Re: [Phys-l] Coriolis effect

["Robert Cohen" <Robert.Cohen@po-box.esu.edu>]

Anthony, 

I don't know the background of your "kids" but I strongly suggest that
you explain this in the following "basic" terms:

1. Objects that are spinning will spin faster when the "stuff" is
brought together (as with a spinning skater; removing frictional
losses).  Do a demo on a turntable by spinning a student holding some
water bottles at arm's length and then see what happens when they bring
their arms in toward their body.

2. The Earth is spinning.  You may not notice it but it is spinning very
slowly (twice as slow as the hour hand on a clock; if you still have
such clocks available).  That means that everyone on the Earth that is
at rest relative to the Earth is actually spinning with the Earth,
including the air.

3. When the air, which is spinning, is brought together, it will spin
faster in the same direction.  By spinning FASTER than the Earth, we now
see it as a spin.

4. The center of a hurricane has lower air pressure than the
surroundings, leading to the surrounding air being pushed toward the
center.  If your kids have not had experience with air pressure and how
the air pushes on things, you'd need to develop this.

5. The Earth, when viewed above the northern hemisphere, is spinning
counter-clockwise.  Consequently, the hurricane will be viewed as
spinning counter-clockwise.

6. When viewed above the southern hemisphere, the Earth is spinning
clockwise.  Show them a spinning globe.  Which way it spins (CW vs. CCW
depends on where you are viewing it).  Based on this, ask them to
predict which way hurricanes spin in the southern hemisphere (where they
are called cyclones for the most part).  You could also ask them to
predict which way the wind should spin where the center is high pressure
instead of low pressure.  You could also ask them to predict the spin on
the equator.

I've done this with mildly MR kids as well as college kids.  They can
understand this, although each step needs to be developed (for example,
the different viewpoints in #5 is not obvious to most kids).

I would avoid the Coriolis explanation (the above is equivalent) or the
relative motion explanation (which leaves out some important physics).

Of course, if you are teaching upper-level physics students and mean to
impress upon them coordinate transformation and the like, then by all
means go that route.

Robert A. Cohen, Department of Physics, East Stroudsburg University 
570.422.3428   rcohen@esu.edu    http://www.esu.edu/~bbq 

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu
[mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Anthony
Lapinski
Sent: Thursday, December 01, 2011 6:01 AM
To: phys-l@carnot.physics.buffalo.edu
Subject: Re: [Phys-l] Coriolis effect

I think my confusion came from interpreting diagrams I see in books. Air
coming south (from the North Pole) will be deflected to the right/west
(clockwise). For hurricanes, I need to look at air moving north from the
fast-moving equator. Then the deflection will be to the left/west
(counterclockwise). I think this makes more sense now.

Forum for Physics Educators <phys-l@carnot.physics.buffalo.edu> writes:
> Relative to the earth's surface, winds are deflected to the right in 
> the northern hemisphere (which could be eastward if the wind is blowing

> to the north). When air moves into a deep low pressure center (like a
> hurricane) it initially turns to the right as it move inward. It also 
> picks up speed (because of the pressure gradient) - which enhances the 
> Coriolis effect and the rightward turning. It will keep picking up 
> speed until the Coriolis force becomes so large that it offsets so much

> of the pressure gradient force towards the low center that the air 
> motion is inward but almost circular in the counterclockwise direction.
>
> In the southern hemisphere the Coriolis deflection is to the right - 
> giving an overall  clockwise rotation about the low pressure center. 
> The pressure gradient is still inward.
>
> Bob at PC
>
>
> From: phys-l-bounces@carnot.physics.buffalo.edu
> [phys-l-bounces@carnot.physics.buffalo.edu] on behalf of Anthony 
> Lapinski [Anthony_Lapinski@pds.org]
> Sent: Wednesday, November 30, 2011 12:57 PM
> To: phys-l@carnot.physics.buffalo.edu; tap-l@lists.ncsu.edu
> Subject: [Phys-l] Coriolis effect
>
> I know that the Earth spins eastward, which deflects winds to the west
> (clockwise) in the northern hemisphere and to the west 
> (counterclockwise) in the southern hemisphere. However, hurricanes spin

> counterclockwise in the northern hemisphere and clockwise in the 
> southern hemisphere. I don't fully comprehend this. Maybe it's more 
> complicated than I think. Are there other forces at work here, or am I 
> just missing/misunderstanding something?
>
> Just trying to explain this in "basic" terms to kids and possibly do a 
> demo (e.g., using a marble and rotating turntable).
>
> Any ideas/activities would be much appreciated.