81

Physics, Astronomy & Cosmology / Re: Why Does Re-Entry Have To Be Fast ?

« on: 12/08/2005 15:45:51 »

quote:Originally posted by Allison

The fuel used to power the space shuttle is super-cooled liquid hydrogen, rather than some kind of petroleum-based fuel.  The hydrogen is mixed with liquid oxygen inside the engines (the reaction provides the energy required to blast off), and the clouds of "smoke" that appear when the shuttle blasts of is actually water vapor--incredibly dramatic water vapor, but much less harmful than exhaust from a tail pipe.

Unfortunately, this is only half the story. The three main engines are hydrogen-oxygen powered. The two boosters, that provide ~80% of the lift-off thrust utilize solid fuel. The oxidizer in the Shuttle solids is ammonium perchlorate, which forms 69.93 percent of the mixture. The fuel is a form of powdered aluminum (16 percent), with an iron oxidizer powder (0.07) as a catalyst. The binder that holds the mixture together is polybutadiene acrylic acid acrylonitrile (12.04 percent). In addition, the mixture contains an epoxy-curing agent (1.96 percent). The binder and epoxy also burn as fuel, adding thrust.

As you can see, there are many pollutants available from the SRBs. Once again, the decision to use SRBs was economic. Liquid propulsion was always first choice.

However, Boeing's new Delta IV rocket has an all cryogenic hydrogen-oxygen propulsion system.

"F = ma, E = mc^2, and you can't push a string."

82

Physics, Astronomy & Cosmology / Re: What is the first push of the universe?

« on: 12/08/2005 15:34:34 »

The origins of the idea rest with a Catholic priest from Belgium, Georges Lemaitre. He proposed the idea of a universe created at a single instant in the past, which he called, "a day without yesterday", and expanding outwards afterwards.

Henrietta Leavitt developed the cosmic yardstick using Cepheid variable stars. Subsequently, Edwin Hubble discovered that galaxies were rushing outwards, and the further away they were, the faster they receeded. Running the clock backwards gives the inescapable conclusion that there was a beginning.

Other scientists were opposed to this idea. Albert Einstein believed the universe was static when he formulated General Relativity (years before Hubble). However, GR does not admit to a stable solution: The universe must be either expanding or contracting. A. E. inserted another term into the equations, called the cosmological constant, that would allow a static solution. Unfortunately, the universe still is not stable. Pertubations from a static balance result in collapse or expansion. When Hubble showed the universe was expanding, Einstein called the constant, "my greatest blunder."

Other cosmologists believed the universe was eternal, and were openly hostile towards the idea of a beginning to the universe (despite the fact "In the beginning" is the first three words of the Bible). Fred Hoyle was one of them, and he skoffed at the new theory, calling it "this big bang idea". So it was named by a detractor.

Many people have had strong feelings about this. You can find detractors everywhere, but the truth will out. As more and better observations have become available, this is the only viable answer today. The exact form of the theory keeps changing, but this is what science is all about: Discovering the nature of nature.

"F = ma, E = mc^2, and you can't push a string."

83

Physics, Astronomy & Cosmology / Re: Does centrifugal force actually exist?

« on: 11/08/2005 16:11:47 »

The device I am referring to used a pulsed magnetic field to induce eddy currents in the body tissues. The currents were larger in the vicinity of a broken bone than in healthy tissue. The electric current flowing across the broken bone sped up the healing process. In geriatric patients, the results were rather impressive, with bones healing in a few weeks that had not healed in a few years.

"F = ma, E = mc^2, and you can't push a string."

84

Physics, Astronomy & Cosmology / Re: expanding universe

« on: 11/08/2005 11:03:17 »

quote:Originally posted by ukmicky

TO Gsmollin
I don’t doubt your knowledge and have always treated your replies as gospel.
It’s good to have a source you can trust.
But just out of interest have you ever supplied an incorrect answer on this forum.
Have you ever got anything wrong? Its human to err, have you erred yet.
Or are you inerrable.

OK, it's possible I am erring for the first time, on this forum, by responding to this post. I simply try to answer questions, and occasionally post one, for the fun of it. Some people post good questions, and I enjoy finding the answers. It is rare that I fire from the hip: Most of the time I have checked references before I answer. That may be why it seems that I am "always right", but in reality, it is only good research. Anybody can do it, who has an interest. Other times, like when the question is really difficult, I will simply suggest avenues of research to the poster. Other stuff I don't get involved, like all the "God" questions. It's not science or physics, and really belongs in "just chat".

If you prefer, I won't respond to your posts. I don't want to offend you.

"F = ma, E = mc^2, and you can't push a string."

85

Physics, Astronomy & Cosmology / Re: Does centrifugal force actually exist?

« on: 11/08/2005 10:49:54 »

What is the name of this company? I used to work for a company making magnetic healing aids. To be precise, they were electro-magnetic healing aids, not magnetic jewelry. I thought the work was promising, but the company went bankrupt after problems selling thir heart pacer. That aside, I always wondered if anybody else was working on EM healing devices.

"F = ma, E = mc^2, and you can't push a string."

86

Physics, Astronomy & Cosmology / Re: expanding universe

« on: 11/08/2005 02:20:34 »

quote:Originally posted by simeonie

Well not exactly expanding but more is becoming possible to view.

----------------------
Time is like a knife..... slowly and relentlesly.... cuts the cored of life.

-__- my website!!!!
http://www.simeonie.co.uk
has forums too!
Think about it! lolz

No, exactly expanding space. GR tells us that space can expand. Do some research on it. You don't have to believe it to make me happy, but that is exactly what it tells us.

That is different from the light-cone horizon, which just says that as time goes on, we can see further back in time because the light from distant events has had more time to reach us. So every year, we see a light year further away.

"F = ma, E = mc^2, and you can't push a string."

87

Physics, Astronomy & Cosmology / Re: Does centrifugal force actually exist?

« on: 11/08/2005 02:14:13 »

quote:Originally posted by Ultima

If there was only a force acting on the rock towards the centre it wouldn't stay in a circle, it would just accelerate inwards.

wOw the world spins?

Yo, Ultima, the rock IS accelerating inward. But since the acceleration vector is always in a direction perpendicular to the velocity vector, all it does is change the direction of the velocity vector from a straight line to uniform circular motion. Also, the work is zero. I'm gonna tell your physics teacher to bitch-slap you anyway.

"F = ma, E = mc^2, and you can't push a string."

88

Physics, Astronomy & Cosmology / Re: Does centrifugal force actually exist?

« on: 10/08/2005 21:01:40 »

quote:Originally posted by Bass

Since I study rocks and know just enough physics to be dangerous- I'm still trying to figure this out.  Is there a separate centripetal force?  It seems that in orbitting celestial bodies it is actually gravity, or the tension in a string when whirling a rock about your head, or the reaction force of the road against your tires as you squeal around a turn?
Is centrifugal force really a measure of the change in inertia?  When I whirl a rock around my head and let go, it travels at a tangent to it's circular motion (perpendicular to the radius at the point it is let go).  If centrifugal force actually exists, shouldn't it travel directly away from the center of rotation?

Prediction is difficult, especially the future.  -Niels Bohr

The centripetal force is the force accelerating the rock towards you, in the center who are whirling it about you. This force has a magnitude equal to the tension in the string, and a rotating direction that always points at you in the center. Centrifugal force is the reaction force that you feel on the other end of the string, which seems to be pulling the rock away from you. If you let go of the string, the rock flies off in a straight line, since the centripetal force is now zero.

89

Physics, Astronomy & Cosmology / Re: expanding universe

« on: 10/08/2005 20:54:08 »

quote:Originally posted by David Sparkman

Spectroscopy is one of my fields, though only from an engineering point of view. I am not sure what you mean by a red shift of 1000. The units are not familiar to me.

The quantium of energy for any element depends on the relationship between the electron and the nucelus of the atom. Temperature changes this relationship, moving at relativistic speeds does as well.

But gravitational compression in things approching neutron stars should also change the energy levels of the different shells. So I would not be so sure of the standard interpertation. There are still a lot of strange things we may not have seen or considered.

David

Clearly.

If you are familiar with spectroscopy, then you already know what a Dopler shift is. If a light souce is moving, its wavelength will be shortened or lengthened. Redshift is a dimensionless number that gives a ratio for the amount the wavelength has lengthened. A formula can be found here: http://www.astro.virginia.edu/~jh8h/glossary/redshift.htm

Cosmological redshift is much more difficult to understand than Dopler shift. General Relativity tells us that space is expanding between us and the rest of the universe, and is carrying away distant galaxies. A discussion of cosmological redshift can be found here: http://www.astronomycafe.net/anthol/expan.html

Google "cosmological redshift" for 201,199 more entries to read and ponder.

90

Physics, Astronomy & Cosmology / Re: The god particle

« on: 10/08/2005 20:30:35 »

It's actually the title of a book by Leon Lederman. You can review it here: http://www.amazon.com/exec/obidos/ASIN/0385312113/qid=1123701646/sr=2-1/ref=pd_bbs_b_ur_2_1/103-3935916-3025459

It has been said that amongst the genre of popular physics book, one loses half the readership for every formula in the book. It's also been said that one doubles the readership for every mention of "God" in the book. I have skimmed this book in a bookstore, but declined to read it because Lederman's style did not appeal to me. I think the use of "God" in the title is a cheesy gambit to grab readership. Other than that, there is nothing about the Higg's boson, or Higg's physics in general to suggest any connection with God.

91

Physics, Astronomy & Cosmology / Re: how does the fabric of space work

« on: 10/08/2005 20:19:02 »

Right on!

92

General Science / Re: What's the hottest temperature an object can reach

« on: 10/08/2005 20:15:47 »

quote:Originally posted by Razor

I believe there is no maximum temperature that nothing can exceed as long as there's something to be able to create it,the big bang could of been as much as 100,000,000,000,000,000,000,000,000,000,00...etc. as long as there was something to create that mass of heat

"Caution: Cape does not enable user to fly."
-Batman costume warning label

In classical physics, you are correct. However, because classical physics does not quantify energy, it actually predicts a sort of explosion of high temperature energy, which was called "the ultraviolet catastrophy". This problem motivated the first quantum mechanical explanation of electromagnetic radiation, and solved the blackbody radiation problem. QM makes many shocking predictions, and an upper limit to thermal energy is not the most shocking. There is also an upper limit to elementary mass, and a lower limit to space.

I think the warning label was originally on a Superman costume. Likely, all caped costumes carry that warning now.

93

Physics, Astronomy & Cosmology / Re: expanding universe

« on: 09/08/2005 22:03:06 »

quote:Originally posted by ukmicky

expanding universe

gsmollin

Could it be possible that something beyond our universe is pulling on and stretching it.
Rather than the universe and the fabric of space being expanded from something within

Something like that is one of the results of m-brane theory. It has to do with gravity, which is supposed to cross the universal boundaries. I am not in a position to answer any questions about it, though. That is is still for a specialist.

About recessional velocities: Many of the redshifts scientists measure on receding galaxies, and the cosmic microwave background radiation, are explainable by concluding that the receding galaxy has recessional velocity > c. I think any redshift greater than 3.2 is supposed to recede > c. The CMB has a redshift of ~1000. This does not square with SR. The explanation is that there are two kinds of velocity. One is in a local reference frame, where no material velocity exceeds c. Also, we still measure the speed of that redshifted CMB as c. The test is that "No thing can go past you at >c."

A recessional velocity never goes past you, and is not part of your local reference frame. It can exceed c, and this is explained as an "expanding space".

94

Physics, Astronomy & Cosmology / Re: how does the fabric of space work

« on: 09/08/2005 21:47:28 »

I bought some fabric of space, and my wife made some curtains out of it for my daughter[8D].

95

Physics, Astronomy & Cosmology / Re: Does centrifugal force actually exist?

« on: 09/08/2005 21:44:17 »

Yea, I jumped to the bottom here to say that, and found Ultima beat me. However, I don't think my old freshman physics teacher was the bitch-slappin' type...

What we call "uniform circular motion" in the Newtonian physics book applies an acceleration to a particle that always points to the center of the circle, and always orthogonal to the tangent velocity vector. The acceleration is central-seeking or centripetal. The acceleration is produced by a centripetal force, f=ma.

Centrifugal force is a reaction force that we feel as we are the object being accelerated towards the center of a circle, or radius, such as in a turn. We feel every part of our body being pressed towards the seat of the carnival ride, for instance. We then say we have felt the centrifugal force, but it is only a reaction to the centripetal force that is causing the acceleration.

96

General Science / Re: What's the hottest temperature an object can reach

« on: 09/08/2005 21:32:59 »

Nothing has ever been at 0 Kelvin, to observe if it disappears. However, there is no theoretical justification for this idea. Temperature is a measure of just one kind of energy. In atom or elementary particle still maintain their other forms of energy, without thermal. For instance, electric charge is still present in an atom, independent of its temperature. The rest mass is still there. The orbitals of an atom would remain without thermal energy. There may by other phases of matter below our present limits of refrigeration, with some surprising properties, however I have no reason to believe that invisibility is one of them.

97

Physics, Astronomy & Cosmology / Re: Why Does Re-Entry Have To Be Fast ?

« on: 09/08/2005 17:21:32 »

The moon and earth both orbit each other around their joint center of mass. This is the same for any other orbit, anywhere. The moon and earth are thought to have been formed from the same material, but separated from each other by a cosmic collision after formation. I suppose you could call that a sister planet.

The changing orbit is a result of the ocean tides. These cause the moon to orbit around a point slightly behind the earth's center of mass, and angular momentum is not conserved. The angular momentum of the earth is transfered to the moon, and its orbit rises. Earth's rotation is slowing. Interestingly, this process is very strong now, and apparently not so strong in the past, else the moon would be in a higher orbit. Apparently, the present continent arrangement gives a high tidal force, and the land mass was in supercontinent form for long periods in the past, which had low tidal force.

98

General Science / Re: What's the hottest temperature an object can reach

« on: 09/08/2005 17:08:15 »

Particles in a sample can't travel at light speed. However, they could travel arbitrarily close, at least in SR.

In QM, there is the Planck temperature, defined here: http://en.wikipedia.org/wiki/Planck_temperature
According to that, the hottest temperature is 1.4 x 10 ^32 Kelvins.

99

General Science / Re: Do fish really have a 3 second memory ?

« on: 09/08/2005 17:03:01 »

I think the 3 second memory bit is all mixed up with the 3 second association of memory. I also think people thought goldfish had no memory because they would keep eating until they got sick and died. Well, humans do the same thing.

100

General Science / Re: What is a Sonic Boom ?

« on: 09/08/2005 16:59:55 »

Any distubance, in air, water, or any other medium is transmitted through the medium at the speed of sound, in that medium. As an object moves through the medium, the medium is compressed by the passage of the object, and waves flow out in front of the object. You can see this in a boat moving slower than the speed of its bow wave. As the object reaches the speed of sound in the medium, the object catches up with the bow wave, and it becomes highly compressed. This is the shock wave. As the object exceeds the speed of sound, the supersonic shock wave forms on its leading edge, and spreads out to the sides.