Comments/Suggestions in 1999 (1998/1997)

Subject: Thanks
Date: Tue, 26 Oct 1999 14:22:23 +0200
From: ISAAC David <>
To: "''" <>

This is just to say thanks for your java applet. I bought a vernier recently
and couldn't work out how to use, but then I found your applet and it all
became clear.


Subject: Re: Reaction time & car accident
Date:  Mon, 25 Oct 1999 20:33:42 +0100
From: "Ray Holloway" <>
To: "Fu-Kwun Hwang" <>

I am now studying the Relative Motion applet, it is most interesting to see clearly the things we notice in everyday life.I have had some holidays boating on rivers and I can picture the effects clearly as I use the applet.While driving a boat it's speed relative to the current is most apparent, particulaly when trying to moor.

Thanks again for such an interesting web site

Best Wishes  Ray Holloway

Subject: Reaction time & car accident
Date: Sun, 24 Oct 1999 21:00:03 +0100
From: "Ray Holloway" <>
To: <>


I have only just found your wonderful web-site & have tried the accident
experiment, it really is a good lesson for us drivers.Perhaps it should be
included in driving tests.
I had not appreciated the "knock on" effect until I noticed that although
I could stop in time those behind me could not.
I found that at 100 mph I had to allow 75 feet between cars for them all
to stop & even then it was not succesful every time.  A wet road would of
made it much worse.

Thanks for a very interesting site, although I have no formal education in
Physics I find it fascinating, so I am going to try the other experiments

Regards,  Ray Holloway

Subject: Electromagnetic wave propogation
Date: Thu, 21 Oct 1999 15:45:24 +0100
From: "Arif Zubairi" <>
To: "''" <>


I was recently scouring the net looking for a suitable picture to
demonstrate the orthogonal mode of an electromagnetic wave in an optical
fibre for a presentation on polarisation dispersion (my artistic skills are
nil). I came across your moving Java applet description of an EM wave and
was suitably impressed as its exactly the type of picture I'm looking for. I
was wondering whether you might have still pictures of the sort that I might
be able to post in a Powerpoint presentation. If you do I would be much
obliged. Thanks

Arif Zubairi

Product Engineering
Nortel Networks
External: %     0181 945 3720
ESN: %          730 3720
E-mail:  )

thanks kindly. Much appreciated.

Subject:  (no subject)
Date: Tue, 19 Oct 1999 12:55:52 -0600
From: Carlos Meraz <>

This is cool dud!!

Subject: applet
Date:  Fri, 15 Oct 1999 14:09:41 -0400
From:  Daniel Lemire <>

Good day,

I checked your E/M applet today. Maybe you can help me out...

When I set both E and M fields to zero, I would expect the particule to
move at a constant speed in a constant direction (or possibly stay still).

Yet, no matter what I do, it doesn't seem to work.

I am just trying to show to a friend that a charged particule standing
still in a magnetic field won't feel a thing... if there is not E field.
Your applet would be perfect... but it doesn't give the desired result.

Daniel Lemire

Subject:  Re: applet
Date:  Fri, 15 Oct 1999 22:11:30 -0400
From: Daniel Lemire <>
To: Fu-Kwun Hwang <>

Thanks for your quick reply!

Date: Wed, 13 Oct 1999 00:35:28 -0700 (PDT)
From: Alex Ladikov <>

Dear Fu-Kwun Hwang

Your sight is very very interesing and very very
helpful for us. If you like physics problems we can
send you what we have. We think that our relationship
can be very helpful for you and for us.

Sincerely yours, physics club of lyceum "Leader" Kiev
Ukraine(post Soviet republic)

Date: Sat, 09 Oct 1999 12:15:20 -0400
From: A Friend <>

nice page.

thank you.

Date: Mon, 4 Oct 1999 14:28:02 -0700
From: "Steve Tyminski" <>
To: <>

Cool Stuff!

Subject: Physics java applets
Date: Tue, 28 Sep 1999 22:42:16 +0100
From: "Charles Scott" <>

I have just recently discovered your web site in an article in "The Herald"
newspaper which is published in Glasgow, Scotland.  I have visited your site
and was very impressed with the work that you have done. I intend to get my
Physics students, who study at Kilwinning Academy, Scotland, to access your
site as part of their coursework.
thank you
Charles Scott

Subject: kepler motion applet
Date: Thu, 23 Sep 1999 06:00:13 -0700 (PDT)
From: lee taishen <>

Dear Mr. Hwang,

Referring to the kepler motion applet in the below
I find it very interesting. However, I have some
difficulties when using the applet.

1. For second kepler law, the area of the shaded area
and non-shaded area should be the same. However, there
is no data showing what the area is.

2. for third kepler law, i observed that there is no
indication of the period of the planet. There is this
T value indicated in the applet but it is not the
period. i would appreciate if you can explain what the
T value is.

thank you.

best regards

Subject: More Java suggestions
Date: Tue, 14 Sep 1999 14:38:08 +0100
From: Jeff Forssell <>
To: "''" <>
CC:  Claes Ahlin <>

Back in school after a tough summer. My 81 year old mother was visiting
from USA and fell down a stairs and needed help for the 2 months she was
here. Bad luck! Didn't get much done this summer. But the weather was
nice at least.

Hope you扉e had a good summer.

I was checking to see if you multimeter aplet could be used to see in
what situations it would be incorrect (parallell with a LARGE
resistance) but it didn't take that into consideration- it gave the same
reading at 2000 kohm as 10ohm.
See the accompanying picture.

While I惴 at it heres the interpreter for Q basic

in case you want to try the files I sent before.

I've been looking at Walter Fendts Javas. some are  quite illustrative.
One that wasn't was about the "radioactive decay series". Do you have
anything planned there?

I'd like to find an alternating current aplet that would show the charge
acculation resp magnetic field buildup graphically.

I sometime try to show my pupils a water -electricity anology where
pump=voltage spource
small or clogged pipe=resistance
double chamber with elastic membrane=capacitor
turbine with inertial load=inductance
That might be something that could make an interesting Java aplet

I put together a very rough sketch of  the C-L anology:

Jeff Forssell
personal homepage:
my village technology homepage:
Swedish National Institute for Distance Education (SSVH)
Box 3024      SE-871 03 H酺n飉and /Sweden
tel +46(0)611-55 79 48   fax +46(0)611-55 79 80
schools homepage

Subject: SV: re send multimeter plus more ideas
Date: Thu, 16 Sep 1999 12:40:29 +0100
From: Jeff Forssell <>
To:  "''" <>

Thank you!
The aplet seems to work very well.
Some minor problem and a couple of wishes:
1) if I change the range while the meter is connected, the measured
voltage is not updated. (Hmm I tried it again and now it works. But if I
reload the page and turn "ON" directly it reads 4,67V on 10 V range. If
I change to 50 V range,4,76V stays in stead of 4,95V  The Equivalent
circuit is updated directly.)
2) I would prefer a much faster component value change while
continuously pressing mouse <0.1s per change. One can always "fine tune"
with single klicks.
3) I would like a possibility of writing in R2 values also.
(4) Fu Hwang 1999 in lower left, in stead of 1998)

Subject: SV: SV: re send multimeter plus more ideas
Date:  Fri, 17 Sep 1999 07:46:05 +0100
From: Jeff Forssell <>
To: "''" <>
CC:  Claes Ahlin <>

Thank you!

I still have the problem with voltage update on changing range even on
the new aplet (i've tried in both NS 4.5 and IE 3.0).

with a newly opened page:
press ON
V= 4,76V   10 range
change to 50 V    V still 4,76         (equivalent circuit Rs update
change to 10 V    v changes to 4,95
change to 50   V changes to 4,76

The write in window for the values works well. I would (on behalf of
Sweden and some other countries) like even comma "," to be interpreted
as a decimal sign.

Other clarity wishes: prefix the box with "R2" when updating R2 and
suffix the box with "kohm" when R values being set.

V  [  ]
R  [  ]kohm
R2[  ]kohm

I think the current circuit would be easier to see if you had a wire
connecting rather than 2 ground symbols.

When the Rm box is not checked, it would be good for the Eqivalent
circuit to be altered perhaps like this:

Hope you don't think I'm complaining! I use your aplets a lot! I wish
someone would go through my stuff to help me develop it!

Subject: Very Nice ..... but....more ideas
Date: Sat, 18 Sep 1999 22:12:40 +0100
From: Jeff Forssell <>
To: "''" <>

Very nice!

But I still get the update problem when changing range (both IE 3.0 &
Nets 4.5). Have you tried as the FIRST step after opening the page? I
know that the problem goes away if I do a bunch of other stuff (change
values I think).

One other problem: I think that the multimeters that I扉e used have had
the red  lead positive when in the resistance mode (which makes it
easier to interpret when measuring on active components like diodes).  I
havesn't checked that in reality since I had the thought though.

Reviewing my own work:
I'm mainly interested in getting my web resources polished up for my
Swedish students which mean that it is in Swedish which makes it
difficult for  non Swedes to say much about it.

Subject: physics java applets
Date: Thu, 9 Sep 1999 09:14:43 +1000
From: "Seth Bell" <>
Organization:  Xref Pty Limited
To:  <>

I have been visiting your site this morning (found via AltaVista) and
playing with the java applets.

A great resource and very educational.  Thank you!

Seth Bell.

Subject: digit shit
Date: Wed, 1 Sep 1999 21:42:06 +0200
From: "Kjell Crafoord" <>
To: <>

hi there!

really nice java applet, though it took me some time to figure out
why it said wrong answer all of the time when i was completely sure i
got the right one. i had to type 1.0 mm instead of just 1mm, and that
was quite annoying. if you wanted a tip, i guess that is one. keep up
the good work!


Subject: Vernier applet
Date: Tue, 31 Aug 1999 10:31:42 +0100
From: Cathal Flynn <>

Dear Dr. Hwang,
        I have used some of your physics applets and I find them to be excellent.
Well done! At the moment in the Physics Department we are making changes to
our first year physics labs and would like to include your Vernier applet
in one of the labs in order to help the students learn to read a vernier
scale properly. Is is OK if we include the applet in one experiment?
Thanking you in advance,

Yours Sincerely,

Dr. Cathal Flynn
Department of Experimental Physics
National University of Ireland

Subject: mixing light-beam
Date: Sat, 21 Aug 1999 06:44:04 +0700
From: amrat chawla <>

Dear Sir,
Your mixing light beam applet is very very instructive. When I show to
my children they were amazed and understand easily of what they learned
at school but never get it clear. You know how schooling in Thailand,
education here is mostly memorising and answer question ! So we parent
have to help our children understand by external help. Your applest is
very helpful tool.

Thankyou for your contribution to people of the world.
With best rgds.
Amrat Chawla.

Subject: online interactive site
Date: Wed, 18 Aug 1999 11:11:06 -0400

WOW!!!!!!  Reflection and Refraction is WONDERFUL!!!!THANK YOU

Leslie Marra

Subject:demo for Antonio Nari隳 university
Date: Wed, 18 Aug 1999 07:03:00 +0000
From: (felipe ortiz)
your physicals applets are very good! i am a enginering sistems student here in
colombia, and i need the java applets愀ource code.

you can send at my address today.  Is urgent!

Subject: Very Nice Applet
Date:  Sun, 01 Aug 1999 18:34:25 -0500
From: Greg Hecht <>

Very interesting and educational java applet, sir.  My compliments.

I am not an astronomer but studied Kepler's laws years ago.  Your applet
is the best tool I have ever seen to allow one to grasp the concepts.
Thank you for creating and sharing it.


Greg Hecht, MCSE
The Riverpoint Group, Ltd.
Kansas City

Subject:  Help !
Date:  Fri, 23 Jul 1999 05:15:13 +0800
From: "StyleWan" <>
To: <>

Dear Sir,

    I appreciate the Physics animations from you very much !   I want to learn java so that
I can make my animations.  Would you please give me some guides by introducing
some reference books and related materials ?  Thank you very much indeed !!

P.S.  I am a Physics teacher.  I have certain programming knowledge of Basic and


Date: Wed, 14 Jul 1999 23:23:57 +1000
From: "Antony Tribbick" <>
To:  <>

Nice java applet..
Demonstrates very nicely what I was experimenting on with golf balls

Date: Mon, 12 Jul 1999 09:28:18 -0000
From: "Edie Dukek" <>
To: <>

Your entire site is wonderful!  Thanks for taking the time to make this
excellent information acccessable to my students!

Edie Dukek

Subject: physics sites
Date: Thu, 8 Jul 1999 22:10:16 -0700
From: "E. Ou" <>
Organization: California Institute of Technology
I really like your physics pages. Especially the java applets, those are
great. I know your pages are old and I don't know if you update them
anymore, but keep up the good work :)

Subject: web page
Date: Mon, 5 Jul 1999 16:15:46 EDT

Dear Fu-Kwun,

I appreciate your web pages:  Billards and Physics, and 2D Collision.
I am a high school science teacher, preparing to teach an "Integrated
Chemistry and Physics" class, and I anticipate using your web pages in the
classroom.  Thanks!

Carrie Doyle

Subject:  web site
Date: Wed, 23 Jun 1999 21:44:18 -0400
From: "Monty McGee" <>
To: <>

Thank you very much for this web site; extremely interesting.  I work with
physics, chemistry and computer programming, and find this very helpful.

Monty McGee

Subject: SV: SV: SV: Doppler applet wish (&propagation)
Date:  Mon, 7 Jun 1999 07:06:02 +0100
From:  Jeff Forssell <>
To:    "''" <>
CC:     Claes Ahlin <>

I am in a bit of a hurry with other things also, but I have looked at the
applets and they look good!

You made a very nice interface for seeing the reflection of different
polarized waves. Both numerical and visual without cluttering up the
previous features!
Jeff Forssell
personal homepage:
my village technology homepage:
Swedish National Institute for Distance Education (SSVH)
Box 3024      SE-871 03 H酺n飉and /Sweden
tel +46(0)611-55 79 48   fax +46(0)611-55 79 80
schools homepage
residence +46(0)611-22144

>Fr幩:  Fu-Kwun Hwang[]
>Skickat:        den 7 juni 1999 03:20
>Till:  Jeff Forssell
>Ang嶒nde:      Re: SV: SV: Doppler applet wish (& propagation)
><<Fil: Doppler.html>><<Fil: Doppler.class>><<Fil: propagation.html>><<Fil:
>Jeff Forssell wrote:
>> I notice that if I enter a user ratio in propagation, the top and bottom
>> field maintain the colors it had before, no matter whether the ratio is
>> more or less that 1. Maybe it would be good to have the optically more
>> dense media become gray.
>>   I see that you have put in the angles also. I thought of suggesting
>> that but I forgot to write it.
>> A new idea I got was is: could the intensity of the beam colors show how
>> much of the radiation is reflected and transmitted.  No big need, but it
>> would be nice, even if just approximate. But that would be complicated
>> because polarization comes in also. That would be a challenge! Maybe
>> better with a separate applet. But you have made some amazingly compact
>> versatile applets before. (Like the lens /mirror one!)
>Try the attached java applet and let me know if this is what you want.
>Pick p-wave or s-wave from the top left selection.
>> I think there maybe is a serious flaw in the doppler applet: example
>> with the default settings the wavelength is supposed to be 20. If I
>> measure on the right it is 20 and left it is 60   if i change the speed
>> to 4 the measured distance between wavecrests becomes: 42 38  which
>> seems to indicte that the wavelength is actually 40.  I' m in a bit of a
>> hurry until wednesday so I may have made a mistake.
>In my previous java applet, the distance between wave front is not necessary
>related to the wavelength. Those are wave front generate at fix time interval
> not necessary equal to period of the wave).
>In this attached java applet it is modified so that the wave front is
>with the same period of the wave. Try it and let me know what you think.
>I will try to add sound effect at the next release.
>But you will have to wait a few days,
>I will have to do other stuff first.

When I wrote a moment ago about a BASIC program I had and decimal
acceptance, I got to thinking maybe your applet could be expanded (or a
new one with similar components so It could replace this program for
practicing reading analog scale instruments:

It is written i Qbasic. (There is also less common scale where range 12
V is to be interpretted from a printed scale with 6 V as full scale-
I've seen similar things in reality but that aren't very common so I
might take that away.)
That I don't have more scale divisions depends on 2 things:
1) I want students to practice estimating tenths of scale divisions
2) lack of time (laziness?)

I m sending  this qbasic file  (and another on Vernier scale)
As a friend of "old" computers I have versions for CGA and Hercules
screens too

Jeff Forssell

Yes we really do use commas for decimals!  We even use (sometimes)
periods as thousand separators.

We do end our sentences with . though.

I was amazed to hear from you so quickly. I found myself wondering what
is the time In Taiwan? We are at 17 degrees longitude and taiwan at 120
so that should mean that when you sent your letter it must have been
around 6 pm your time. (I don't know if you use Daylight saving time

Both the class files were smaller than the old ones! How is that
possible? Did you do some code cleaning when you added features?

Were you able to open the Qbasic files?

Subject: Congratulations!!
Date:  Sat, 05 Jun 1999 10:18:27 -0300
From:  "Tarso F. Cassol" <>

Dear Mr. Hwang

I visited your WEB page with hte aplicattions on JAVA to demonstrate
some Physics
laws and I found it very interesting.
I would like to send you my congratulations for your work.
Perhaps my Physics students may use and learn more science with your
Sincerely, Tarso.
Physics Departament of Universidade Federal de Santa Catarina.

Subject:  Very exciting!
Date: Thu, 3 Jun 1999 21:53:43 +0400 (EET DST)
From: Derya Oktay <>

Hello I`ve visited your homepage, and I must say that I found very
wonderful and despite I did not see you or talk with you, I liked you,
thanks for your hardworking. I appreciate you, if you accept.
Good luck.

             Ege University
             Department of Computer Engineering
             Derya Oktay
             icq# 23349443

Subject:   (no subject)
Date:  Sat, 29 May 1999 20:41:04 EDT

Thank you so much for the creative and very effective physics applets.  I am
a high school physics teacher and I use them frequently on my physics pages.
L Woolard
 <A HREF="">Enloe Physics Web

Subject:   Physics Java Applets
Date:   Sat, 29 May 1999 15:42:27 -0700 (PDT)
From:   rhys hughes <>

Are your Physics Java applets for sale. I find them very interesting,
but due the cost of Internet phone calls (ie; in the U.K.) I'd rather
install them on my PC.

Thank you


Subject:  Doppler applet wish (& propagation)
Date:     Wed, 26 May 1999 08:25:32 +0100
From:     Jeff Forssell <>
To:       "''" <>

I like the doppler applet (as I do most of your Javas) but when I was
about to try to use the x,y coordinate display to measure the difference
in apparent wavelength on different sides of the source, I found that
the display changed to angle. Which is very good in some cases but it
ought to be easy to have both. Either i 2 windows or perhaps left click=
angle, right click=coordinates

Another wish would be that the "propagation applet (which I love!) could
have the top medium become darker than the bottom when it愀 n value is
greater and increase the choice of n1/n2 to include day glass about air
below. (I know and appreciate the possiblity to set the n/n ratio to
0.667, but if you feel like adding something I悲 appreciate the above)

thank you
Jeff Forssell
personal homepage:
my village technology homepage:
Swedish National Institute for Distance Education (SSVH)
Box 3024      SE-871 03 H酺n飉and /Sweden
tel +46(0)611-55 79 48   fax +46(0)611-55 79 80
schools homepage
residence +46(0)611-22144

Subject:   SV: Doppler applet wish (& propagation)
Date:  Fri, 28 May 1999 09:28:04 +0100
From:  Jeff Forssell <>
To: "''" <>
CC:    Claes Ahlin <>

Thank you! That was fast!

The doppler applet is more flexibla now. I would though prefer if one
could lefdt press and drag between 2 freely chosable points and get
delta x, delta y; rather than only distance from source.
 Another detail is that the y coordinate is negative upwards which is
not the most common matematically, though those distances aren't so

You might be interested to know that the doppler applet was referred to
in one of the questions in the latest National Exam in Physics. But we
aren't allowed to disclose the contents. (So erase this letter :-)  )

I assume the index.html page was in Chinese (It sure wasn't English!)

The propagation applet is perfect.  Whoops I just noticed that for large
angles of incidence, the incident beam became solid red!

Subject:  SV: SV: Doppler applet wish (&propagation)
Date:     Mon, 31 May 1999 05:43:14 +0100
From:  Jeff Forssell <>
To: "'Fu-Kwun Hwang'" <>

I notice that if I enter a user ratio in propagation, the top and bottom
field maintain the colors it had before, no matter whether the ratio is
more or less that 1. Maybe it would be good to have the optically more
dense media become gray.

  I see that you have put in the angles also. I thought of suggesting
that but I forgot to write it.

A new idea I got was is: could the intensity of the beam colors show how
much of the radiation is reflected and transmitted.  No big need, but it
would be nice, even if just approximate. But that would be complicated
because polarization comes in also. That would be a challenge! Maybe
better with a separate applet. But you have made some amazingly compact
versatile applets before. (Like the lens /mirror one!)

I think there maybe is a serious flaw in the doppler applet: example
with the default settings the wavelength is supposed to be 20. If I
measure on the right it is 20 and left it is 60   if i change the speed
to 4 the measured distance between wavecrests becomes: 42 38  which
seems to indicte that the wavelength is actually 40.  I' m in a bit of a
hurry until wednesday so I may have made a mistake.

Subject:  more ideas for doppler and propagation applets
Date:  Wed, 2 Jun 1999 09:29:17 +0100
From:    Jeff Forssell <>
To:    "'Hwang'" <>
CC:   Claes Ahlin <>

I just got an idea f顤 the doppler applet that I hope you will like:
[ ] listener       in top part

if someone checks in the box, the user can place a "listner" anywhere in
the window.
Whenever a wavefront passes him the computer makes a sound (a beep or
tick or something).
For example: I place my listner in front of the advancing source:
beep beep beep beep beep (then it passes) beep    beep    beep    beep
If I place my listener off to the side I would get a less pronounced
(what should happen when a supersonic "bang" arrives should of course be
some loud noise).

Another wish for the propagation applet:
increase the n1/n2 options with "diamond to air". I think people
tend to be fascinated by diamonds and they do have a spectacularly
high n value. (I saw that in another persons refraction applet, which
also included the possibility to show wavelength changes (also different
colors for the different wavelengths) but I prefer yours otherwise)

Thank you for your answer. I have a lots of tests to grade now at the
end of the term. Perhaps it is the same for you.

Subject:  Re: (no subject)
Date:     Mon, 03 May 1999 18:44:25 +0200
From:     Peter Brichzin <>
To:       Fu-Kwun Hwang <>

Hallo  Mister Fu-Kwun Hwang,

thank you very much for sending all the files. To get a
good multimedia lesson is very important for me,
because it would be evaluated. A good evaluation will
give me a job es teacher.

I tried to understand your program. It's not easy
because my knowledge in Java is very basic. My problem
is now:
If I want to change the power of r in aceleration or
force   F~ a ~ 1/r^2 to
F~ a ~ 1/r^x
then I have it to change in the method drivs of class
movingProjectile. (it works)
But this method never is called in whole
projectileOrbit.class. And to give a different exponent
to acceleration I have to give a argument to method
derivs (or are there other possibilities.

Is it possible that  derivs is callt in rk4.
Could you send me please or could you help me
in an other way with an idea to cahnge it.
Sorry that I ask you so much. Probably your time is
rare, but it would be a big help for me.
Thank you very much

Peter Brichzin

P.S: To get an imagination whatb I want I send you a
modified version: I added a Checkbox to change force.
But I can't get the connection between checkbos and
method derivs.

Subject:  Physics applets comments
Date:     Wed, 28 Apr 1999 12:56 -0500 (CDT)
From:     Michael Blackstock <>

Fu-Kwun Hwang,

    Hello, I am an amateur American physics enthusiasts.  Your physics
page has caught my attention and I would like to let you know they
are wonderful.
    Under Dynamics on 6. Circulation motion and Centripetal force, I
would like to know if it possible to change the velocity of the circular
motion and change both the weights on either end of the string without
changing it's radius?

Thank you,

Michael Blackstock

Subject:  Re: Physics applets comments
Date:     Fri, 30 Apr 1999 10:46 -0500 (CDT)
From:     Michael Blackstock <>

Fu-Kwun Hwang,

    Thank you very much for the adjustments you made to the following
request I sent you!


Michael Blackstock

Date:     Tue, 27 Apr 1999 23:05:21 +0100
From:     "Anthony Vinters" <>
To:       <>

I have found the tansverse and longitudinal waves. They are excellent,
exactly what is needed. Being able to show the the phases of particles
relative to each other is very useful.
I will be able to direct my students to your site so they can see for
Once again thank you for your efforts the results are most pleasing.
Rishworth School

Subject:  Re: Applets
Date:     Mon, 26 Apr 1999 23:44:29 +0100
From:     "Anthony Vinters" <>
To:       "Fu-Kwun Hwang" <>

Dear Fu Kwun Hwang,
I have received your applet. This is fine, the diagrams look exactly
right. I cannot run the applet as my email seemed not to contain any
software to animate the diagrams, only the pictures themselves. Can
you put this on your site so I can try it out?
Perhaps you would consider writing an applet to show a how a
 Transverse wave is made up of oscillating particles: this would be a
most valuable teaching tool.Also a Longitudinal wave to show how the
wave particles vibrate in the same plane as the plane of propagation?
Both applets would work well alongside your excellent SHM applet.
Once again thank you for answering my request, certainly material
such as this makes Physics much more enjoyable to teach and learn.

With very best wishes,
Anthony Vinters. Head of Science Rishworth School.

Subject:  Applets
Date:     Thu, 22 Apr 1999 18:20:15 +0100
From:     "Anthony Vinters" <>
To:       <>

Dear Fu Kwun Hwang
Thank you for the Applets, they are excellent! I have used them for teaching
my students about Simple Hamonic Motion and the Principle of Superposition.
Have you done one which shows the motions of particles within a Transverse
Wave and a Longitudinal wave? It would be interesting to look at the
particle motion and compare them within these two wave systems. If it were
possible to show the phase relationship between any of the particles even
better! Showing that any particles that are 2Pi radians out of phase with
each other are 1 wavelength apart is something that students can find
difficult to understand without the help of a moving model.
Once again thank you for all your work.
With best wishes:
Rishworth School

Subject:  Virtuel Physics
Date:     Tue, 20 Apr 1999 11:33:53 +0100
From:     S鷨en R鷮el <>

Dear colleque

Your site is vere good, but it is very difficult to load. It takes more than 30

Yours sincely

assistant professor  Soeren Roejel
The Technical University of Denmark


Subject:  Color, light, and shadow.
Date:    Mon, 12 Apr 1999 10:14:01 -0500
From:    "John Clement" <>
To:      <>

An applet that would be invaluable in teaching how light and color work
would be one that had a flashlight with different color filters red, green,
blue, cyan, magenta, yellow, clear.  Then the user could view various
objects in those same colors using the flashlight.  This would be an
illustration of how "classical" color reflection works.

Subject:  bravo from Italy!
Date:     Fri, 02 Apr 1999 18:38:10 +0200
From: (Pavesi Giovanni)

I am a physics teacher from Parma, Italy, and I had much appreciate your
applet, that I 'll use during my school lesson. Excuse my poor english,
but however congratulations and thanks for your good work!
                     Paola Pannuti

Subject:  Re: model for an idel gas
Date:     Tue, 23 Mar 1999 13:40:57 +0100
From:     Stefan Berger <>
To:       Fu-Kwun Hwang <>

dear mr. hwang

thank you for helping! now it works!

sincerely, stefan berger

Subject: Re: about your page in
Date:    Tue, 23 Mar 1999 16:19:43 -800
To:      Fu-Kwun Hwang <>


thanks 4 the help
my teacher liked the animation...!!!

and the rest of the class too..!!

once again thanks

Subject:  model for an idel gas
Date:     Mon, 22 Mar 1999 22:44:29 +0100
From:     Stefan Berger <>

dear mr. hwang,

i'm a teacher for physics in germany. this is the third time i launched
your site in the internet. but when i try out your applet i get problems
by changing the number of particles. always i'm trying to change this
value it doesn't change the number of particles in the applet. can you
help me?

sincerely, stefan berger, bochum, germany

Date:     Mon, 15 Mar 1999 14:51:24 -0600
From:     "Stan Treanor" <>
To:       <>

Great Demo, I'll use it with my students.
Stan Treanor

Subject:  Amazing Teaching Materials !!
Date:     Sun, 14 Mar 1999 05:52:21 +0800
From:     "StyleWan" <>
To:       <>

Dear Sir,

    I am a Physics teacher in a secondary school in Hong Kong.  I found that the java
applets in your web page are excellent teaching materials !!  It would be great to save
the applets for teaching.  However, I could not save the java applets (together with the
homepage) so that I can play them offline.  Would U please help me ?

    Thank U very much indeed !!


Subject:  thank you
Date:     Fri, 12 Mar 1999 14:52:00 -0500
From:     Dany Marquis <dmarquis@RDS.CA>
Organization: R廥eau Des Sports

Your application in java to learn how to read a vernier help me.

Dany Marquis

Subject:  Permission to link to your site
Date:     Thu, 11 Mar 1999 10:39:57 -0800
From:     cmcLean <>
To:       "''" <>

I would like to commend you on a wonderful site.  The Vernier site is informative and
fun. I wanted to get your permission to link to your Vernier from a Cumberland County
Educational Physics course website.  It was suggested to us that we get permission to
link to any sites so that we don't infringe on any copyright laws.  I appreciate your hard
work.. You can respond to
Thank -You for your time.
Carol McLean

Subject:  Physics or Fisica
Date:     Wed, 10 Mar 1999 01:03:52 -0700
From:     Pedro R <>

Mr  Hwang:

First of all, i would like to congratulate you about your PHYSICS HOMEPAGE.

I'm an 18 year old student from Mexico. I study Mechanical and Electrical
Engineering at the ITESM here in my country.

Now your are probably asking: so, what?

Well, i'm taking a physics class in which we have to make several different
kinds of thing on of them, make a HOMEPAGE and include some
links to virtual labs ans stuff like that.

I managed to link some of your applets to my page, that the whole meaning of
this e-mail, to ask for your permission to keep those links, or if you
disagree, just send me an e-mail, and i would gladly erase them.

You can check my homepage (that it hasn't been finished yet) at
and tell me your thoughts.

I would apreciate you could let me keep the links.

Saludos desde Mexico.

Subject:  E&M Waves
Date:     Tue, 09 Mar 1999 00:34:41 -0800
From:     Chun-Te Peter Wu <>

Hi Professor,
        I visited the your E&M website and I am very impressed with the animation
of the E&M waves.  I especially liked the rotations of axis.  Good Job

Subject: Typo found...
Date:    Mon, 1 Mar 1999 11:59:51 -0800
From:    "Chris Holden" <>

I happened upon your web site and noticed that the word "Beginning" is
misspelled (you have it as "Begining").  The URL of the page is:

I hope this helps.


Subject:  Your website
Date:     Fri, 19 Feb 1999 19:47:52 -0000
From:     "Bob Arkley" <>
To:       <>

Thank you! I know almost nothing about physics, but I have had a
great time playing with the applets on your website. I was actually
looking for some simple information for a 13 year old about how
gravity keeps the planets in our Solar System in their orbits, but I
soon forgot about that in the sheer fun of playing. Thanks again
Bob Arkley

Subject:  Thin Lens Java applet
Date:     Fri, 19 Feb 1999 18:00:24 +1100


I was looking at your applet for the thin lens and really liked it. I am new to applets and
often it is possible to download them so that you can use them off line but I couldn't
work out what to do to download your applet.

I am a secondary teacher and would really like to show it to my students. Would I be
able to get a copy of it please.


Pam Evans

Subject:  (no subject)
Date:     Wed, 17 Feb 1999 18:32:04 EST

I liked your sight.  And found it very informative.  Hands on experience works
better than just reading the info.  Thank you.

Subject:  Wow!!!
Date:     Wed, 17 Feb 1999 09:25:53 -0500

Your site is fantastic!

I teach high school physics and have been looking for good simulations
to use with my students! This one is a winner!

Very talented work! Keep it up and thanks!!!

Lars Wendt, Hunterdon Central Regional High School, Flemington, NJ .

Date:      Tue, 16 Feb 1999 16:27:13 -0000
From:      Brad Busch <>
To:        "''" <>

Your caliper java applet is cool -

Brad Busch
VP Engineering, Class1 Inc.

Subject: physics webpage
Date:    Tue, 09 Feb 1999 15:06:23 -0500
From:    Tony Montana <>

hey, you're really good. i like your webpages alot. our physics teacher
referred us to your pages, and i think they're pretty cool, especially
with the animations and interactive applets. and plus my mom's heard of
your university (i'm chinese), so rock on!

Subject:  your web-site
Date:     Mon, 08 Feb 1999 22:15:14 -0500
From:     Susan <>

I don't have any suggestions, but I think your site is really great and
I like your graphics.

Susan Irlbeck -- physics student in Raleigh, North Carolina, USA

Subject:  your webpage
Date:     Mon, 8 Feb 1999 20:55:47 EST

your webpage is awesome! my physics teacher, Ms. Woolard,
( assigned us your webpage as our homework tonite. you
have done a great job! thanks!

stephanie yeh

Subject:  your webpage
Date:     8 Feb 99 16:40:40 PST
From:     shefali oza <>

WOW!  my physics teacher (Mrs. Woolard) suggested your website as an extremely
useful tool to help us learn about oscillations and SHM, as well as other
physics concepts. your site really is truly wonderful and it is obvious that
you have put plenty of time into making it.  it has been very helpful in
clarifying some places where i was having difficulties.  i am so glad my
physics teacher gave me your website address and i would
like to congratulate you on such a wonderful job.
shefali oza (north carolina)

Subject:  Physics Virtual Labs
Date:     Mon, 8 Feb 1999 18:34:46 -0500
From:     "Tonran" <>
To:       <>

Hello, I am a physics student living in the US. My teacher gave our class
your web page address to help us learn about waves and oscillations. I thank
you for you taking the time to write the java for these demonstrations. They
helped me learn the material.

Thank you,
Brian Senter

Subject:  Too slow to be followed
Date:     Fri, 5 Feb 1999 18:25:49 +0530
From:     "Er. Ravinder Avasthi" <>
To:       <>

        Your applets are verry-2 good but your server is very slow
,forcing not to even approach your site.
                           thank you

Subject:  Java Physics Demonstrations
Date:     Fri, 5 Feb 1999 23:05:19 -0500
From:     "Thomas Del Rosso" <>
To:       <>

From the Fermat page: "I am not a professional programmer, I am a physicist."

....but you're pretty good at both.   :)

Great stuff.  Thank you for your work.

Subject: Physics Java applets
Date:    Thu, 4 Feb 1999 22:25:53 +0800
From:    "Tay Kian Hwee" <>
To:      <>

Dear Mr Hwang,

    Hi there. I'm teaching physics in a secondary school in Singapore. I've
found your applets very useful in my teaching but wonder if it is possible
for them to be downloaded into my computer so that I do not need to access
the internet everytime I wish to use them in my lessons. Would appreciate it
very much if you could make the applets available. Thanks.

Mr Tay Kian Hwee

Date: Tue, 2 Feb 1999 22:39:22 -0200
From:     "Marcilio Carneiro" <>
To:       <>

Hi Mr Hwang:

  I?m from Brazil I worked as Physics about 10 years ago and since
that time I had a  desire : to make softwares for Physics teaching.
The DOS interfaces I used to have forced me to give up. Last year
(after spendig some time learning Windows based programming) I
 restarted the project but once again I didn?t like the results. I
used Delphi 3.0 (Pascal Object Language) and made about 100 programs
( mechanics and eletricity) but when I saw your programs I felt even
more disappointed with the ones i had done . Yours are brilliant ,
fantastic . Don?t you sell them ? I?m interested in many of them.
One : sugestion: Don?t use weak green colors I hardly can see them .
For instance the one you used  in Vactor addition,
Thank you and congratulations for your excellent work (I wish I was
talented as you are)
Marcilio Carneiro

Subject: help for all
Date:    Fri, 29 Jan 1999 12:53:11 +0100
From:    Jose Villasuso <>

Dear Sir:FU-Kwun Hwang.

I am a High School teacher from La Corunha , Spain ( Galicia ) near

I realy like yours appelets of  Java  and I am used to work with them in
my classes.
If you don`t mind I would like to know if is posible for you to do one
about this:
A force pulling a block on a slope, and showing the forces growing when
you aplay diferents pulls.
Also it would be a plesure if you could do another  one: a block moving
in horizontal , changing the force angles when you pull the block, and
at the same time showing the celerity of the block. The most eficient
angle to move is when the  tg (angle) = coefficient of rubbing

Sorry for my english

I?m very pleased for having found your work, amazed work, which is very
useful for my students and also for me.
Before all, thank you very much for your work and help.

Pepe Villasuso

Subject: Kudos on your excellent site
Date:    Thu, 21 Jan 1999 11:28:26 -0500
From:    "Robert Craig" <>

Your Java Applets are of great use in showing elementary students some
of the basics of science. You are to be commended for your hard work and
Sincere thanks
Robert M. Craig
Talenetd and Gifted Coordinator
West Alexandria, Ohio USA

Subject: Re: Regarding your Cyclotron Applet.
Date:    Wed, 6 Jan 1999 14:32:25 +0000 (WET)
From:    Joao Manuel Henriques <>
To:      Fu-Kwun Hwang <>

Hi Again.
 First let me apologise for not responding sooner, but I was on vacation.
 Second, I would like to thank you for having sent the Source Code, it
really helped alot...
 Now it is my turn to help you out (if U want to), I made another program
that simulated: ' Attwood's Machine', since you dont have it on the list I
could send you a copy of it ..(it is in C though...)
 Let my know if you want it or not...BTW it also uses RK4, but it looks
diferent from your routine....

 Anyway thank you very much.

On Fri, 18 Dec 1998, Fu-Kwun Hwang wrote:

> Joao Manuel Henriques wrote:
> > Hi.
> >  I am a student of the University of Lisbon and I was a assigned a task to
> > simulate the cyclotron.
> >  It has been really hard to make something that actually resembled a
> > cyclotron, but i still cant make the electron spin according to the
> > frequency of the Voltage.
> >  Can you please help me out?
> >
> >  Here is what I need to know:
> >  -I calculated a formula that calculates Theta, but the center of the
> > circular movement is constant. In other words the Ray of the circunference
> > increases, but the center doesnt change like it should.
> >  Can you tell me the formula to theta?
> >
> This is not the way I did it. There is a better way to do it:
> If you know the velocity V and force (F=qVXB) at time t,
> you will be able to calculate velocity at t+dt;
> If you know the position and velocity of a particle at time t,
> you will be able to calculate next position at time t+dt.
> Repeat the above loop, you will know the next position and velocity at next
> moment t+dt;
> >
> > There is something else I want to ask.
> > Is there a possibility of you sending me the source code?
> >  I know this is an unusual request, but it would really make me understand
> > how the program really works. My source code is so complex that not even I
> > can understand it, and above all it doesnt simulate the cyclotron right.
> >  I would be very gratefull if you could send it. I promise I wouldn't
> > change the code and say that the program is mine. All I need to know is
> > how you did it.
> >
> >  Well, please e-mail me back with a response, preferably one with the
> > reply i want to get.
> >
> >  Thank you for your attention.
> >
> >
> >                      Joao Henriques
> >   
> The source code is attached with this e-mail. But you will need to know about
> the
> Runge-Kutta method to understand the rk4 class.

Subject: Physics of Light
Date:    Tue, 5 Jan 1999 21:13:57 -0400
From:    "Reg & Lori Coppicus" <>
To:      <>

        Enjoyed very much the physics of light showing internal reflection, and
diffusion of the laser.
I look forward to examining more related Java applications, but a very good

Reg Coppicus
Nova Scotia, Canada

歡迎批評指教! 電子郵件請按