### Author Topic: Angular momentum and Area  (Read 89580 times)

#### Fu-Kwun Hwang

• Hero Member
• Posts: 3062
##### Angular momentum and Area
« on: January 29, 2004, 04:05:18 pm »
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It might seem surprising that a particle moving

in a straight lines has angular momentum.
Conservation of angular momentum L = r X m v
In the absence of a net external torque acting on a system,
its angular momentum remains constant.
Kepler's second law states:
During equal time interval, the radius vector from the sun

to a planet sweeps out equal area.

Does a free particle moving in a straight lines
sweep out equal area? (with respect to any origin.)
Press start to start the animation, and let the show begin

A black dot will move freely from left to right.

Different color shows the area it sweeps out
with respect to some fixed points.
Do all the areas have the same size?

Click within each area and see what will happen.

Certainly, from mathematics equation, we know

Area of a triangle = width * height /2

All the areas have the same height,

and the same width (=Vx*dt).

### Another angular montum conserved simulation

The following is another applets show two mass object attracted to each other by gravitation force.
The gravitation force does not change angular momentum.

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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!

• Guest
##### topic147
« Reply #1 on: January 30, 2004, 05:52:49 pm »
Date: Wed, 08 Dec 1999 12:29:42 +0100
From: "Vito Babi? <Vitomir.Babic@guest.arnes.si>
To: hwang@phy03.phy.ntnu.edu.tw
Subject: URL=http://www.phy.ntnu.edu.tw/~hwang/equalArea/equalArea.html

Great! Thanks!
Babic Vito, prof.
phys. teacher ( college level )
Celje, Slovenia

#### minusquare

• Newbie
• Posts: 3
##### angular momentum and area
« Reply #2 on: November 11, 2006, 12:32:25 pm »

dear sir ,

#### Fu-Kwun Hwang

• Hero Member
• Posts: 3062
##### Re: Angular momentum and Area
« Reply #3 on: February 26, 2007, 12:20:30 pm »
It should work now!

#### gk8

• Newbie
• Posts: 2
##### Re: Angular momentum and Area
« Reply #4 on: November 18, 2007, 07:12:53 pm »
Hello,
maybe this is a stupid question - I've got your cource code for this applet, but I can't open it with my EJS to modify it's view...There is no xml file. What should I do?
Thx

#### Fu-Kwun Hwang

• Hero Member
• Posts: 3062
##### Re: Angular momentum and Area
« Reply #5 on: November 18, 2007, 08:11:20 pm »
Simulations I have created since 2001 were generated with EJS. However, simulations shown under JDK1.0.2 simulations category were not created with EJS. For example, this one. That is the reason why you dod not find the xml source.
It should not be difficult to create a simulation like this one with EJS. Try to play with it, I will try to help you if you have problem.  But you need to let me know what you would like to do and upload your source code.

#### 1993.bryan

• Newbie
• Posts: 3
##### Re: Angular momentum and Area
« Reply #6 on: November 21, 2007, 09:57:45 am »
Dear Fu-Kwun Hwang,

I have seen many of your applets and stimulations and I think they are great, especially the one on the vernier caliper. I hope you will create one on micrometer screw gauge, hopefully, with zero error as well, so that we will know how to handle with it properly.

Thank You,
Yours sincerely,
Bryan

#### Fu-Kwun Hwang

• Hero Member
• Posts: 3062
##### Re: Angular momentum and Area
« Reply #7 on: November 21, 2007, 01:56:58 pm »
Please check out Micrometer applet and let me know if that is what you need!

#### 1993.bryan

• Newbie
• Posts: 3
##### Re: Angular momentum and Area
« Reply #8 on: November 22, 2007, 04:43:07 pm »
Dear Mr Fu-Kwun Hwang,

That sure is another great applet, but I hope that it can be improved so that it can be more similar to the vernier caliper one, in which we are able to adjust it and key in the readings.
Furthermore, I really hope that there is an applet on how to read positive or negative zero error for faulty micrometer screw gauge and vernier caliper.
I greatly appreciate your work as they really help out a lot.  ;DForgive me for asking so much

Thanks a Million!

#### Fu-Kwun Hwang

• Hero Member
• Posts: 3062
##### Re: Angular momentum and Area
« Reply #9 on: November 23, 2007, 09:33:49 am »
You can adjust the Micrometer applet by drag the slider or drag and drop with your mouse.
However, you can only change in a finite range.
Because I am not good at drawing, so I use one of the image file for micrometer from the web.
However, I was not able to use full range setting.
May be I can create another applet similar to one of the flash animation at the same page.

Quote
I really hope that there is an applet on how to read positive or negative zero error for faulty micrometer screw gauge and vernier caliper.

Do you mean a non-calibrated micrometer or vernier caliper? (The reading is not zero when the distance is zero)

It will never be too much as long as the suggestion can lead to better teaching/learning for physics.

I am writing another applet to include the feature you have requested. I will post it when it is done.