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Author Topic: Question of the Week - Old Version  (Read 178932 times)

Offline NakedScientist

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Re: Question of the Week - Old Version
« Reply #250 on: 28/01/2005 09:16:57 »
ANSWER TO "WHY DOES ICE FLOAT, WHEN MOST SOLIDS ARE HEAVIER THAN LIQUIDS ?"

Tups and Neil have this correct.

Water molecules resemble tiny boomerangs with an oxygen atom at the centre, and 2 hydrogens for arms. Because the oxygen likes electrons it pulls the electrons of the hydrogen atoms towards it, making the arms of the boomerang slightly positive, and the oxygen slightly negative.

This makes the molecules 'sticky' due to a process called hydrogen bonding. The slightly positive hydrogen from one water molecule is attracted to the slightly negative oxygen of another water molecule, and the 2 try to get closer together.

As you cool down water, the molecules lose energy, slow down, and can pack together more tightly. At 4 degrees C the molecules are at their most tightly packed.

But if you lower the temperature further it becomes more energetically favourable for the water molecules to arrange themselves into a more open tetrahedral lattice, in which each water molecule has a relationship with 4 others.

This configuration, rather like Swiss cheese, has lots of holes between the molecules and so the only way to pack in all the water molecules as freezing occurs is to make a crystal that takes up more volume than the starting liquid.

So why does it float ?

This is down to the Archimedes principle. When you place an object in water it displaces a volume of water equivalent to its weight. In other words water molecules push upwards on it with a force equal to the weight of the water that has pushed out of the way (displaced).

As ice is 'holey', as outlined above, it is much less dense than liquid water (about 9% less dense in fact) meaning that it doesn't have to sink very far before it has displaced enough water to support itself (because the deeper you go the higher the pressure and hence the higher the density).

As a result ice floats - thankfully - otherwise fish would be in real trouble, and the floors of our oceans would be covered with ice...

TNS
« Last Edit: 28/01/2005 09:19:08 by NakedScientist »
 

Offline NakedScientist

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Re: Question of the Week - Old Version
« Reply #251 on: 28/01/2005 09:22:11 »
Here's this week's QOTW

"HOW DO WE KNOW HOW FAR IT IS TO DISTANT GALAXIES - SUCH AS THE ANDROMEDA GALAXY WHICH IS 3 MILLION LIGHT YEARS AWAY ?"
 

Offline nilmot

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Re: Question of the Week - Old Version
« Reply #252 on: 28/01/2005 09:31:27 »
Just some chemistry fact about what 'NakedScientist' said above.

'The oxygen likes electron bit', the technical term is electronegative. Definition is the ability for a covalently bonded atom to draw a pair of electron toward itself. I think saying likes electron can be slightly misleading, some might mis-interpret it thinking atoms have preference to which electrons they like.

Tom
 

Offline neilep

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Re: Question of the Week - Old Version
« Reply #253 on: 28/01/2005 11:29:25 »
I won't answer this cos I'm proud to say I know the answer thanks to Dr Chris and Radio 5 Live :-)

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Offline NakedScientist

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Re: Question of the Week - Old Version
« Reply #254 on: 08/02/2005 13:05:27 »
I'm sad that no one wants to have a go at this week's QOTW...:(
 

Offline Ultima

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Re: Question of the Week - Old Version
« Reply #255 on: 08/02/2005 13:19:22 »
Erm... Don't you take an observable object with known brightness within the Galaxy such as a supernova or I remember something about Cepheid Variables that have fixed intensity for their period which you can use, then using loads of rules of distance r and light intensity etc. you can work out the rough distance??? Or is this just rubbish? I'm guessing... my Astronomy module was a while ago :D

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Offline nilmot

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Re: Question of the Week - Old Version
« Reply #256 on: 10/02/2005 08:55:09 »
Is it the Red Shift...?

My physic is really bad I have to say

Tom
 

Offline DrPhil

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Re: Question of the Week - Old Version
« Reply #257 on: 12/02/2005 13:14:19 »
I agree with Ultima. Back in the olden days (early 1900s) the luminosity of Cepheids was used as a yardstick, unfortunately they are not bright enough to be seen beyond our local galaxies. Now, the apparent brightness of the Type Ia supernova is used to determine distances to galaxies billions of light-years from earth. Last year astronomers discovered a pattern in the energy emitted by gamma-ray bursts which they believe could help them map the most distant parts of the cosmos.
« Last Edit: 12/02/2005 13:15:31 by DrPhil »
 

Offline gsmollin

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Re: Question of the Week - Old Version
« Reply #258 on: 18/02/2005 16:52:05 »
quote:
Originally posted by NakedScientist

I'm sad that no one wants to have a go at this week's QOTW...:(



I was inattentive, since the "question of the week" never comes out weekly, so I missed this week's (month's?) QOTW...

Historically, the Cepheid variables were used as brightness standards to show that the stars in the galaxy in Andromeda were much further away than thought before the time of Edwin Hubble. I believe the Cepheids were calibrated using parallax methods, although I should be checking my history before I make that claim. Hubble was then able to calibrate the red shift of the spectrum in the Cepheids, and showed the correlation between that and the distance. He then applied the red-shift-distance correlation to very distant galaxies, and determined they were billions of light years away. Of course, the red-shift-distance correlation factor became known as Hubble's constant, and has been refined since that time.

Later: According to the history, the Cepheid variables are named after the star Delta Cephei, which were studied by Henrietta Leavitt. D. Cephei is close enough to use a parallax measurement for its distance. With that, plus a knowledge of the period-absolute magnitude relationship in the Cepheid variables, Leavitt used the Cepheid variables to measure the distance to the Small Magellanic Cloud.
« Last Edit: 22/02/2005 15:23:05 by gsmollin »
 

Offline simeonie

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Re: Question of the Week - Old Version
« Reply #259 on: 29/07/2005 12:51:29 »
if we had wings and a really strong chest could we fly?

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Offline ukmicky

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Re: Question of the Week - Old Version
« Reply #260 on: 29/07/2005 20:18:54 »
simeonie

I dont think so, human bones are to heavy and not flexible enough.
 

Offline neilep

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Re: Question of the Week - Old Version
« Reply #261 on: 29/07/2005 23:56:36 »
quote:
Originally posted by simeonie

if we had wings and a really strong chest could we fly?

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Well..I presume if we had a strong chest and wings we'd also have very strong other bits to compensate !!...and if we had feathers and a beak..we'd all be birdies too !!

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Offline Tronix

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Re: Question of the Week - Old Version
« Reply #262 on: 03/08/2005 20:32:58 »
im sure we could fly, but the wing span would be huge (remember the ptersaur?). Unless we had jet packs. come to think of it, we fly every day (and the wing span IS huge)...

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Offline spade23

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Re: Question of the Week - Old Version
« Reply #263 on: 20/08/2005 00:05:49 »
I think that that is a brilliant idea.:D:D:D


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Offline saanwal

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Re: Question of the Week - Old Version
« Reply #264 on: 21/08/2005 16:55:13 »
Dear Scientists
 
I want to know how much ozone layer is now left?
 
Please tell me.
 
Thanks

Saanwal.
 

Offline Razor

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Re: Question of the Week - Old Version
« Reply #265 on: 21/08/2005 18:46:26 »
quote:
Originally posted by saanwal

Dear Scientists
 
I want to know how much ozone layer is now left?
 
Please tell me.
 
Thanks

Saanwal.



Well im not sure "how much" ozone layer is left but this website should help you to answer your question:
http://www.nasa.gov/vision/earth/lookingatearth/25TOMSAGU.html


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Offline aasurfer33

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Re: Question of the Week - Old Version
« Reply #266 on: 24/09/2005 07:45:30 »
Hey really of the topic, but what does everyone on this post and the Dr. think the best college to go to for science in the states or anywhere else.
 

Offline pyromaster222

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Re: Question of the Week - Old Version
« Reply #267 on: 15/10/2005 20:22:30 »
the distance to other galaxies is measured by the dopler effect (or red shift) this is when galaxies move away from each other and is caused by light waves being "stretched" towards the red spectrum of light. Therefore the light has a reddish tint when observed. The severity of the red shift tells us how far away the galaxy is because the further a galaxy is from ours the faster its moving away, due to the fact that the universe is expanding in all directions at once.
 

Offline NakedScientist

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Re: Question of the Week - Old Version
« Reply #268 on: 04/11/2005 18:04:22 »
QOTW RETURNS !

To kick off a new series of "Question of The Week", have a go at this week's 'poser' :

- WHAT STOPS METAL BOATS (MADE OF IRON) FROM GOING RUSTY ?

Have a go below, answer next week.

TNS
 

Offline neilep

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Re: Question of the Week - Old Version
« Reply #269 on: 04/11/2005 18:15:59 »
Do they put a sign on it that says ' No Rust Allowed ' ?...because if I was a bit of rust that would stop me !...or is just some Anti-rust paint  ?

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Offline ukmicky

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Re: Question of the Week - Old Version
« Reply #270 on: 04/11/2005 23:46:52 »
Canít remember what their called or how exactly they work, but donít they place special metal blocks under the ship which when given a charge attract the electrons released by the interaction of the salt water on iron, causing the metal blocks to rust rather than the ship. Or something like that:)

Michael                                      
« Last Edit: 04/11/2005 23:48:11 by ukmicky »
 

Offline pyromaster222

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Re: Question of the Week - Old Version
« Reply #271 on: 12/11/2005 21:02:59 »
they have a magnesium or zinc block attatched to the boat. the magnesium or zinc is more reactive than iron and so is sacrificed and therefore reacts with the sea water rather than the iron. this means the iron stays rust free. this process is also used in galvinisation of fences etc. but the term galvinised is referred to objects covered in zinc..not any other metal.
 

Offline DrN

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Re: Question of the Week - Old Version
« Reply #272 on: 20/11/2005 22:56:36 »
ah yes - I remember something about a zinc (or somethng) block attached to the sewage pipe to stop that rusting. obviously it would be minor disaster (and not just to the blue flag status of the beach) if that got holes in it. so it must work I guess.
 

Offline chris

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Re: Question of the Week - Old Version
« Reply #273 on: 20/12/2005 08:57:19 »
ANSWER TO "WHAT STOPS METAL BOATS (MADE OF IRON) FROM GOING RUSTY ?"

You're right. Apart from a coat of paint, corrosion of the metallic parts of boats, pipes and oilrigs can be reduced by sacrificial protection. Put simply, by connecting a more reactive metal to a piece of iron - either by direct attachment, or even with cables, the more reactive metal sacrifices itself to prevent the iron from oxidising. This is analogous to a displacement reaction with electrons passing from the more reactive metal to the iron. Usually zinc (galvanising), or magnesium, are used and are referred to as "sacrificial anodes".

The chemical reaction is :

3Zn -> 3Zn++ + 6e-
2Fe+++ + 6e- -> 2Fe

In other words, the zinc (or magnesium) is oxidised (and dissolves) instead of the iron. The process will work as long as the two metals are electrically connected and in contact with the electrolyte. In the long run it's cheaper to replace the anode several times than to replace the boat !

Chris

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Re: Question of the Week - Old Version
« Reply #274 on: 20/12/2005 08:58:32 »
Here's this week's Festive Christmas QOTW to mull over whilst enjoying your mince pies and port :

"WHAT IS HEAVY WATER AND WHY IS IT USEFUL ?"

Merry Christmas.

Chris

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Re: Question of the Week - Old Version
« Reply #274 on: 20/12/2005 08:58:32 »

 

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