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 Author Topic: Browian motion  (Read 105493 times) 0 Members and 1 Guest are viewing this topic. Click to toggle author information(expand message area).
Fu-Kwun Hwang
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 « Embed this message on: May 16, 2005, 02:55:49 pm »

Qualitative evidence of the microscopic nature of gases is shown by an effect called Brownian motion.
All the particles are moving with different velocity and in random direction.
The only interaction between partciles is coiision.
There is one larger particles which will be collide by surrounding particles and the behavior is similar to a random walk pattern.
This simulation let you get a visual representation of Brownian motion.
-*-

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Here is a related youtube movie

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noha khaled
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 « Embed this message Reply #1 on: November 27, 2005, 04:47:34 am »

[b:d5f38f5fff]Good morning,

I read that one of einstein's three papers published in 1905 is about browno\ian motion , it states that the perpendicular distance moved by a brownian particle is directly propotional as the square root of the time , for example in four seconds it moves 2 cm, in nine seconds it moves 3 cm and so on , so the body is slowing down , it is deccelarating , what is the reason for this deccelaration and what is the effect causing it , is it related to the soultion ??

Thanks [/b:d5f38f5fff]
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 « Embed this message Reply #2 on: March 25, 2006, 10:54:02 pm »

ie shows "no privilege"
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pyragas
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 « Embed this message Reply #3 on: April 02, 2006, 11:16:04 pm »

The new aplet for Brownian motion is very nice.
Can you send it to me for off line use?
Kestutis
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rhipple
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Relativity, Electromagnetism, Open Source Physics

 « Embed this message Reply #4 on: April 03, 2006, 07:15:48 am »

If you register with an email address, they will be emailed to you automatically
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Newbie

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 « Embed this message Reply #5 on: April 04, 2006, 06:57:15 pm »

i have find the :?:
i have the ZoomAlarm firewall
when i turn off it
all OK
the ejs is so great,it help me a lot
thanks Prof. Fu-Kwun Hwang and National Taiwan Normal University
you have done great work :!: :!: :!: ...
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sarig
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 « Embed this message Reply #6 on: July 24, 2006, 10:19:27 pm »

The applet is great. thank you

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Yves
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 « Embed this message Reply #7 on: September 21, 2007, 11:06:00 am »

Dear Professor and All,

Thanks.
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Fu-Kwun Hwang
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 « Embed this message Reply #8 on: September 21, 2007, 04:40:12 pm » posted from:Taipei,T\'ai-pei,Taiwan

Sorry! It should work now. Please try it again!
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Yves
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 « Embed this message Reply #9 on: September 21, 2007, 09:11:04 pm »

Thanks, Prof. Much appreciated.

This is a great site to learn about Brownian motion!
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lookang
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http://weelookang.blogspot.com

 « Embed this message Reply #10 on: March 19, 2010, 01:44:15 pm » posted from:Singapore,,Singapore

This is the best particles collision java applet i have ever seen.
800 particles and still not lag! it is incredible.
will study it carefully and add it here http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1455.msg5505#msg5505
Well done! credits to Francisco Esquembre and Fu-Kwun Hwang for this Best Brownian motion java applet
 « Last Edit: March 19, 2010, 01:51:45 pm by lookang » Logged
lookang
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http://weelookang.blogspot.com

 « Embed this message Reply #11 on: March 19, 2010, 03:29:05 pm » posted from:Singapore,,Singapore

Dear Prof,

Is it normal is terms of the computation that there is a small total kinetic energy (TKE) and total momentum (TMOM) lost in this model?

I hope i coded the TKE and TMOM correct.

Whichever solver Euler, Euler-Richardson, ......, QSS 3 etc there seems to be a small loss.

it that true? can i verify this model's has computation carried over error ?

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• Please feel free to post your ideas about how to use the simulation for better teaching and learning.
• Post questions to be asked to help students to think, to explore.
• Upload worksheets as attached files to share with more users.
Let's work together. We can help more users understand physics conceptually and enjoy the fun of learning physics!

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Fu-Kwun Hwang
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 « Embed this message Reply #12 on: March 19, 2010, 04:43:15 pm » posted from:Taipei,T\'ai-pei,Taiwan

Euler's method is only good for constant motion (velocity is constant).
Euler-Richardson or midpoint method is good for constant acceleration.

Normally, I use Runge-Kutta 4th order method, it is rough 100 times better resolution than midpoint error. This is good for most cases.
Sometime, I used Runge-Kutta Fehlberg adjustable time step method for interaction for like 1/r2 (when r is small , the error become larger).
However, you need to asjust time step carefully.
Smaller time will give you smaller run time error until run-offer error become major problem (10-6 for float, 10-13 for double).
If the particle size is very small , or there are many particels. the error will accumuate.

You need to study numerical method to understand what is the best way to used for different cases.

I would suggest you use Runge-Kutta 4th order method for most of the cases.
The error could be due to numerical method. However, it could be due to the coding.

You can calculate error if you know the theoretical value in advance.
Otherwise, it will depend on how much you know about the system to have a better guess.
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lookang
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http://weelookang.blogspot.com

 « Embed this message Reply #13 on: March 23, 2010, 10:40:43 pm »

I would suggest you use Runge-Kutta 4th order method for most of the cases.
The error could be due to numerical method. However, it could be due to the coding.

i was analyzing the codes and realized
Code:
public double getA (int i,double[] v) {
if(i==0)return 0; // b*v[0]; i removed the b*v[0]; because original used a speed decay constant b = -.25 i think
else return 0;
}

after i change it to return 0, the TKE is constant now!
cool! so it was the coding.
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Fu-Kwun Hwang
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 « Embed this message Reply #14 on: March 24, 2010, 07:44:08 am » posted from:Taipei,T\'ai-pei,Taiwan

The above code was designed for Browian motion, so a relatively large object was collided by many small particles. The larger object will experience some resistance when it is moving in a fluid, That is why I add a damping factor there. Sorry for the confusion.
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lookang
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 « Embed this message Reply #15 on: March 24, 2010, 11:12:17 am » posted from:Singapore,,Singapore

no problem, all is good
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smith88
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 « Embed this message Reply #16 on: August 18, 2011, 04:03:28 am » posted from:Dhaka,Dhaka,Bangladesh

You will find applets web pages translated into different language format here. You are all welcomed to translate our applet into your local language, please send me translated copy to share with more users.
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frodo
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 « Embed this message Reply #17 on: April 19, 2012, 01:53:12 am » posted from:NEW ENGLAND,NORTH DAKOTA,UNITED STATES

Lookang,

I like what you have done to the brownian motion applet. I was wondering if you could help me make an additional modification. I am trying to increase the number of Particle[0] to an array size so that the user can input a number of "yellow" particles say from 1 to 20 particles. I am having a difficult time doing this for I am a novice at the coding part of ejs.

Thank you for any help or insight you can give me.

Thanks

jake
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lookang
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 « Embed this message Reply #18 on: April 19, 2012, 11:37:53 am » posted from:SINGAPORE,SINGAPORE,SINGAPORE

hi jake,
are you referring to this
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1484.0
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frodo
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 « Embed this message Reply #19 on: April 19, 2012, 08:12:04 pm » posted from:Provincetown,Massachusetts,United States

yes, but i am not sure how my post ended up here. yes I am referring to the page you have linked. I am not sure where to incorporate your code and I was wondering how it would be possible to concentrate the yellow dots to the center of the view panel so that it looks like diffusion of a few particles moving from an area of high concentration...