Re: [Phys-l] Coriolis effect puzzlement

[John Denker <jsd@av8n.com>]

On 12/01/2011 02:32 PM, Bob Sciamanda wrote:

> Consider a bullet shot with a horizontal velocity in the space over a 
> rotating platform.  An overhead camera, fixed in space in an inertial frame,
> would record a straight line trajectory of this bullet. It sees no Coriolis 
> effect.          [1]

I disagree.

If you use the camera data to determine the path of the
bullet relative to the rotating reference frame, in 
accordance with statement [1], then there *will* be
Coriolis terms in the equation of motion.

OTOH if you choose to impose a *nonrotating* reference frame 
on the film, disregarding the rotating reference frame, then
there will not be any Coriolis terms ... but this is the
answer to a different question, predicated on contradicting
what it says in statement [1] about the choice of reference
frame.

> A camera rotating with the rotating platform would record a curved 
> trajectory, due to a Coriolis effect. If the bullet could leave a track on 
> the rotating
>
> platform, it too would have the Coriolis curvature. The Coriolis effect is 
> an inertial effect, due to the rotation of an observer's/recorder’s 
> reference frame.
>
> If the space fixed camera records a curvature, it must be due to some real 
> forces, certainly not a Coriolis effect.

Make up your mind.  Are you measuring things relative to frame
"A" (the rotating reference frame) or relative to frame "B"
(the nonrotating frame of the camera).

You are free to choose either A or B.  You are free to analyze
the situation one way and then re-analyze it the other way.
However, you are not free to mix-and-mismatch.  You are not
free to say you are doing one thing while actually doing the
other.