Fred's Science FAQ!

Welcome to the Ask Fred Project Page

Here you will find past questions and answers that have come through the office of Fred's World of Science. You can ask me anything science or math related, and I will try and e-mail you an answer in a few days and post it here. Many of the questions are humorous, and the answers are sometimes funny, but always entertaining, so you may get a kick out of the postings. -Fred

To post a question, Email Fred!

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Cyclotrons & Accelerators

From Tue Aug 18 15:24:30 1998
Date: Thu, 30 Jul 1998 11:26:16 -0500 (CDT)
From: "Fred, Bethany's Guy!"
To: Jim Flanagan
Subject: Re: Good Day

> Fred,
> My name is James Flanagan, from Houston. I saw the news program (I
> beleive CNN) several months ago, and have been looking for you since
> then. Your dad gave me your http address. Glad to finally contact you.
What news program is this?
I didn't know I was on CNN at any point

> I am not formally involved in the sciences, at least not for a few
> years. But I do have a very kean interest in science, and was very
> interested in the news show and what you are doing. I have some interest
> in the so called Zero Point Energy, as well as water at the molecular
> level, and would like to discuss some of these ideas with you.
Sure. I'd be happy to try and answer any questions you have
> Please let me know if you would be interested in corresponding on some
> of these interests. My email address is "".
> I am currently on my way from Houston to Nova Scotia, and will be up
> there for a few months. You can however email me at any time.
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Date: Sat, 14 Oct 2000 23:25:54 -0600
From: Daniel Lockhart
Subject: A Linear Accelerator

Hi Fred:

Great website and very interesting content!

I've got a quick question though -- I'm very familiar to Tesla coils, and
when reading about linear particle accelerators it occured to me that a
bipolar Tesla coil (two secondaries and primaries driven by the same tank
circuit with opposite phased outputs) would be a great power source for a
simple liner accelerator. Do you have any thoughts on this?

Seems like it would be an intriging project.

Daniel Lockhart

My answer:

Date: Mon, 16 Oct 2000 12:49:10 -0400 (EDT)
Subject: Re: A Linear Accelerator

Well- in answer to your question, you need to examine what a linear
accelerator is supposed to do in order to determine what power source is

While is is true that the bipolar tesla coil provides a great potential
difference through which you could accelerate particles, there is still
the problem that the Tesla coil produces alternating current. So while,
for example, an electron might be accelerated from left to right in a
simple accelerator when the positive side of the AC cycle was applied
on the left electrode and the negative on the right electrode. However,
in 1/(resonant frequency of the system) seconds, the polarity of the
electrodes will be reversed, and the electrons will be jerked back in the
opposite direction, with the same (but opposite directed) force.

+ ====== -
turns into
- ====== +

and the net accelerating force is zero

Now, if you were to take advantage of only the positive accelerating
cycle, and made the tube the right length, you could have the electrons
escape the tube before the cycle flipped, you would have a decent machine.
However, this is no different from a single stage, single electrode RF
linac (which is not particularly useful, and ridiculously inefficient).
Plus, when operating in this resonant mode, it is no more efficient to run
a bipolar tesla coil than it is to run a single more powerful Tesla coil.
The problem of an electron source sitting at the terminal of a Tesla coil
is a logistical nightmare. It would be much more feasible to have a
grounded electron source, and the Tesla secondary be the accelerating

So if an electron started off at one end of the tube, it would be jerked
around near the end of the accelerating tube, but the net acceleration
would be zero if the tube was not the correct length. However, if you
started off with electrons in the middle of the tube, you might be able to
get some electrons to accelerate out of the structure at both ends only
during the positive cycle of the AC current, sortof a dual-resonant
electron gun. But this is a really poor usage of the power of the tesla
coil again.

In the very early days of linear accelerator research, alternate forms of
high voltage generation were explored. One team of researchers used a
cable stretched between two peaks in the Swiss Alps. The cable was
roughly 2 kilometers long, and during stormy weather, the cable would
reach potentials grater than 15 million volts. An evacuated tube was
constructed to connect between the cable and ground, and ions and
electrons were accelerated. However, each time the experiment was
attempted, lightning would strike the cable, and the vacuum chamber would
explode rather violently. After two men died working on the project, it
was abandoned and the cable removed. At some point Tesla coil operated
linear accelerators were investigated, but it was before Wilderoe came up
with the idea of resonant acceleration. So, I imagine that it has never
really been attempted in a meaningful way.

Resonant acceleration techniques are typically very picky about the
stability of the oscillation in the driving voltage. Tesla coils are
notoriously unstable oscillators. As the caps heat up, the frequency
shifts. As the spark gap heats up, the duty factor wanders all over the
place. While the coil may be tuned up at a given time with no electron
beam, the addition of the electron beam will significantly change the
inductance and the capacitance of the secondary. A large mismatch can be
developed very quickly. This is an effect called beam loading. The Q of
the Tesla secondary wil also really change, and to be honest, I don't
exactly know what would happen. Since resonant acceleration requires such
stable oscillation, people use high power amplifiers and stable signal
sources for this type of application. Typically, large klystrons or
magnetrons are used to supply the RF power necessary for acceleration.

You can calculate how long an acceleration tube would have to be for a
given voltage developed by the coil, its frequency and the resultant
accelerating force that would be generated. My guess is that for a
typical tesla coil, the proper length tube would be far too long for
anything practical. The electrons would get to the end of the tube before
the coil reached its maximum potential. You may find that this approach
would not work for any set of parameters that would conveniently fit in
your garage.

I wish you luck. Don't let my entirely pessimistic ramblings discourage
you from playing around with the idea, though. I have thought a lot about
this stuff, so you emailed the right person, I think. However, if you
come up with something really cool, keep me informed.

Hope this answers your question.


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Justin's letter

So our bathroom sink doesn't drain as fast as it used to and I went to Target and bought a big thing of draino. I figured since I have so much left over, that I should take the remaining 2/5 of the container and dump it down the toilet. But all of the containers specifically say, "don't use in toilet." I think this might have just degenerated into a "the hell if I'm going to let the man tell me what I can do", but after last fall (when I used dish soap in the dish washer, and yes, it did fill the kitchen with foam) I thought I should pause and get your opinion. What do you think the problem is? They both drain to the same place. I'm thinking it's either that toilet drains use aluminum pipe fittings (or something else not found with sink drains that is reactive) or that they're worried that it might react with standard toilet bowl cleaners.


Well, there are really two problems here. First, the toilet has a porcelain gooseneck-shaped P trap that holds "stuff" in it for a while. The drano can actually etch and dissolve the surface. However, this pales in comparison to the real problem. The wax used to seal the toilet to the floor will react with the strong base of the drano, making it water-soluble via the miracle of saponification. That's right, it will actually turn to soap, just like lye and fat. This is why drano works in the first place, actually. Anyway- the toilet will eventually start leaking on the exit-side. Do not use in the toilet.
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From: Jeff Plato
To: "''"
Subject: Homemade strings instrument


I'm working on a class project with my grade 4 son and can't find a simple
formula to calculate the length of strings needed on his homemade instrument
to get some basic notes. I know that a C has a fundamental frequency of 131
hz, and that I can calculate the length for the standing wave using :
frequency = (v) / 2*L, where L is length and v is velocity (speed) of the

But here I'm stumped. Please help!

Jeff Plato

I replied:

Ok. Here we go; crash course in Physics 101:

Waves on a string:
To set up a fundamental oscillation in a string at 131Hz (by the way,
A above middle C is 440Hz), you need the following condition on the string (frozen
in time):

(the ascii art worked better in the email than on the web...)
The formula you gave me was correct, i.e.
f = v / 2L
where f is the frequency, v is the velocity of the wave in the medium, and
2L is twice the length. Now, you ask, what the heck is the velocity of
the wave in the medium? Sound (and vibrations in general) have different
speeds in different mediums. The velocity of sound in air, for example,
is 330 meters/second. The speed of sound in water is about 1000
meters/second. So, likewise we have to figure out the velocity of the
wave in the string.

The velocity is given by the following equation:
v = (F/mu)^(1/2)
or, velocity equals the square root of force divided by the mass density
of the string. Force is generally the tension in the string (in Newtons)
and mu is the mass per unit length (kilograms per meter) of the string.
Since it is not easy to figure out the tension, I suggest you "tune" your
instrument to a piano by tightening the string until the frequency of the
instrument equals the frequency of a given note on the piano. Using that

"calibration" you can calculate the v for the string. Then, you can vary
the length of the string to make different notes, as long as each string
is equally tight. You can check this with a piano again.

Does this sound like a fun project?
I think so.

I suggest the following book:

Tipler, P. "College Physics," Worth Publishers, 1987.
ISBN: 0-87901-268-4

This book is in wide use at colleges around the nation. It shouldn't be a
problem to find a copy at your local public library, or university.
Physics departments are typically very helpful in this kind of situation.

I used the following pages from Tipler:
Speed of waves, Chapter 16 p.378-381
Standing waves, Chapter 17 p.409-411, especially p.410

Good luck, and let me know how it goes, and what you decide to do!

*Here's the reply from Jeff*
Hey Fred.

Thanks for your help. A quick update and thanks:

It got very hectic near the end of the project. Your assistance got me
going and I had hoped to use the information to educate my son on how the
physics would work for the harmonics. Unfortunately, we didn't get a
to incorporate much of it in the written portion of the assignment. We
completed the instrument ( a Zither of sorts) and the report the evening
before it was due. - He got a 40 out of possible 40 marks. (only 10
marks were for the instrument that I actually did most of the work on, the other
30 was on presentation, content and accuracy).

Signed - a very proud Dad.


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Here's the most recent posting
This was from a 2nd grade classroom in Melbourne
Subject: Re: How Do You Determine The Weather
> Dear, Fred's Science
> How do you determine the weather do you
> just take a guess or just look at the past last years and how it was then?
> How would you stop the green house effect?
> By Mark C.
Dear Mark,
That's a great question. I wondered about that for a long time
myself. I finally asked someone who works for a National Laboratory who
studies weather patterns. What they do is they have giant computers that
calculate what the weather will probably do in the next few days based on
patterns and trends in the past. These computers are fed information from
stations all over the country such as the temperature, wind speed,
humidity, etc. The computer then takes all these numbers and facts, and
makes a model "earth." Using the model, the computer makes calculations
on where the big clouds will go in the next day, or where tropical storms
will turn, or any other weather phenomenon. The computers can usually
tell when it will rain 9 times out of 10.
Now we've all seen days when the weather man says that it will
rain, and it doesn't. We've also seen days when it rains and the weather
man says it won't. This is because no matter how powerful the computer,
mother nature is always unpredictable.
I hope this answers your question.
Have a great day
Fred Niell
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On Sat, 23 May 1998, Lorraine Liss wrote:
> Hey fred,
> I'm from canada and thinking of doing a science project on waves. Any
> Ideas or info on waves that you can send. You can email me at
> ""
I suggest you look in a college physics book about wave mechanics.
Probably the best type of projects involving waves are about standing
waves in 1, 2, and 3 dimensions. Look into it, and the more you read, the
more you'll think of.
Have fun!
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Subject: Help on Science Project!!!!
Hi Fred:
Not sure if you can help or not but here goes...
My wonderful 7th grade son chose to do a science fair project on
bicycle shocks (or suspension, I guess).
He's very interested in bikes, that's why he chose the topic.
Unfortunately, he's not sure where to start. Like should he compare
different types of shocks or suspension and if so how would he test
that. What kinds of things would he investigate relative to these
How to turn this into a science project?? That's the questions.
Any help would be greatly appreciated.
Regards - Donna

I replied:

Subject: Re: Help on Science Project!!!!
Hey! I hope I can help
The seventh grade science project is meant to teach kids how to think
about things around them in an analytical way. Obviously, no
groundbreaking research is expected in a science fair project; it is the
scientific process that counts.
The project should have a definite concept or problem that he must
investigate. Once the problem is fully understood, an experiment is
designed. Then, the results of the data are analyzed, and a conclusion is
In your son's case, a good project might be something like "Which
bicycle shocks work best?" Then he might go about testing the operation
of various shocks in an innovative, novel, or inventive manner. Based on
the results of the tests, he would conclude which shocks work best, and
briefly explain why.
To do the experiment, he would need to do a few things. First, he
would need to decide which shocks to test. Then, he would need to define
what makes a good set of shocks, and what makes a bad one. Based on this
distinction, he would design an experiment to test for the quality that
makes the bicycle shocks good. For example, he may see how much oil and
water mix up in a jar riding over the same terrain with different shocks.
That would in effect measure vibration qualitatively (lots of vibration =
lots of mixing = bad shocks).
I hope that this helps some.
Fred Niell

She sent me a note back:
Subject: THANK YOU!
Just a quick thanks to all of you for your help with my son's science
project about how bicycle shocks works.
His project was a big success and he learned a lot. Thanks for your creative
and innovative ideas and solutions. We couldn't have done it without you!

Donna Milo
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Subject: Re: Fan blade color oscillation

> A lady at work noticed that her white fan blades oscillate from blue to
> yellow when the fan is running. I've been trying to figure out why for her.
> I think maybe it's an optical illusion due to your eye's/brain's processing
> rate of the moving blade -- somewhat like the wagon wheel moving backward
> effect. That's just an initial guess for now. Any help you could give would
> be much appreciated.
The reason she sees blue and yellow alternately is because you have
flourescent lighting in your office. Flourescent lights actually flicker
at 120 times per second. This is far too fast for your eyes to detect.
But, have you ever noticed what happens when you watch something moving
fast in a strobe light? The image you see is the object frozen at
instants, and that is all your eye detects. It is as if the object is
only there when the light flashes. Well, flourescent lights act as a
strobe light that is going extremely quickly. In fact, they flash
alternately different colors. This may seem strange, but here's why. The
bulb is full of mercury vapor, and when the AC current goes (+), the
mercury vapor creates a plasma that is bright blue. Then the AC current
falls to zero. The plasma disappears, and the residual light is yellow,
caused by the phosphorous on the inside of the bulb still glowing. Then
the AC current goes (-) and the plasma is created again. This all happens
within 1/120th of a second. It goes through two flashes in 1/60th of a
second (our AC current is 60 cycles/sec). So, the lighting acts like a
strobe, flashing blue then yellow, and the fan is a moving object. So, I
imagine that she sees the fan blades alternating color from blue to yellow
as her eye just catches the fan blade going by while the light flickers.

I hope this helps some.

I got a reply:
Your answer is a lot of help. I eventually would have gotten close, but the
details you gave about exact fluorescent light operation was terrific. Thank
you so very much. It's nice to know there are other people other interested
in the weird little scientific quirks of the world just like me.


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On Wed, 3 Sep 1997, Kevin Davis wrote:
Hi Fred; The strangest thing happened today. I was clearing up and old
woodpile of trees that had been sitting for quite some time [ a year or
better ] and I put the large log sections in a giant woodpile. When I came
home later this evening the logs were glowing. The ends of the logs were
actually glowing in the dark! sort of the color of a firefly glow. Do you
think that this wood is polluted with some sort of chemicals or
radioactivity or could some kind of a phosphate-type compound have formed
over a period of time? This woodpile is scaring me !
....................Thanks.........Kevin Davis

Have you ever walked along the beach about dusk, and looked at your
footprints behind you? Many times, you will see an eerie, blueish green
glow in the depression of your foot in the wet sand. This is a type of
phosphorescence. Certain species of phosphorescent bacteria live in the
sand, just under the surface. Upon stimulus (your footstep), they glow.
Many species of bacteria exhibit this form of phosphorescence. What I
suspect is that your trees have leeched sap from the ends of the logs for
a year now as they dry up and rot. Sap is a wonderful growth medium -
high in sugars, low in inhibitory substances. What has probably happened
is that your trees have become host to some form of phosphorescent bacterium.
The bacteria feed on the sap, and one of their biproducts is
light. It would be interesting to try and isloate the bacterium, and grow
it in the lab. It is possible that you have found a new bacteria species.
On the other hand, since I have never heard of this kind of thing happening
on a wood pile before, it is possible (though incredibly unlikely) that there
is some form of chemical contamination. Good luck. Contact a local biology teacher,
and ask him/her if he/she would like to come out, and try and identify the critter.

Update Jeff Reese has this to add:
I noticed on your Ask Fred section someone asked about glowing wood in his woodpile. The glowing is caused by bioluminescence in the fungi Armillaria Mellea (Honey Mushroom) (or a related fungi). The fully grown mushroom does not glow but the mycelium and rhizomorphs do. This 'glowing wood' is usually referred to as "foxfire" and is most common in the cool nights of autumn.

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Sometimes I get hate mail :(
i have a few words that describe you by the way: whipped by your girl; overly boastful about your accomplishments; and if i had 1000 dollars, i could build a betatron that could blow all your accelerators out of the sky(by the way the 1000 dollars is for the photomultiplier tube, although i could probably build one for much less) thanx---------brought to you by the letter R-r-r-r
John F Morasco

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Some of the posts are pretty funny...
Subject: science, the ineffable
Magnet, n.: Something acted upon by magnetism
Magnetism, n.: Something acting upon a magnet.
The two definition immediately foregoing are condensed from the works
of one thousand eminent scientists, who have illuminated the subject
with a great white light, to the inexpressible advancement of human
-- Ambrose Bierce, "The Devil's Dictionary"
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I'm not even sure what this is...

Subject: Can anyone help this gentlemen?

Dear Dr.,

We are interested in the investigation of an physical problem, reduced
in website

Not to occupy its time, we include some phrase here.

<< Introduction to an elementary quantum model structure, easy and
accessible to all the readers. Provided with a centre of general symmetry,
expression of levels, resonances, perpendicular polarisations, and a
decisive value of effective section. With concrete dimensions, it allows to
register positions and displacements. Its adaptation to the Solar System,
makes the satisfactory position predictable of planets and the inverse
rotation of Venus and Pluto. It changes the inexact law of Titius-Bode for
distances among planets, in applied exact law between its lines. Also, it
completes other conditions made as the tests of physical confirmation.

It highlights a manifestation of geometric nature, of great beauty, until
now never view: The structure repeats inside if same with successively
smaller and perpendicular dimension.>>

We considered that it would solve what it seems an enigma of quantum
structure. We would thank any suggestion that helps its investigation.

Please. It does not have to believe to us. We requested to verify it.

If it is not of its interest, we requested pardon.

Thank you for their attention

Cyprien Olivert Crespo

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One great question
Subject: Science question
Hi Fred,
This is something I have wondered about for many years, and so far,
nobody has given me a satisfactory answer. There are zillions of cars on
our nations highways (not to mention trucks, busses, and motorcycles).
These vehicles have between 2 to 18 tires on them constantly wearing out
due to highway abrasion. Where does all that rubber go? I would think we
would see mountains of rubber dust everywhere, but we don't. Does it
simply disappear? What do you think?
Mike Gray
Amery, WI

I replied:
Subject: Re: Science question

Actually, the tire do rub thin, and the rubber does deposit on the roads.
But, the rubber bits are so small, that they act like dust. The black
streaks on concrete highways are deposited rubber. Each skid mark on the
road is some amount of rubber that has been rubbed off the tire. All that
rubber washes off the roads in the rain, and becomes a part of the soil.
It also becomes a part of the air pollution in the form of dust.
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Most of the emails, however, are about people interested in sharing research ideas...
Subject: cyclotron design question...

Dear Fred,
Hello. My name is Scott Rice and I am a freshman at Michigan State
University. Your construction of a working cyclotron absolutely amazes me.
Anyway, I am writing to ask you haw you generated a strong enough magnetic
field to contain the particles. In high school, I too tried to build a
cyclotron, but simply could not generate a strong enough magnetic field. (I was
trying to build a 1.5 MeV machine for hydrogen ions.) My magnets consisted
of two 9" cookie tins filled with steel shavings, with lots of wire wrapped
around the tins. (Without knowing the magnetic permeability, all I could do
was test the field I generated, and it was REALLY low for what I needed.) I
later thought of using iron lifting weights (from a dumbbell that weight
lifters use) for the magnet core. I have not yet had time to do enough
research into their composition to determine their effectiveness, but I
intend to when I resume my cyclotron building activities in the future.
Scott Rice

I work at the National Superconducting Cyclotron Laboratory on campus, and if
you are curious about its operation or how we do something, I would be happy
to answer any questions. (Just in case you wanted to know... :) )--
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Sometimes I get general science questions:
Dear Fred,
My name is Josh Boyden and I am a student at Galena High School in Reno
Nevada. In my chemistry class we are studying nuclear chemistry, and I am
doing a report on cyclotrons. I was wondering if I could ask you a few
questions about the cyclotron you made? If you would take the time to
respond to the questions me and my class will greatly appreciate it.
How many hours did you spend building your cyclotron?
Why do you feel cyclotrons are an important tool for studying nuclear
Do you think that particle accelerators and cyclotrons could be used to
benefit society?
What are some negatives of cyclotrons in your opinion?
What are some of the positives?
If there is one thing you could say to America's youth to make them more
interested in nuclear chemistry or nuclear physics what would it be?
Thank you very much for you time and have a good day.
Joshua Boyden
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Sometimes I get people who have worked on other accelerators...
Subject: Fred's Science Page
Very nice work.
I had worked at U of C on their Synchrocyclotron (450 MEV) in the Fermi
Lab. Accelerator building (unfortunately they trashed it a sold parts to
I believe Venezuela So. Am. i.e. the Magnet.
Also the 20 MEV deuteron unit that Chem. had in a small shed back of the
bookstore (now gone) .. it was glued together but worked very well.
The early LINAC in what then called Billings Hosp. (1951) To treat
patients with Beta particles (Linear Accelerator, Klystrons for RF &
3 magnet beam positioning magnet.
The Bubble Chamber.
Also at NW with Dr. Strait and his Statatron & Van de Graffs.
My brother was at U of C with Fermi. The Betatron & Cockroft Walton
which is now at Elmhearst Coll. i.e. John Erwood
You might like to visit my homepage:
Cheerio Bob K9AAU
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Subject: Tesla Coils
I just bumped into your web page (the Cyclotron - VERY nice work!). I'm
a EE in the Woodridge, IL area (about 3 miles west of Chicago), working
at Bell Laboratories. One of my hobbies is building Tesla Coils. I
belong to the Tesla Coil Builders Association (TCBA), and am very active
on a couple of Tesla mailing list sites. My current coil is a 10"
diameter one that outputs point-to-point discharges of over 5 feet.
I'm trying to locate others in the Chicago area that share the same
interest. Would you be interested in meeting others who build coils or
work with High Voltage projects?
Bert Hickman
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Once I got another Fred interested in the same stuff!
Subject: Hi Fred !
This is Fred your doppelganger in Windsor, Ontario, Canada.
as you do it seems I have too
I am an electronics tech in which I have a home operated business
repairing consumer goods. in my spare time I design and build my own
accelerators, high voltage spark generators and other high voltage
projects, I am heavy into particle physics and am presently working out
the finer parts of magnetic and electro-magnetic fields. I can send you
some photos if your interested.
I came about your web page by accident.. it was excellent...Thanks.
Wish you the best and good Luck with your projects, please consider
keeping me informed of any new projects that you may develop. Good Luck!
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Subject: Ask Fred!

Ok, despite an earlier, not so serious question, I have one that
actually pertains to physics this time. And, to make your life easier,
it probably has a pretty simple "yes/no" answer. So, the question is,
does the gravitational force propogate at the speed of light? I seem to
remember that it does, but I got to thinking not too long ago, and,
well.. Like, say, for example.. You have a weight connected by a
string to a scale (the type you hang things from). You hold the weight
so that its weight is exactly supported by your finger (so that any
lessening of the normal force would cause the scale to start measuring
something). When you let the weight fall, how long does it take for the
scale to measure it (ignore the fact that it's probably way too short to
actually measure it). Then expand this to something like galaxies
orbiting each other, where the lag time would actually be
non-negligible.. Whattaya say, Captain? Not exactly on the order of
cyclotrons, but I'm not exactly looking for an in depth answer..

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oh great guru, can you tell us how much wood, exactly, would a
woodchuck chuck if a woodchuck could chuck wood.
Please take into consideration the following variables: the woodchuck has dentures; He'd really rather be drinking pina coladas in the Bahamas than chucking wood; It's Saturday, and he likes to sleep in on Saturdays, so if you ask him to chuck wood too early, he may be a bit tired, and the rate of chucking (ROC) would therefore be reduced by a factor directly proportional to the amount of sleep deprivation, multiplied by an appropriate universal constant, with corrections for his relative velocity with the said wood; related to the last variable, we must also consider the fact that Fred (of "Ask Fred" fame) probably does not have a clue how much sleep your average woodchuck gets on a Saturday (or any other day of the week) (or is it night of the week? Are woodchucks nocturnal??), so we must also include a constant to account for this anomaly; finally, variables that we should have come up with but didn't.
We will instead lump all of these into one large unknown, reminiscent of the way physics and like disciplines are really done, and give it some inane name like the "we have no idea" constant or something.
Travis Fricke and Angela Fazzio

I seem to remember some formula in Mechanics 185... Ha Ha Ha!

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Sometime September, Dave wrote:
Does anyone have know how to make a plasma globe at home with easy to acquire materials? Please respond to dgrinnan. Thanks, Dave.

Hey Dave!
I suggest that you find the book "Build your own Laser, Phaser, and Ion Ray Gun" by Robert Iannini. He has another book, which may be more helpful, and easier to find, "Build your own Space Age Laser..." (I forgot the rest of the title).
Anyway- The theory behind the device is to create a plasma inside an evacuated globe. To do this, you need an RF current source, of high enough voltage to excite the gas molecules in the globe. A simple high voltage-high frequency supply hooked up to a large, clear, incandescent light bulb sometimes gives better results than the commercial models!
For up to a 12" globe, I have found that about 20-50kHz at about 12-20kV is plenty.

Good luck, and be SAFE!
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On Fri, 12 Jul. 1996, Johnny wrote:
> do you now what 52 factorial is
Yes, I just happened to have a calculator handy...

1*2*3*4*...*50*51*52 = 8.0658x10^67
Now... This was undboutedly a math homework question in which the teacher wasn't looking for an approximation. However, we in the world of science have little or no use for 68 digit numbers, and must use significant digits. I guess that's what you get for asking a physicist a math question!!!
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On Thu, 4 Sep 1997, Ade Morris wrote:
> Hi Fred
> I happened to be listening to music on some headphones and I happened to
> touch a plasma globe. The music in the Headphones stoped. Have you any
> idea's why this happened. Both the Globe and the HI-FI were plugged into
> the same double plug socket at the time.
> Also my daughter said that she recieved a shock off me whilst I was
> touching the globe.
> Please help..

This brings up an important point about high voltage devices such as a
plasma globe. Since the plasma globe operates at about 20kV, the plasma
inside the globe conducts a great deal of this high voltage to the glass.
Every time you touch the globe, you are coming in contact with the high
voltage in some small degree. I suspect that the high voltage traveled
through your body and into the headphones. The shock to the hi-fi system
was enough to kill the headphones. As for your daughter, she probably
felt the same shock that the hi-fi system felt. I suggest taking the
plasma globe back to the dealer, and asking for a refund or replacement
because the operator should not ever feel a noticeable shock, nor should
he/she have any other equipment fail as a result of its operation. Hope this helps.
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