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 will move freely from left to right.
Different color shows the area it sweep out
with respect to some fix points.
Does 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).
Your suggestions are highly appreciated!
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Author¡GFu-Kwun Hwang, Dept. of physics, National Taiwan Normal University
Last modified :