[quote author=Fu-Kwun Hwang link=topic=190.msg6894#msg6894 date=1279209120]
Are you in the U.S. for AAPT meeting now?
[/quote]
yes, it is from 17-21 july, here earlier to buy stuff and enjoy the trip.

[quote author=Fu-Kwun Hwang link=topic=190.msg6894#msg6894 date=1279209120]
I just created a quick [b][color=red]version[/color][/b] of what you might need.

You can drag the gray dot to different height.
The [u]string[/u] mode is what you want.

The following applet can be used to illustrate
1. conservation of energy
2. Collision between two particles. (two [b][color=red]particles[/color][/b] are the same mass in the current version. I will add options for different mass later).
3. Pendulum or circular motion in vertical plane.
[/quote]
it is awesome man! i will look at code soon