Re: [Phys-L] 3 act video physics problems?

[John Denker <jsd@av8n.com>]

On 05/07/2012 06:46 PM, James Cibulka wrote:
> I would like to make a few videos for each 9th grade modeling physics
> unit, however I don't want to reinvent the wheel (and probably do
> worse too!)

Making videos is hard, as you will soon discover.  This explains
the abundance of bad videos (and scarcity of good videos).

> Does anyone have a link to video files that are usable to answer an
> interesting problem?

I made a bunch of animations to show the time-dependence and other
features of various types of waves, including running waves, with
special emphasis on atomic wavefunctions:
  http://www.av8n.com/physics/wavefunctions.htm

Also if you want to see how visualization can be use to address a
genuine real-world problem, see the animations of flow around a 
wing, e.g.
  http://www.av8n.com/irro/profilo1a_e.html

None of the examples mentioned above has (or needs to have) a 3-act 
format ... but such things could be incorporated into a larger 
multi-act presentation.

==========

If you want to make a video, you could start by making a decent
Coriolis video.  This is a topic that should be covered in high
school physics, but the typical course says nothing about it ...
or (worse) says grotesquely wrong things.

Here is a Coriolis video that gets about 90% of the physics right.
  http://www.youtube.com/watch?v=_36MiCUS1ro
In particular, it uses two cameras (one in the rotating frame, one 
in the nonrotating frame), and the narration comes close to correctly
stating that the Coriolis effect exists in the rotating frame and not
otherwise.  OTOH I would have to give a C- grade to the production 
values.  I do recognize that making videos is hard, and all the 
other Coriolis videos I could find are worse ... but I'm not grading 
on a curve.

In particular, it would help to doll up the video with reference
lines or snail-trails to show that the trajectory in the nonrotating 
frame is indeed straight, while the trajectory in the rotating
frame is indeed deflected.  The shadow of the gantry in the 
aforementioned example almost serves this purpose, but not quite.
Some stop-motion or slow-motion would help also.

Obviously it is silly to analyze the Coriolis term without also
analyzing the centrifugal term.  The motion of a freely moving ball 
would be good, but you also need a shot of a ball hanging from a 
string, to show that the centrifugal field is just as real as the
gravitational field.

You might want to start by doing an all-software animation.  Call
it a software "model" because that's the trendy word.  Use this to 
practice your post-production skills, such as adding music and 
narration to the video.  However, it remains super-important to 
have video of the real experiment.  You can overlay the animation 
on the real video to see how they compare.

Making a decent video of any experiment is about ten times harder
than just doing the experiment.

=============

The Coriolis video is just one example.  There are literally thousands
of crummy physics videos on youtube already.  Just pick one and remake 
it to higher standards.

The interrupted pendulum is another example.  There are many examples
in this category already ... but you it would certainly be possible 
to redo it to much higher standards.  Basic requirements include (a) 
having a grid in the background, so that height can be readily 
perceived, and (b) considering all three cases:  The low-energy case, 
the high-energy case, and the intermediate (slack) case.  This problem 
can be analyzed in great detail using only high-school algebra and
physics.  You don't even need trigonometry.  See e.g. 
  http://www.av8n.com/physics/loop-de-loop.htm