1641

Geology, Palaeontology & Archaeology / Re: How sands from different places vary

« on: 05/04/2005 12:27:49 »

Think about:
 how much energy the collisions are going to have had, and how this will affect the shape and surface of the grains.
how long it is going to have been battered, and the affect on the shape of the grains and the minerals that are still sand sized.

1642

Physics, Astronomy & Cosmology / Re: Pulling String a Universe Wide ?

« on: 04/04/2005 17:40:41 »

However stiff you tried to make the pole the wave of movement could never move faster than the speed of light, this is because the electric forces between the atoms are passed on by photons, and these can not move faster than the speed of light, so the atoms must move considerably slower than this due to their inertia.

I think possibly the stiffest material we know of is diamond which has a speed of sound of about 12000m/s so you would be waiting a long time for the other end of the rope to move, even just across the solar system

1643

General Science / Re: Are Scientists Corruptible?

« on: 30/03/2005 19:01:41 »

Sorry to reveal my ignorance, but are NIH employees researchers, or the people who fund research? If they are researchers, unless there is a conflict of interest with their research, why would it be a problem?

If a researcher is researching in a similar field to a company and could be in a position to disprove the effacacy of one of their drugs for example there could be an issue, but why should there be a limit on a biotech researcher owning optoelectronic shares?

Possibly there should be some way of investigating insider dealing, or insider publishing, but this could be difficult.

If the NIH employee is dolling out research cash then you probably want to be more careful...

1644

Geology, Palaeontology & Archaeology / Re: Supervolcanos

« on: 30/03/2005 14:46:42 »

If I remember rightly from my first year Geology course, seismic activity can be indicative of imminent volcanic activity, as moving magma tends to stress and crack the surrounding rock, but really big quakes like this one are associated with plate boundaries, where you have massive lumps of rock grinding against each other under pressure, and are not directly associated with volcanos. The stresses produced by moving magma are just not big enough to produce this size of eathquake.

I suppose if a nearby volcano was about to go off a big earthquake could trigger it, but it would have gone off in the next couple of years anyway.

1645

Chemistry / Re: Demonstrations

« on: 29/03/2005 16:50:13 »

What do you mean by cooking?

If you have a fairly general interpretation:

You could do making butter from cream - you keep beating it and the droplets of fat get bigger and bigger as it gets stiffer and turns into whipped cream, and then very quickly they all join up and form an emulsion of water in fat (rather than the other way round in cream) and it forms butter.

You can apparently make an eggwhite  go white by adding liquid nitrogen, but that possibly doesn't count.

1646

Physics, Astronomy & Cosmology / Re: Feasibility of Hydrogen – Antihydrogen Power

« on: 26/03/2005 21:51:41 »

Last time I heard about this, they had made about 6 anti-hydrogen atoms, which lasted for a few micro seconds before they crashed into the end of the apparatus. I think it is hard to make, because you have to persuade the anti-protons and positrons to be going at approximately teh same speed, and as you tend to make these things by smashing particles together, so they are going pretty quick to start with.

according to:
http://ppd.fnal.gov/experiments/hbar/Pub-97-398-E.pdf

which is quite old, they make the anti-hydrogen in a anti-proton ring, and detect it by it's tendancy to fly out of the ring, and they then ionise it again to make sure that it consists of a positron and an anti-proton.

and
http://ppd.fnal.gov/experiments/hbar/Pub-97-426-E.pdf

would indicate that the anti-hydrogen is still moving at relativistic speeds.

so essentialy they don't contain it!

1647

Physics, Astronomy & Cosmology / Re: Which Metal Condenses On The Mountains Of Venus

« on: 26/03/2005 21:39:37 »

It is interesting, this has some nice pictures of the effect:
http://jules.unavco.org/Voyager/Docs/ImageGallery/venus_reflectivity

There are several metals that would evaporate gently at the 400 celcius on the surface and condense again at a lower temperature (lead for one - you are supposed to be careful about the vapour when you melt it), what confuses me is why they don't react with all the corrosive stuff in the atmosphere (SO2 H2SO4 etc) to form something that isn't reflective.

1648

General Science / Re: Are we still evolving?

« on: 24/03/2005 22:02:35 »

As, to a fairly close approximation, all children survive to adulthood, isn't the only selection pressure how many children people have?

 So isn't the major selection pressure at the moment an inability to use contraception properly, a tendancy to sleep around irresposibly, or possibly belonging to a religious sect that emphasises prolific breeding? I am not sure I like the long term implications of this, or any conceivable solution to them.

1649

Chemistry / Re: Sodium power is greater than oil power

« on: 24/03/2005 17:53:51 »

I was reading the Chemical History of the Candle by Micael Farady which is brilliant, and he makes the point that a fuel that produces a solid waste product is a right pain as it won't get out of the way in a civilzed way. So even if you sorted out the other problems your cylinder would just gum up with Sodium Oxide or Hydroxide or whatever. Oh and if you think that Lead in fuel was a problem I hate to think what the reation woudl be to sodium hydroxide fumes coming out of your exhaust pipe.

1650

Physics, Astronomy & Cosmology / Re: Aeroplanes

« on: 24/03/2005 17:44:35 »

Moses does have a point in that the weight of the plane must in some way be transferred to the ground eventually. Think about a helicopter to stay up it must be pushing air downwards, this is the downdraft you feel. This will push you downwards, but the weight is spread over such a large area that the force is not dangerous an eh101 has a rotor area of about 270m2 and it weighs about 14tonnes or about 50kg/m2 which is about 5mBar which will make your ear's pop but not crush you.

A plane will behave similarly - the maths would be more complex as you would have to take into account the speed of the aircraft, but basically planes are much bigger than they are heavy so the air pressure below them isn't very high, so they aren't going to crush you unless they actualyl hit you.

1651

Chemistry / Re: How reactive is Francium?

« on: 24/03/2005 13:32:11 »

I seem to remember talking to a chemist a few years ago who said that Francium was not as reactive as Cesium, because the electrons are starting to move so fast that relativity significantly alters the properties of the atom, so it stops following the pattern of the group.

According to http://www.hull.ac.uk/php/chsajb/heavy_ho/5dmetals.html a Francium atom is smaller than a Cesium one due to relativistic effects, so this may well be the case. Apparently it also explains why gold is so unreactive.

1652

Chemistry / Re: what colors block UV light?

« on: 24/03/2005 13:17:03 »

This may sound silly, but the colour that will block UV is the colour that will block UV light... eg purple is the colour that will block green light, and yellow is the colour that will block blue light... this doesn't help you much.

Depending on the dye things that block blue light will probably be even better at blocking UV light, so use yellow or red filters...

The other option would be to get some transparent suncream which is designed to just block UV and sandwich it between two layers of something transparent to stop it drying out. Or I think normal glass will block UVB quite well.

1653

Geology, Palaeontology & Archaeology / Re: Why water on Earth and not Venus?

« on: 24/03/2005 12:59:19 »

"That now makes sense. I did not realise that the day was the same length as the year. That is a bizarre scenario - I wonder how that came about - anyone know ?"

It is called tidal locking... because the moon is near the earth the part closest to us is being pulled harder than the part further away (inverse square law) this will tend to pull the moon into an ovoid shape and is the same reason we have tides on the earth. Now when it was formed the moon was spinning far faster than it is now, this bulge would always point towards the earth, so if you sat on the surface you would move up and down a couple of metres every revolution.

Now squashing a fair sized moon every day uses up a lot of energy, and it must come from somewhere,  and if you think about the direction of the forces (I really need a diagram) it will come from the rotation of the moon. So the rotation will slow down gently until it isn't moving (there are a couple of extra effects due to solidification that will acually stop it rotating).

In Jupiter's moons this can generate so much heat that even a small moon like Io has enough energy to have active volcanism on it's surface.

In a similar way the tides are slowing down the rotation of the earth, but much more slowly as the earth has more angular momentum, and the moon's gravity is weaker. It is however a noticible effect, and there are 200 million year old corals that lay down a layer of growth a day, that have 400 day rings a year.

  Dave

ps The tilt conundrum could be to do with the formation of the earth and moon, which was supposed to have been when something the size of mars hit the earth, throwing off lots of debris into orbit to form the moon. If it hit slightly off centre you could quite easily end up with a tilt.

The tilt does change a bit with time in one of the Milankovitch cycles (http://www.homepage.montana.edu/~geol445/hyperglac/time1/milankov.htm), but not very much 21-24.5 degrees.

1654

Physics, Astronomy & Cosmology / Re: Why does Helium make my voice pitch change ?

« on: 24/03/2005 12:23:00 »

I think the link Chris wanted was:
http://www.phys.unsw.edu.au/PHYSICS_!/SPEECH_HELIUM/speech.html

I think it basically says that your voice system consists of two parts your vocal chords/folds and your throat. It is a bit like a very short trombone, the vocal chords are like your lips in a trombone and the throat like the tube.

 The vocal chords vibrate produce lots of harmonics f,2f,3f etc. (where f is the lowest frequency you produce)  setting the base frequencies of the voice.
Your throat is a resonator, so it will vibrate better at some frequencies than others, so it will affect the  relative strength of each of the harmonics.
eg if you make your mouth longer when you are humming it will make the lower harmonics stronger and the higer ones weaker sounding deeper. The relative strength of these harmonics are called the timbre.

Because the speed of sound is much faster in helium it is like halving the length of your throat (but less painful). The high harmonics are strengthened and the low ones weakened, so your voice sounds higher, without actually changing the frequency of your vocal chords.

Dave

ps It also has the perculiar effect of giving me an ozzie accent... I am not sure why
 

1655

General Science / Re: Strange Hand Thing

« on: 24/03/2005 02:28:23 »

Isn't raising one eyebrow at a time a similar sort of skill - at one point I decided to learn to be able to do this, and I did it by standing in front of a mirror, and pressing buttons in my brain at random until one eybrow raised, then slowly just one eyebrow raised more and more, until I can now raise eyebrows at will.

 Is this because you have a sort of telephone exchange somewhere in your brain that takes commands from your concious brain -raise an eybrow- and translates them into 'contract muscle 145 40%, 184 35%, 243 80%...' and the defining of these commands is what children do a lot of for the first couple of years.

1656

Physics, Astronomy & Cosmology / Re: Feasibility of Hydrogen – Antihydrogen Power

« on: 24/03/2005 01:54:41 »

Unless we find a antimatter mine somewhere (a rather scary thought) antimatter will never be a source of energy, as you will always have to put in more energy (at the moment millions of times more) to make it than you would get out.

This said you can't beat antimatter for energy to weight ratio. According to Einstein E=mc2 is the best it is possible to get, so where this is important, like interstellar travel (you have to carry all your fuel with you) and yes building really unpleasent bombs, it would come into it's own. This is however a long way into the future.

PS if you wanted to store antimatter it would be a lot easier to do so as anti-protons and positrons rather than anti-hydrogen, as you can move them around with electric and magnetic fields - antihydrogen would tend to just drift to the edge of your jar... with unpleasent results.