Re: [Phys-l] momentum dissipation?

["Anthony Lapinski" <Anthony_Lapinski@pds.org>]

Yea, and my "honors" (high school) students are in disbelief when I put my
finger in a beaker of water on an electronic scale, and the reading goes
up. Buoyancy and Arch Prin ideas are very difficult for students to grasp.
Let's face it, physics is arguably the most difficult (and fascinating!)
subject to comprehend for several reasons. Many of the ideas simple go
against "common sense" or what students have been told (prior knowledge).
Then there's the whole confusing language thing, with speed and velocity,
momentum and energy, temperature and heat, vectors, etc. And, of course,
the math element for problem solving. It's no surprise that students at
all levels struggle with physics, especially the conceptual part. And most
of the textbooks do not help in this regard, not that I could write a good
one.

Forum for Physics Educators <phys-l@carnot.physics.buffalo.edu> writes:
> > John C states, "Conservation
> > reasoning should have clicked in by then, but it usually does not.  Even
> > in
> > the senior year of HS there are students who have still not grasped
> > conservation reasoning."
> >
> > I ran into this very issue 3 weeks ago.  I am using McDermott's Physics
> By
> > Inquiry with some juniors and seniors.  They were working on water
> > displacement.  A group of 3 students had difficulty deciding if a
> > graduated cylinder must be emptied in between each trial.  They had a 50
> > mL cylinder with some water.  Measure the initial volume, placed an
> object
> > in the cylinder, measured the 2nd volume.  Then they could not decide if
> > they could simply add another object for the next test, or if they had
> to
> > completely empty the cylinder and start over.  It took a full 4 minutes
> of
> > discussion for them to reach the conclusion that they probably /could/
> > just add the water.  One student stated that while they probably could,
> it
> > would just be easier to dump the water and start over...
> > Normal kids.  Typically categorized as smart and hard working.
> What is really eye opening is the research done by Piaget on this topic.
> Generally below below age 8 as I recall they will tell you that the weight
> of an object will determine how high the water rises because it pushes up
> the water more.  They think that if the object is dropped into the
> cylinder
> that this will raise the water more, and if lowered slowly less.  You can
> then demonstrate that this does not happen, but they will come up with
> reasons why you did it wrong.  The paradigm is so strong that students
> will
> not believe what they see.  But he found that usually by age 9 the
> understanding of water displacement clicks in.  He did know that this type
> of understanding was culturally dependent, but he looked at students who
> were from an exclusive private school.  We now know that his markers of
> thinking do vary widely in age, and that some indicators of low level
> thinking persist into adulthood.
>
> So momentum conservation, or indeed any conservation principle will be
> difficult to understand until students have learned conservation
> reasoning.
> There are programs that teach such reasoning, but they rely on inquiry
> lessons and not on explaining or lecturing.  Unfortunately PER materials
> do
> not generally build in enough reasoning tasks aimed at developing the
> important types of reasoning.  But they are probably still better than
> conventional lectures.
>
> John M. Clement
> Houston, TX
>
> _______________________________________________
> Forum for Physics Educators
> Phys-l@carnot.physics.buffalo.edu
> https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l