Gerhard Fiedler  wrote:
>
> I don't understand how you get from force to momentum. In this case,
> neither the earth nor the plane have a vertical momentum. (Imagine the
> earth as large enough so that the non-flat shape of its surface doesn't
> matter.) So neither goes into the momentum preservation calculation.
>

That's wrong statement "neither goes into the momentum preservation
calculation" as the assumption "neither the earth nor the plane have a
vertical momentum" is wrong. They have variable momentums strictly
within momentum preservation low.

Imagine a plane is a molecule, air is molecule and Earth is a molecule
too. Plane and Earth will be playing ping-pong, a ball being an air
molecule. Clearly Plane and Earth will be experiencing variable
momentums. You can glue more molecules into each object, this will
affect numbers, but physics would remain the same - variable
momentums.
--=20
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