Angular momentum and Area

It might seem surprising that a particle moving

in a straight lines has angular momentum.

In the absence of a net external torque acting on a system,

its angular momentum remains constant.

During equal time interval, the radius vector from the sun

to a planet sweeps out equal area.

sweep out equal area? (with respect to any origin.)

A black dot will move freely from left to right.

Different color shows the area it sweeps out
with respect to some fixed points.

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!

E-mail : please click hwang@phy03.phy.ntnu.edu.tw

Author¡GFu-Kwun Hwang, Dept. of physics, National Taiwan Normal University

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