On May 26, 7:49*am, Danny D wrote:
On Sun, 26 May 2013 00:08:05 -0700, DD_BobK wrote:
Sometimes it takes more than a sentence or two to explain stuff.
Sometimes people who know aren't willing to spend the time.

OT warning

My dad taught me that if it can't be explained, it isn't
understood. For example, what a tangent?

Last week, a friend of mine wanted to doublecheck drawings
for trapezoidal-shaped windows where he needed an overlap
of 1/2 inch all around for the window glass dimensions:
*http://www4.picturepush.com/photo/a/...g/13133012.jpg

He had the numbers - he just wanted to doublecheck them.

He asked me how, and I came up with this simple formula
for the upper overlap (all other dimensions being purely
additive) given the symmetry of parallel lines, geometric
angles, & high-school trig:
*Side1=tangent of (90° + angle°)/2 * 1/2 inch overlap
*Side2=tangent of (90° - angle°)/2 * 1/2 inch overlap

He checked all his drawings with a calculator proclaiming
the answer correct. He then googled what a tangent was,
and apparently he got the answer that it's the slope at
any point of the curve.

He called me back, asking "What's a tangent?" because
the fact that it's the slope of a curve doesn't help
him understand what it is. Sure, he saw the graph of
a tangent on the web - but that didn't help him understand.

You know what I told him?

I said draw a one-inch right triangle with a 45° angle &
note the sides have a ratio of 1:1. The tangent of 45°
is simple the ratio of the opposite side over the adjacent
side. Now change the angle to 34° (which was his angle),
and you'll see the same ratio holds true. So you have
an equation where if you know two of the three components,
you can solve for the third. He understood.

I could have waxed and waned with using unit circles and
definition of the slope and describing sines over cosines
(like math teachers do); but, the answer (for him) was as
simple as the relationship of an angle to a ratio.

Note: He then tried to apply the tangent to degrees in
Microsoft Excel, which only uses radians, so I had to
explain radians to him; but I'll just leave that
explanation to your imagination.

Point is:
If it can't be explained simply - it's not understood.

Back on topic, now that I know the O-ring sizing scheme,
I can doublecheck my numbers.

More importantly, for the o-rings that I don't already
have the trade size for, I first measure the cross section
and that already tells me the series (as long as it's not
a boss seal). Then I measure the ID & I have the trade
size. It's that easy.

Plus, this method works for all o-rings in the household!
Learning is all the fun (the rest is just work).

And this counts as a "simple explanation"?

Even your explanation of "tangent" (if correct, I didn't bother to
read it carefully) hardly qualifies as "simple".

No disrespect to your dad but...he was wrong.

"My dad taught me that if it can't be explained, it isn't
understood."

I fully understand fourier transforms (classical & FFT's).
Can I easily / simply explain them? to you?
No... that's why there's a multi-week course on them AFTER a couple
years study of math.

I suppose I could explain them to you in a few dozens of hours?
Would that count?