Angular momentum and Area

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 mathematic equation, we know

Area of a triangle = width * height /2

All the areas have the same height,

and the same width (=Vx*dt).

`Author¡GFu-Kwun Hwang, Dept. of physics, National Taiwan Normal University`
```Last modified :  <!--hide script from old browsers