Re: Apparent Weight

[jmclean@chem.ucsd.edu (James Mclean)]

On Sun, 22 Feb 1998, Mark Sylvester wrote:
> Another question:
> ... but I
> guess the case in question is the force which is accelerating the escaped
> drinks trolley down the aisle to the back of the plane. OK, there seems to
> be no 3rd law counterpart for this force. 
> So back to me seated in front of
> my computer - I knock my coffee mug off the table and it falls to the floor.
> In class (not the GR class) I would say that the Earth is pulling the
> falling mug with force mg, and the mug is pulling the Earth back with
> exactly the same force. Does this mean that mg is not fictitious after all? 
> ...

Pay close attention to the frame you are using.
1) In the Earth's frame, only the mug accelerates; N3 seems not to work.
2) in the Earth-mug center of mass frame, they accelerate towards each
other; N3 works, so I guess that's an inertial frame.
3) In the plane frame, only the drink cart accelerates.
4) in the plane-cart center of mass frame, they accelerate... well, not
towards each other, but at least in opposite directions.  N3 seems to have
been repaired.

Now, I'm not about to suggest that frame #4 is inertial!  So what does that
do to frame #2....

-- 
--James McLean
jmclean@chem.ucsd.edu
post doc
UC San Diego, Chemistry