Site Map

Get a Straight Answer

Please note!

This is just a selection--

either

or else

For an index file listing questions by topic, click here.

For a list including questions 28--324, click here.

396A Posssibility of Asteroid Hitting Earth (1)
396B Posssibility of Asteroid Hitting Earth (2)

452. What Book covers material of "Stargazers"?

Hello, Dr. Stern

Question: What bound book(s) will enable to obtain most if not all of the information in your online book "From Stargazers to Starships".

The reason that I want this information is I may be quizzed on it by a Reality TV show.

Reply

I hate to disappoint you, but no such book exists.

At one time I considered publishing one, but as the video screen is edging out printed paper, it is hard to get publishers interested . So I chose instead a "book on the web" which is getting fairly wide use, and has many advantages over the printed version--fast updating, instant availability at no cost, and so forth. For a 78-year-old retired physicist this may still be the best way of getting the word out.

Getting the information together is not hard: just copy onto your computer the "zip archive" http://www.phy6.org/stargaze.zip (13.4 Mb, and that includes 3 or 4 translations and all illustrations). That gives you a compressed file which automatically "decompresses" into all HTML files and folders of "Stargazers", except maybe very recent addition not yet on the web. By reading systematically through it all, you will have all the information contained in "Stargazers"

And aye, there's the rub. It is an enormous and diverse collection of material, gleaned over the years from many sources, and what adds difficulty is that, to make it more interesting, it is padded with an enormous number of trivia,. Where is the "Sundial bridge"? Who first estimated the distance of the Moon, and how? Who was the man with the golden nose? What day of the year was Dr. Robert Goddard's personal holiday? On what day of the year was George Washington Born? How do astronauts measure their mass in zero-gravity conditions? Who discovered the 11-year cycle of sunspots, and how? Who said and on what occasion "The Italian Navigator has just landed in the new world"?

One could fill the rest of the page with questions like these, and I know of no systematic way of locating the answers, short of reading through the entire collection. If you try doing that, you might never reach your final destination--but at least I hope you will enjoy the journey.

Good luck!

453. Climate Change

Dear Dr. Stern

The attached email, which I sent to some friends will seem to you very amateurish. I took my own advice therein and consulted a retired army meteorologist who teaches as an adjunct at a nearby University. He pointed out some glaring oversimplifications and errors. But on the other hand, he seemed biased toward denying that anything should be done about global warming.

My intuition, is that the stronger alternation of North-South currents in recent years which cause some of the public to say, "This winter's storms refute Global warming theories." are themselves a product of the added heat stored in the tropical and subtropical oceans, and that some bodies in the Arctic and subarctic which remain cold from previous centuries (I know better than to say, "stored up cold . . .") continue to absorb heat and so contribute to the intense and long lasting cold wave which brought snow to Houston and ice to Orlando.

So my meteorologist's first criticism was that I was ignoring the isolation of the Circum-Polar winds from even the sub-Arctic. and the major geographic sources of the "coldness" of recent fronts was in NW Canada or Eastern Siberia. When I searched Google for "Climate, winds", your website with the S-series of lessons came up first. I found it quite interesting, but not the direct answer to my questions.

My meteorologist and I both agreed that the situation is more complicated than I had pictured, so I asked if he could give an example of some analysis which would weigh the various factors involved to suggest whether my suspicion that the full impact of Global warming will be delayed somewhat until the polar sea ice and the icecaps in Greenland and Antarctica are sufficiently melted. Unfortunately, he couldn't..

Am I flatly wrong in my intuitive suspicion, or is there a person or source which I might consult for a more reasonably stated concept? I know you indicate that Physics is more your specialty than Meteorology, but perhaps you can suggest a book, person or website I might consult.

Thank you for any comments you can send.

(writer is retired from the faculty of Sociology and Anthropology)

Reply

I just received your message, and my first reaction was: wow!

Then, since you were from Tennessee, I idly checked whether you came from the same institution as William Ferrel. No! But close!

In brief: your ideas are very, very much on a convergent track with mine. I too have wondered about the effect of "greenhouse gases" in the atmosphere--how much of it drives vertical heat transport vs. how much goes into the horizontal transport. Your message--if I read it right--suggests that the horizontal effect may be enhanced much more than the vertical effect, and if so, it may very well drive cold winds from the arctic--the return flow from the heating-up of the polar regions. Something like that was suggested in fact in

http://www.phy6.org/stargaze/stargaze/StarFAQ23.htm#q426

Art Hobson

Dr. Mark Schoeberl

Rossby waves

sea currents

454. A classroom Demonstration

(from a teacher)

I like the idea of interactive lecture demonstrations. Having students make Predictions before showing the demonstration is a nice way of getting them involved. It makes them think and ask questions before the demo is even shown. I like this format for making them think and question..

A demonstration that I do for Newton's third law of motion does follow the format of making predictions. It involves a zip line, horizontally attached from one side of the room to the other. On the zip line I have attached a two liter bottle to a wooden block that is hanging from the zip line by two pulleys. The two liter bottle is horizontal to the floor and free to move across the room as it slides across the zip line. The bottle is filled with hair spray and then ignited and quickly launches across the room.

I then ask the question, what did the rocket push off of to get across the room. Most will say the wall. I then place the bottle in the middle of the room and ask the students what will happen to the rocket now. This usually leads to a good discussion and one that I would rewrite in the interactive lecture format.

Reply

There exist many interesting "predictive" demonstrations. For instance, letting two metal objects, sphere and cylinder, roll down an inclined plane. Will they arrive together, or will one get ahead--and if so, which one, and why?

Another simple demonstration is putting a strip of cloth along the top of a table (its end hanging down past its edge), and placing a block of wood or metal (experiment privately at first) on it, away from the edge.

If you pull the strip slowly, the static friction will keep the block in its place, until it reaches the edge and falls off. But what if you yank it quickly? Have the students try predict the result!

Most are likely to say, because of inertia, the block will stay in place while the strip will slide under it. Try it, and that is approximately what the class will see. Then ask: "does the block move AT ALL?" Well... we'll have to repeat the demonstration.

This time place some reference object on he table next to the block, but clear of the strip--say, a book. By comparing the position of the block to that of the book, the class will notice that the block DID move. Less so if you yank the cloth really rapidly, but always some motion occurs.. What gives?

The answer is, as strip is yanked, the block lags behind, because of inertia. A force of sliding friction exists, but it is not strong enough to give the block the same acceleration of that of the strip.

Now one of the properties of sliding friction is that it is approximately independent of velocity. Whether the strip is yanked moderately fast or at maximum speed, the force of friction, while the block is in contact with it, is about the same, What differs is the TIME T it lasts, which is the time needed for the strip to clear the block. That is much smaller when one yanks real fast. The momentum F transmitted to the block is thus P = F T (actually, an approximation to an integral--F is an average force). The force F of friction is about the same whether the strip is pulled quickly or only moderately so. However, T is smaller the faster you yank, and so is the momentum transferred to the block. Inertia plays a role--but it is not completely simple.

(Full disclosure: This demonstration follows exercise 33, p. 85, in Ira Freeman's translated and edited version of "Theoretical Physics" by Georg Joos, 2nd. Ed. 1951.)

455. Why doesn't the Solar System Collapse?

Dr. Stern,

I have a query thats' been bothering me for some time.

Under the premises that two bodies cannot possibly consume the same volume in space while possessing a force of gravity (or else they would collide into each other) and the fact that Earth does have this force of gravity, is it not feasible to conclude that the Sun and the Moon do not possess any force of gravity?

curious cat

Reply

Hey, kitty!

If Earth, Sun, planets and moons started at complete rest relative to each other, then yes, gravity would pull them together and they end up smashed into a single object--a slightly larger Sun.

However, each has its own orbital velocity, and that is what keeps them apart.

Be careful! See

here

456. A Diamond Core for Jupiter?

Hello,

I am reading Arthur C. Clarke's excellent book "2010: Odyssey Two". In the book, he describes the core of Jupiter as a giant diamond. I have searched around the internet and have essentially learned that scientists are not 100% sure about what the core of Jupiter contains (or if, in fact, there is a core). I haven't seen any evidence that the core does contain diamond, or is a diamond. However, I know that although Arthur C. Clarke's books are fictional, he makes sure he does everything he can to make them accurate scientifically.

Is there any chance that Jupiter's core could be this way?

Reply

One fact which Arthur Clarke may have used in his speculation is that the pressure at the center of Jupiter is greater than anywhere in the solar system (except for the Sun which is much too hot for any solid to exist). That is because of the enormous weight pressing down from all sides, the weight of the biggest planet in the system.

Diamonds can form at such enormous pressures--in fact, that is how industrial diamonds are manufactured. Whether Jupiter's core has the necessary concentration of carbon (and absence of other atoms which interfere) is rather questionable, but claims in science fiction need not be realistic, just possible.

One thing which the core of Jupiter may contain is metallic hydrogen. The hydrogen atom has one outer electron, like lithium, sodium, potassium and their chemical relatives. These are metals--though very reactive ones, you need keep them in a container of kerosene, out of touch with oxygen in the air. However, solid hydrogen is dominated by the H₂ molecule, which only breaks down under enormous pressure. Metallic hydrogen in Jupiter's core is expected to be a superconductor, able to carry the enormous currents needed to generate Jupiter's intense magnetic field (look up article in Scientific American on this). Only catch: Saturn, Uranus and Neptune are also magnetic (though much less), yet the pressure at their centers is less than the one calculated as necessary for metallic hydrogen.

457. Why no "artificial gravity" on the space station?

Hello David

Your page showed up when I googled a question.

Often I have been pondering, why the space station does not use the centrifugal force, to get rid of the problems with astronauts' weakening of their muscles when staying in space for longer periods of time. Or, at least why it's never presented as an option for future space missions to Mars.

The only logical explanation to me is: it does not work in space - but I find that very very hard to believe.

Hope I get an answer.

Reply

Dear David

Such an idea was included in the first proposal of a space station--I think due to Werner von Braun in 1952, used in the "Colliers" article on spaceflight, years before the first artificial satellite existed. It is also featured in the film "2001, a Space Odyssey."

Look up my file

http://www.phy6.org/stargaze/Srotfram.htm

http://antwrp.gsfc.nasa.gov/apod/ap960302.html

http://en.wikipedia.org/wiki/Gemini_11

http://www.phy6.org/stargaze/Sskylab.htm

458. Precession of the axis of Mars

I am very interested in the phenomena of 'precession' and what it may or may not tell us about the possibility of the Solar System being in motion about a companion body. Ref "The Binary Research Institute" web site - well worth a visit.

I have recently been reading many papers on the WWW relating to the measurement of the precession rate of the planet Mars - I am not sure of the real details, but essentially they monitor the Doppler shift in the frequency of a radio signal sent from the Earth and looped back to Earth through a static transmitter on Mars - the NASA Viking and Pathfinder missions and soon the 'now not roving' Rover Spirit. Prior experiments - with Viking and Pathfinder support a Mars precession rate of order 8 arc seconds of angle per Earth year of rotation. The guts of the experiment determined the direction of the spin axis of Mars in each case, and then simply inferred the rate per year as a function of the elapsed time between the two measurement, about 15 Earth years.

Now the present value for the Earth's precession rate is approximately 52 arc sec per year, (c.f.; 8 for Mars).

The BRI is advancing the theory that approx 50 of the observed 52 arc sec of "Earth precession" is due to the fact that the whole Solar System has moved in a elliptical orbit by an amount equal to about 50 arc sec and only some 2 arc sec per year is due to the "pure" precession of the Earths axis.

Surely if the above were true and as both Earth and Mars are within the same moving reference frame - the solar system, then any measured precession of Mars would be its "pure" axial only precession.

I do not know enough about the experiments to know if this is the case, do you ? _If the experiments assume an Earth precession value of 52 arc sec per year as opposed to 2 say, then they may well be being misled about their understandings of the internal construction of Mars.
Can you help my lack of understanding here ?

Warmest Regards

Reply

Dear Andrew

I do not know the cause of the 8" precession of Mars
(http://en.wikipedia.org/wiki/Timekeeping_on_Mars)
The Earth's precession is much larger and is mainly caused by the Moon's pull on Earth's equatorial bulge caused by its rotation: it has been calculated (I wrote a program for it, too) and agrees with observations. With Mars, precession may be due to the Sun's pull on an equatorial bulge too (the small moons of Mars do not create much gravity). I am surprised to see it is as large as 8" per year!

459. Does the axis of the Sun precess?

Mr. Stern,

I was wondering, Does the axis of the Sun precess like the Earth's?

Reply

The Earth precesses because its equatorial bulge is pulled by the Moon and Sun. The Sun does have an equatorial bulge which is pulled by the planets, so in principle it should precess, but the force is small and the precession ought to be very very slow. Anyway, I don't think we can determine the axis of the Sun very accurately.

460. Can a microwave oven produce 900 deg Celsius?

hi
sir i have a two questions please answer
(1) a microwave oven can produce a temperature of 300C. Can we produce a temperature of 900C inside it? If yes what is the condition for it?
(2) A gas has two energy states "0" and "E" what is the internal energy of the gas.

Reply

A microwave oven typically produces 1000w of microwave energy, which can be absorbed by whatever is in it. So if you put a ceramic plate in it and a penny inside it, in principle the penny can heat to a high temperature.

But DON'T TRY DOING IT! All sorts of things can happen. The copper cover of the penny (inside it's zinc) may exclude the energy from inside the coin, high voltage may build up and sparks jump, or something can happen to the magnetron producing the microwaves--the energy may be dissipated in it and ruin it.

Or else, the oven has a circuit breaker protecting it (e.g. from destroying itself if it is turned on while empty) and it will stop working. It may or may not work again later.

Or the penny may glow red-hot, until the heat radiated (red and infra-red) equals the energy put in. It will act like a space heater. I don't know at what temperature, but the zinc will melt before it reaches 900C, I think..

Or else you may overload a circuitry and start a fire. Dry food or cardboard inside a microwave can be set on fire, but the circuitry may also be vulnerable.

Anyway, don't try it. Your second question is unclear. Energy states apply to ATOMS, and their difference is measured in electron volts. The excited state E generally lasts less than a millionth of a second and is then radiated away as a photon of light. . The internal energy of the gas depends mainly on its amount and its temperature.

461. Beaming energy through space

I am a student in electrical engineering (btech) and was wondering about efficiency of energy transfer through magnetically coupled resonance. Can you shed some light on that and can it be safe way without effecting objects surrounding the system?

Reply

The answer depends on what you mean by "energy transfer through magnetically coupled resonance." Energy is transferred in electric transformers by coupled magnetic flux, in a carefully designed magnetic circuit, and the high efficiency of this transfer is evidenced by the fact that even on a large scale, very little energy is lost to heating of the oil filling open spaces inside the transformer.

To transfer energy through air or space in a resonant way (and for large distances) you need a focused electromagnetic wave. Again, one can transform energy efficiently into such waves, as done in microwave ovens in the kitchen. However, focusing the beam over large distances and preventing it from spreading is difficult, and even if you capture it, it is hard to extract energy in a form other than heat, whose efficient conversion to other forms of energy is restricted by thermodynamics.

462. The year 2012

Dr Stern -
As one who works with Emergency Response teams, we are constantly exploring avenues for preparedness. Recently, the topic came up that the earth's magnetic field could be subject to an anomaly, as a result of the aligning of the planets, something that occurs every 26,000 years. Might this anomaly increase the EMF, thus impact electronic equipment (computers, digital communications, etc.)?

Reply

What you heard is probably best described as a modern urban superstition. What does happen in December 2012 is that the ancient Maya calendar ends its long cycle (12th or 13th, not sure), and some people identify this as the end of the world as we know it.

There exists no hard scientific support. The planets will not line up: see

http://www.phy6.org/stargaze/StarFAQ16.htm#q264

http://www.phy6.org/stargaze/Sprecess.htm

http://www.phy6.org/stargaze/Scalend.htm

reversed north-south polarity

463. The Earth's Precession Cycle

Dr. David Stern re. your article on Precession
Can you advise the time period of Precession Cycle with respect to Obliquity, or suggest where I might find such data?

How does the approximately 41,000 year cyclic change in Earth's obliquity (ostensibly between 22.1 -- 24.5 degrees) effect the time period of the Precession cycle? Does the Precession cycle slow when the tilt is at the maximum (24.5 degrees)? If the present Obliquity of 23.44 degrees produces a Precession cycle period of 25,772 years, what was the Precession cycle period when the Obliquity was 24.5 degrees? What will it be when the Obliquity is 22.1 degrees?

Thank you for any assistance you might be able to provide.

Reply

Dear Mike:

Short answer: I don't know. Milankovich linked ice ages to the celestial mechanics of the Earth's motion, and while the precession of the Earth's axis determines when in the northern or southern year the Earth-Sun distance is largest or smallest, the ratio largest/smallest depends on eccentricity, which has its own cycle. As you pointed out, there is also a fluctuation of obliquity, though the mean Sun-Earth distance does not change.

The only way to untangle all these is to simulate the Earth's motion over the last few million years, taking into account all known factors. I know that astronomers have done this, and some articles are referenced at the end of the section on Precession. And then there exist actually observed periodicities, from isotope composition of deep cores in the ice-caps of Greenland and Antarctica: from what I have read, they do not always agree with predicted ones.

The section on "Precession" is just a general introduction. This is not my field (although I have calculated orbital perturbations on satellites)--you will have to go to the experts, whose answers may require more technical know-how, or else may end in "we are really not sure about the details."

464. The empty space inside an atom

Dear Dr David P. Stern,
Kindly, what do we find inside atom between nucleus and outside electron?

Reply

Dear Carlo

Between the nuclei and the electrons we find space, of course, but it is not so simple. You write as if the nucleus and the outside electron had well established positions, and they do not. By the laws of quantum physics, those positions are uncertain, especially that of the electron. We might perhaps identify the position of the nucleus with that of the center of mass of the atom ("center of gravity" in common language), but about the electron one can only calculate a probability of it being found at some point in space. Mathematically that probability is represented by a wave, and as you probably know, a wave does not have a location but is spread out through space. In many ways the electron is then analogous to a light wave, described in
http://www.phy6.org/stargaze/Sun5wave.htm

The uncertainty in location is built into the laws of nature on the atomic scale, and to make it worse, if somehow you locate the electron, the act of locating (say by hitting it with another electron) leaves its new position uncertain again.

It is a rather mathematical topic, but I tried to explain some of it in general terms in
http://www.phy6.org/stargaze/Q1.htm
and in the 7 sections which follow it (Q2 .... Q8).

Go to main list of questions

(by topic)

Back to the Master List

Author and Curator: Dr. David P. Stern
Mail to Dr.Stern: stargaze("at" symbol)phy6.org .

Last updated 11-21-2008 Edited 2 November 2016