Re: [Phys-L] The Make-Believe World of Real World Physics

[John Denker <jsd@av8n.com>]

On 07/30/2013 12:26 PM, Anthony Lapinski wrote:
> I wonder what other areas in physics are "less contrived."

Here's a classic:  With the aid of a block and tackle, a small 
person can win a tug-of-war against a much larger person.
My father demonstrated this to me when I was about five years
old.  It made a lasting impression.

He pointed out that the low-force end moves a large distance
while the high-force end moves a small distance, so that
energy is conserved.

This is so simple that you can do it on the first day of
class, and it demonstrates some fundamental physics, and
it has practical non-contrived applications.  Real-world
applications include the transmission on a car, the gears
on a bike, winches for hoisting and dragging stuff, winches 
for trimming the sails on sailboats, transformers in the 
power-distribution network, et cetera.............


Also:  The physics of cars is obviously relevant and non-contrived.
There is a lot of physics in the panic-stop situation, and the
rule of thumb for "safe following distance" that is taught in 
driver's ed classes leaves a lot to be desired.  There's also
physics in steering and cornering, in why you need a transmission,
and in how fuel economy depends on speed and other factors.
And so on.  This is not first-day-of-class stuff, but you can
work up to it.
  Diandra Leslie-Pelecky
  _The Physics of NASCAR_
  http://www.amazon.com/dp/0452290228

As previously mentioned:  Standard topics include things like:
  -- physics of NASCAR
  -- physics of bicycles
  -- physics of airplanes
  -- physics of baseball
  -- physics of cooking
  -- physics of weather and climate
  -- physics of the renewable energy industry


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On 07/30/2013 01:03 PM, Paul Lulai wrote:
> > The this to which i was referring to as contrived was my added
> > questions. As it stands we disagree on you dvt question. Chris pushes
> > with a force of 50 newtons for 10 seconds. They have only 10 more
> > seconds to push. They must average 100 newtons of force. With what
> > force must they push to average 100N? One answer if we are looking at
> > Favg for change in p (need firce averaged over time). A different
> > Favg if we are looking for work done (need force averaged over
> > distance). This is a bad question. Additionally, who the heck cares?

We agree that's a hokey question.  Nobody cares about that
question.

> > If I want to scaffold problem solving I would choose something else.

Exactly.  There are lots of non-hokey questions to choose from.

There are even some non-hokey distance = rate * time questions.
One classic example involves the strategy for swimming out of
a rip current.  People care about that.  Lives depend on it.

There are also lots of realistic Ohm's law questions, which have
the same algebraic structure.