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: 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.

/htdocs/ntnujava/ejsuser/2/users/ntnu/fkh/twostarsequalarea_pkg/twostarsequalarea.propertiesFull screen applet or Problem viewing java?Add http://www.phy.ntnu.edu.tw/ to exception site list

**Press the Alt key and the left mouse button to drag the applet off the browser and onto the desktop.** This work is licensed under a Creative Commons Attribution 2.5 Taiwan License

Download EJS jar file(1267.7kB):double click downloaded file to run it. (29 times by 20 users) , Download EJS source (14 times by 9 users) View EJS source