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



Actually the misconceptions abound with respect to density/buoyancy.
1. Some HS seniors and college students in intro physics don't understand
that equal sized objects of different weights which sink cause water to rise
the same amount, so that experiment should be done. This is becomes
understanable between ages 7 to 9, but not before then. This a vital
component of scientific thinking.
2. Yes since they never see cream floating on milk they don't understand
which is denser. But those who like cream floating on espresso might know
this fact. Simple facts like this go away from common knowledge when the
relevant experiences disappear.
3. A huge number of students don't think air has weight, and they
practically never realize that air is touching things so there can be an
interaction.
4. Some students think that when something is floating there is no
gravitational force on it, so demoing this is a good part of a buoyancy ILD.
5. Some students think that if the Earth's atmosphere vanished, the
gravitational force would go away. And as a correlary the Moon has no
gravitational pull because it has no atmosphere. But astronauts can walk on
it because they have heavy boots.
6. Then of course there is the one that magnets attract metal. And since
cans are made out of tin, they are attracted by magnets. The experiment
giving them various materials such as iron steel, copper, al... To test is
very important. I suspect they have been told at one time that tin cans are
steel, with a coating, which might not even be tin, but I think this type of
practical fact has gone out of chemistry.

You may laugh at the idea of churning your own butter, but those of us who
are old enough to remember unhomogenized milk have memories of lots of
things that now seem outlandish. I grew up on a farm and when we purchased
it we had a 2 hole privy instead of a flush toilet. There was no bathroom
so we took baths in the kitchen sink once a week. When dad put in a real
bathroom, it was a luxury! We bought raw milk from the next door neighbor,
but pasteurized it after seeing his cleanliness practices. There were
people who had small butter churns, but I never saw them in operation. My
bedroom upstairs had no heat so sometimes it would get very cold so once a
snow storm ball sitting on a window sill froze and cracked. It would
occasionally get down to 40 below in the upstate NY area. There was even a
little 80 year old lady, Ma Higgins, who wore a mother hubbard, lived in an
old school bus, and chopped wood on shares for a living! She didn't knock
on our door; she just walked in. However, we never locked our doors. We
never felt deprived, and now I value having had unusual experiences.

Misconceptions about how things work are increasing as the number of direct
simple experiences are decreasing. In my HS virtually all boys took shop
and all girls took home ec. As a result we were all exposed to practical
measurement which should help increase thinking skills. We don't know the
actual thinking levels of our peers at that time, but we do know that in the
past 30 years thinking skills have gone down according to Michael Shayer's
testing. This may be because of lack of direct experiences supplanted by
electronic simulations that do not necessarily follow the laws of physics.

John M. Clement
Houston, TX


Is it still common to ask 'People which is Denser, Milk or Cream?'

or must we now ask it with oil and water?

I'll wager that this Misconception is still quite prevalent.


On Jan 31, 2014, at 9:43 AM, Bob Sciamanda
<treborsci@verizon.net> wrote:

And I used to milk the cows to get the milk, and then churn
the cream into butter by rolling a jar of it around inside a tire.