601:1988 (E)"
Which states under item:
5.4 Combinations of date and time of day representations
3.0 Terms and Definitions
3.17 Week Calendar
"A seven day period within a calendar year,
starting on Monday and identified
by the ordinal number with in a year....."

There are countries in Europe, such as Denmark, Norway and Sweden that have Monday as the first day of the week.
In the USA documents ANSI (X3.30) and NIST (FIPS 4-1) adopted ISO 8601 and list Monday as the first day of the week.
However, the calendar in USA has
Sunday as the first day of the week


'Men are the same as women...just inside out !'
Men are the same as women, just inside out !

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Offline neilep

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Re: Question of the Week - Old Version
« Reply #145 on: 19/03/2004 13:37:32 »
Here is something else i have borrowed, regarding the number of days in the week.
Known as an interval between Market Days. In central Asia five days was used, Egyptians used ten days and the Babylonians like the multiple of seven because of the lunations of the moon. In Rome the eight day cycle was used for market. The orgin of the seven day week seems to be related to the four (about) seven day phases of the moon. Also the seven colors in the rainbow, and in the Babylonian times, the seven planets. By the time of the first century BC the Jewish seven-day week seems to have been put into place throughout Rome.


The calendar in the USA has Sunday as the first day of the week. The word week comes from Latin "vicis" meaning change. The week is a period of seven days and is now used throughout the world as a division of time. History seems to favor the Hebrew or Chaldean origin and the week is mentioned as a unit of time in the Bible, see the Old Testament book of Genesis 29:27.
....do me and Angel get a gold star ?

'Men are the same as women...just inside out !'
Men are the same as women, just inside out !

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Offline tweener

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Re: Question of the Week - Old Version
« Reply #146 on: 19/03/2004 16:13:09 »
If you're going to insist that Monday is the first day of the week despite every calendar in the known universe, then I say Monday is the first day of the week so that everyone can get off to a really rough start every seven days. [:)]

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John - The Eternal Pessimist.
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John - The Eternal Pessimist.

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Offline neilep

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Re: Question of the Week - Old Version
« Reply #147 on: 19/03/2004 17:06:54 »
Personally..I think Mondays should be cancelled [:D]

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Offline Donnah

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Re: Question of the Week - Old Version
« Reply #148 on: 19/03/2004 21:16:12 »
I've got it!  It's divine intervention that caused the 7 day week and the week to begin with Monday.  We're told that God made the world in six days and took the 7th day to rest, calling it the sabath.  How do you like that?  He takes the 7th day to rest but expects us to get up on that day to go to church.  *tongue in cheek*
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Offline nilmot

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Re: Question of the Week - Old Version
« Reply #149 on: 20/03/2004 08:45:27 »
But isn't that a religious explaination not a scientific explaination?

Tom
Tom