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Re: [Phys-L] [SPAM] Re: History Was: Re: Another Fluid/Density'Problem'



Unfortunately density requires proportional reasoning for good understanding
and most middle school or HS seniors do not have this reasoning skill.
However, teaching it in middle school is something that could be done as
part of a program to improve proportional reasoning. Such a program MUST be
done as guided inquiry ala Shayer & Adey. Schools should be using both
Thinking Science and Thinking Maths which use simple materials and improve
thinking skills. To do this the curriculum has to be sqeezed a bit to
accommodate the extra 80 minute lessons every 2 weeks. Some curriculum
items are actually covered in TS such as levers, so the regular class time
on such items could be omitted. It can not be turned into a curriculum
because each thinking lesson needs time to consolidate so they are given
every 2 weeks. This is inline with modern brain research which shows that
the brain is very plastic and learning produces neuron growth. It takes
time to do this, so 2 weeks appears to be the optimal time.

Actually knowing this fact about neurons, means that classes where gobs of
new concepts are introduced each period are pushing way too much. The
student is overloaded and does not have time to grow the neurons. It is
more than just knowing basic things. A lot of facts are contingent on
overcoming existing paradigms. Just telling them that magnets only interact
strongly with iron and steel, and weakly with a few other natural materials
(excluding exotic magnets), doesn't work if they have the paradigm that
magnets interact with metals. That paradigm is still there despite being
told the fact. So a lab where they predict first what will interact and
then testing the materials can be very helpful.

I do cover things about fluids and density in college, but I go beyond the
syllabus in that I get them to think about the basic ideas. So for example
I lift a table using suction cups, and then ask them to analyze the forces.
They think that suction cups are pulling up on the table. So I draw a
picture of a suction cup and ask what is in between the cup and the table
when I pull up. They realize it is a vacuum, so I ask how a vacuum can pull
something up when there is nothing touching. I also ask them what could be
touching the table that could exert a force on it. I am careful not to say
just push, though I might say pull or push. Eventually someone says air.
So then I have them draw the forces on top and on bottom. I am also careful
to make sure they draw no forces at the suction cups. Then of course why do
I have to pull up on the suction cups? After that we go on to buoyancy
which they do not understand beyond the fact that it exists, and they do not
connect it with Helium balloons. They ALL think the Helium is pushing the
balloon up. Even students in a calculus based course in college do not
understand air pressure!!!! Their reactions are the same as the algebra
based course, but a little quicker. Their ability to use math is somewhat
better, but not really good. Most still can NOT do the Miranda and Joey
problem by algebra, and forget part B for the algebra based course.
Actually many HS physics teachers are challenged by part B.

http://www.srri.umass.edu/mop/MOPSamples

Activity 16 (Miranda & Joey) is a good intro to using graphs and motion maps
for solving problems, or understanding motion.
Activity 46 is a wonderful ranking task that makes even advanced students
think hard. It is done at the very beginning before any problems. Some on
this list might find it a little challenging. I forgot it was online.

John M. Clement
Houston, TX




Thanks for sharing. Kids often don't know "basic" things. I
imagine fluids is not taught in most (regular) high school
physics classes.
But I'm sure (hoping?) most saw density ideas in middle school.

Of course, all the technology has only made matters. Hard to
learn about physics concepts (and how the world works) when
everyone is using iPads, cell phones, etc.