### Author Topic: Billiards and Physics  (Read 296920 times)

#### Fu-Kwun Hwang

• Hero Member
• Posts: 3062
##### Billiards and Physics
« on: January 29, 2004, 11:21:25 pm »
Registed user can get files related to this applet for offline access.
Problem viewing java?Add http://www.phy.ntnu.edu.tw/ to exception site list

This java applet show you how to use the law of reflection (for optics)in playing pool.
A ball bouncing off the bank of a pool table behaves like a light ray reflecting off a mirror.

There are two colored balls; red and blue.

How to play?
Set up an initial velocity for the red ball and
let the red ball knock the blue one into one of the six bags.

Click LEFT mouse button within the red ball and drag the mouse
to set the initial velocity for the red ball.

The ball starts to move when you release the mouse button.

Click the RIGHT mouse button to change the initial position for the red ball.

Try it and find out the physics behind the game.
(For collision between two balls, please check out 2D Collision)

The following is a flash demostration.

Registed user can get files related to this applet for offline access.
Problem viewing java?Add http://www.phy.ntnu.edu.tw/ to exception site list

#### Fu-Kwun Hwang

• Hero Member
• Posts: 3062
##### Email:
« Reply #1 on: January 29, 2004, 11:21:58 pm »
Subject: RE: Billiards and Physics
Date: Mon, 5 Mar 2001 09:38:53 -0500
From: John Botsford <JBOTSFORD@equitable.ca>
To: 'Fu-Kwun Hwang' <hwang@phy03.phy.ntnu.edu.tw>

John Botsford wrote:

>
> The law of reflection can only be used in billiards to
> approximate the angle of reflection for a billiard ball. Since
> the rails of a pool table are rubber, the ball will sink into
> the cushion to varying degrees depending on the velocity of the
> ball. This amount that a ball sinks into the cushion changes
> the angle of reflection. For instance, the faster a ball is
> moving when it hits the rail, the sharper the angle of
> reflection will be. The law of reflection is a close
> approximation only if the ball is moving relatively slowly. The
> other thing that affects the angle of reflection is the spin on
> a ball. In the case of the cue ball, spin is often purposely
> mparted to the ball by striking it off center in order to change
> where the cue ball will end up. As for object balls, spin is
> imparted to them by contact with other objects (balls and
> rails). This spin also changes the angle of reflection.
>

#### Fu-Kwun Hwang

• Hero Member
• Posts: 3062
« Reply #2 on: January 29, 2004, 11:22:37 pm »
Yes. It is true that the law of reflection is only an approximation of what really happened!
The effect of rubber and the spining effect also can be simulated
if we know the spring constant and apply conservation of momentum,
energy and angular momentum. But that would be too complicate to
the students who just learn physics.
The purpose of our animation is for teaching. That is why I
simplify the problem and the result are still very similar to what
Regards!

• Guest
##### topic41
« Reply #3 on: January 30, 2004, 12:16:10 pm »
Subject: Physics of Pool
Date: Wed, 07 Oct 1998 14:13:44 -0400
To: hwang@phy03.phy.ntnu.edu.tw
Hi, I just played around with your java applet for billiards and I was
wondering if you know of any good books and/or websites about the
physics of pool. Any information you have about the subject would also
be extremely helpful ... if you haven't guesses I'm writing a report on
the physics of pool.

Thanks,

• Guest
##### topic41
« Reply #4 on: January 30, 2004, 01:42:08 pm »
Subject: web page
Date: Mon, 5 Jul 1999 16:15:46 EDT
From: CLBlom@aol.com
To: hwang@phy03.phy.ntnu.edu.tw
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

• Guest
##### topic41
« Reply #5 on: January 30, 2004, 05:43:19 pm »
Date: Tue, 16 Nov 1999 14:00:04 +0100
From: TURESSON SVEN-ERIK <da97tuse@ing.hj.se>
Subject: Re: Billiard
To: Fu-Kwun Hwang <hwang@phy03.phy.ntnu.edu.tw>

Thank you for helping. We got som new wiews that helped us to
determine our misstakes.
"Group 12 of the OOP-course at HJ"
/Sven-Erik

#### lopa

• Newbie
• Posts: 5
##### topic41
« Reply #6 on: September 29, 2005, 08:41:07 pm »
Sir/mam
I want the java file of this applet
thanks

#### Blackninja

• Newbie
• Posts: 1
##### hOW MUCH THIS WEBSITE SUCKS.
« Reply #7 on: November 11, 2005, 01:53:17 am »
With 25 years of experience, I find it very sad that teachers have to rely on a poor website like this to educate their fine pupils. Unfortunately though, the future of the United States has to rely on such low quality teachers, websites that lack educational value, and endless amounts of work sheets. Well, My main point is that this website is terrible and no student should be subjected to it. Even though there are many html domains out there, this one however is a waste of valueable space, and should never see the light of day again.

#### fatkid

• Newbie
• Posts: 1
##### This applet is terrible material.
« Reply #8 on: November 11, 2005, 01:53:45 am »
I was told by a peer to visit this site and try this applet to teach my students about reflection. I was incredibly disappointed by the results. The applet is poorly designed, does not teach about reflection very well, and I found it offensive. I would really appreciate it if you focused more on quality than making offensive garbage like this so-called "Billiards" game. Billiards has no place in the classroom and I am glad that this website is so obscure that no one will ever find it unless they stumble upon it by accident. Please don't give me the excuse that you are a physicist, not a programmer, because we all have a responsibility to the children. Making applets lacking in educational value shows a lack of social responsibility and is deplorable in this regard. Please cut the crap and work harder.

#### Fu-Kwun Hwang

• Hero Member
• Posts: 3062
##### topic41
« Reply #9 on: November 11, 2005, 10:53:56 am »
I do not know why you registered with several accounts(with different user name, for examples: the above two mesaages are posted by you and you also post some other message with different username).

Are you realy a teacher? Could you tell me why you post the following message with another username on our forum:
[quote:296bbea393]Physics=Boring!!!!![/quote:296bbea393]
*** The above two messages and the quoted one are posted from the same IP within 10 minutes ***

If you are really a teacher:

I am sorry that you find our applets are useless for you students. I am also sorry that you feel physics is boring. I do enjoy the fun of physics very much!
I am willing to help you if you could tell me what kind of applet (in detail) you really want.

I did what I could to help and many teachers do find our applets helpful for their teaching. That is why there are so many mirror sites around the world.

If I find something is not good enough , I would not just complained about the situation. I will really do something to help (our children).

I will try to help you if you could tell me the design of an applet you think it will be good for helping student to understand the physics concept. :roll:

#### Fu-Kwun Hwang

• Hero Member
• Posts: 3062
##### topic41
« Reply #10 on: November 11, 2005, 12:37:30 pm »
The following flash movie shows how this applet is related to reflection.
I did not aim the target directly.I can aim at any one of the image of the target.
Look at the trajectory of the balls and you will see why it is related to flection.

#### Fu-Kwun Hwang

• Hero Member
• Posts: 3062
##### topic41
« Reply #11 on: November 11, 2005, 01:35:20 pm »
If the above two flash animations did not show up in your browser, please click flash1 and flash2

#### tarabelo

• Newbie
• Posts: 1
##### Re: Billiards and Physics
« Reply #12 on: February 22, 2007, 08:36:36 pm »
Dear sir,

Your page is really interesting. I wonder if it'd be possible to get the source code of the applet. I am interested in making a new applet for my classroom with more possibilities, as an example, with more balls interacting.

Best regards

Dr. Tomas F. Pena

#### Fu-Kwun Hwang

• Hero Member
• Posts: 3062
##### Re: Billiards and Physics
« Reply #13 on: February 22, 2007, 08:49:11 pm »
You should have received the source code now.

#### tam

• Newbie
• Posts: 1
##### Re: Billiards and Physics
« Reply #14 on: March 21, 2007, 12:18:49 am »
Dear Fu-Kwun Hwang,
I find out that your Billiard applet is very useful for learning reflection's concept .
I would like to have the source code if you don't mind; to learn more how to apply
the concept into programming.