[ExI] Fwd: scienceblind

William Flynn Wallace foozler83 at gmail.com
Sat Oct 14 15:59:31 UTC 2017


Thanks Ben - This makes a lot more sense to me.  If I push something with
enough force, then when I suddenly move my hand, it should come towards me,
right?  Hah.  Can't be right.  Have to make Newton consistent.  I like it.
 bill w

---------- Forwarded message ----------
From: Ben <bbenzai at yahoo.com>
Date: Fri, Oct 13, 2017 at 1:19 PM
Subject: [ExI] scienceblind
To: foozler83 at gmail.com


Hi Bill.

Excuse me for replying directly to you, but the Exi-Chat list seems to be
rejecting my emails nowadays. Feel free to re-post to the list if you want.

I've done some engineering courses, and they assume knowledge of basic
physics, naturally enough, including this concept of a Normal force, or
Reaction force, which I had the same difficulty with as you seem to be
having.

I'd object to my tutor along the lines of "if this beam experiences an
upward force from the support, how come it doesn't shoot up into the air
when it's cut in half?" The whole concept of an upward force is nonsense to
me, as it seems to be to you.

This also applies to Centrifugal Force. Physicists insist that there's no
such thing, it's actually 'Centripetal Force', i.e. an inward-pointing
force, contrary to all common-sense and experience.

The solution, I've finally decided, is that these ideas arise purely from
Newtons third law of motion ("any action produces and equal and opposite
reaction", in plain english), and the need to make everything, including
static loads, fit in to this law. So, if a glass is put on a table, it
exerts a force on the table, by virtue of gravity. If the 3rd law is not to
be broken, the table 'must' apply an equal and opposite force on the glass.
We know that there is no real force that the table exerts (where would the
energy come from?), it's a bookkeeping exercise really. But physicists and
engineers will insist that yes, there really is an actual force. I
reconcile this by thinking this is a 'virtual' force, that only exists
while the actual force applies, and as soon as the actual force changes, so
does the virtual, opposite one.

In the end, it seems to me, it's all about making the maths work out. The
important thing is, using this concept, we can succesfully design and build
structures that work.

If anyone can clarify, contradict (with clear, plain-english explanations)
or expand on, this view, I'd welcome it.

Cheers

Ben

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Subject: [ExI] scieceblind
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This book is just amazing.  I was never into developmental psych, and these
findings are just outrageous.

I have been mostly interested in cognitive errors, as you may have spotted,
and these are in children, but unlike the usual run of errors of adults.

Your son may be a bit too old to test for these things that I will be
sharing, but OTOH some of the intuitive theories were held by adults.

In fact, Ph. D. physicists showed evidence of the same errors found in
children, if you can believe that.

A surprise for me on every page.  Very lucid writing.  Method sections you
can easily skip.  Nature did not prepare us for this world - obviously.  We
learn, and we learn incorrectly.

This is worth your time.

In fact, I found myself in an error or two.  For instance, what he calls
the 'normal force' example consists of a table and book lying on it, and
says the table is exerting a force upwards on the book (or else the book
would be pulled through it by gravity, which I doubt in the extreme, as
both are very solid).  Upward force?  From where?

I also thought about something not in the book:  why does a helium balloon
rise?  Don't tell l me it's lighter.  My cat is lighter than I am and he is
not flying around.  The gas inside the balloon must be exerting pressure in
every direction, so the force cannot be from there.  Where is the force
here??

bill w
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