Jodi Henderson on thu 6 apr 06
Mark,
I'm sure I've forgotten most of my geometry (beyond 6th grade) since I haven't had a practical use for it in my former lives as a psychologist or Montessori teacher of 9-12 year olds. I am finding more & more that I wish I did remember it.
Anyway...because I've forgotten most useful things about geometry, I was puzzled by your direction on finding the center of a circle: "Just get a string the length of the radius, and then scribe a circle arc from two places on the circles perimeter. Where they intersect is the centre. "
If you don't know the center, how do you know the radius? Or is there a way to find the length of the radius without measuring from a point on the circumference to the center point (or the ever-popular "Given" of high school geometry)?
I'd love to know, because it seems like something I'll need to know....daily I find something that I should've learned in school, but didn't that has now become useful to know in the studio.
Thanks,
Jodi
The Pottery Wheel Studio & Gallery
Newnan, GA
>
> From: Mark Tigges
> Date: 2006/04/06 Thu AM 11:39:28 EDT
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: ill-fitting lid + silly husband = power tool
>
> Well, a week ago, Belinda Willis ironically posted about her
> ill-fitting lid.
>
> I had the same problem. But I didn't damage my lid, I just put it
> together slightly unflat.
>
> Being a silly husband myself I opted for a powertool. I would have
> followed the plywood + sandpaper advice, but I had a good reason not
> too. (Besides of course the desire to plug something in.)
>
> So if you too have a fetish for power tools, and an ill-fitting lid,
> read about my solution ...
>
> http://www.m2crafts.ca/kiln/ceilingtrim.html
>
> Mark.
>
> --
> http://www.m2crafts.ca
> m2crafts [at] gmail
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
>
Mark Tigges on thu 6 apr 06
On Thu, Apr 06, 2006 at 08:22:46PM -0400, Jodi Henderson wrote:
> Mark,
> I'm sure I've forgotten most of my geometry (beyond 6th grade) since I haven't had a practical use for it in my former lives as a psychologist or Montessori teacher of 9-12 year olds. I am finding more & more that I wish I did remember it.
> Anyway...because I've forgotten most useful things about geometry, I was puzzled by your direction on finding the center of a circle: "Just get a string the length of the radius, and then scribe a circle arc from two places on the circles perimeter. Where they intersect is the centre. "
> If you don't know the center, how do you know the radius? Or is there a way to find the length of the radius without measuring from a point on the circumference to the center point (or the ever-popular "Given" of high school geometry)?
> I'd love to know, because it seems like something I'll need to know....daily I find something that I should've learned in school, but didn't that has now become useful to know in the studio.
Jodi,
In my case it was trivial, since ... I built the lid. I knew the
diameter of the lid. Or at least what I wanted it to be. I didn't go
to great pains to make it exact. Regardless, the radius is half the
diameter.
You asked "If you don't know the center (sic (I'm Canadian)) , how do
you know the radius?" Analytically, the circumference is
3.1415927*diameter, so you can measure the circumference by wrapping a
tape measure around it and dividing by 2*3.1415927. That will be the
radius.
But, if you don't know the radius, it's pretty easy to figure out
without math. The simplest way is to simply hold a tape measure on
one end and then sway it back and forth opposite to that side. And
you note the largest value. That's the diameter.
If you suspect (as was the case with my lid) that it isn't REALLY
round ... do it from a bunch of places and then average.
Either way, once you have the radius, you can use a compass (not the
directional aid, rather the geometrical instrument), or a piece of
string to draw arcs of a circle of that radius. The key is that the
centres of the arcs of the circle must be positioned on the edge of
the circle that you wish to locate the centre for. That way, the arcs
will pass through the centre.
Basically what it comes down to is that you have translated (moved) a
circle in some direction (by a length equal to its radius) such that
it's centre is on the edge of the circle where it used to be.
Do it on paper. Use a compass to draw a circle, then put the point
side of the compass on the circle you've drawn, then draw another
circle. Do this for more than one point on the original circle, you
will find that the subsequent circles all intersect at one point
(depending on your accuracy). That point is the centre of the
original circle.
I'm not so far removed from HS that I've forgotten everything, but in
all honesty, I think this is the ONLY time I have found immediate and
practical use for the constructive geometry that I learned when I was
14.
Mark.
> Thanks,
> Jodi
>
> The Pottery Wheel Studio & Gallery
> Newnan, GA
> >
> > From: Mark Tigges
> > Date: 2006/04/06 Thu AM 11:39:28 EDT
> > To: CLAYART@LSV.CERAMICS.ORG
> > Subject: ill-fitting lid + silly husband = power tool
> >
> > Well, a week ago, Belinda Willis ironically posted about her
> > ill-fitting lid.
> >
> > I had the same problem. But I didn't damage my lid, I just put it
> > together slightly unflat.
> >
> > Being a silly husband myself I opted for a powertool. I would have
> > followed the plywood + sandpaper advice, but I had a good reason not
> > too. (Besides of course the desire to plug something in.)
> >
> > So if you too have a fetish for power tools, and an ill-fitting lid,
> > read about my solution ...
> >
> > http://www.m2crafts.ca/kiln/ceilingtrim.html
> >
> > Mark.
> >
> > --
> > http://www.m2crafts.ca
> > m2crafts [at] gmail
> >
> > ______________________________________________________________________________
> > Send postings to clayart@lsv.ceramics.org
> >
> > You may look at the archives for the list or change your subscription
> > settings from http://www.ceramics.org/clayart/
> >
> > Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
> >
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
--
http://www.m2crafts.ca
m2crafts [at] gmail
Mark Tigges on thu 6 apr 06
Well, a week ago, Belinda Willis ironically posted about her
ill-fitting lid.
I had the same problem. But I didn't damage my lid, I just put it
together slightly unflat.
Being a silly husband myself I opted for a powertool. I would have
followed the plywood + sandpaper advice, but I had a good reason not
too. (Besides of course the desire to plug something in.)
So if you too have a fetish for power tools, and an ill-fitting lid,
read about my solution ...
http://www.m2crafts.ca/kiln/ceilingtrim.html
Mark.
--
http://www.m2crafts.ca
m2crafts [at] gmail
Carl Finch on thu 6 apr 06
At 05:22 PM 4/6/2006, Jodi Henderson wrote:
>Mark,
>I'm sure I've forgotten most of my geometry (beyond 6th grade) since I
>haven't had a practical use for it in my former lives as a psychologist or
>Montessori teacher of 9-12 year olds. I am finding more & more that I
>wish I did remember it.
>Anyway...because I've forgotten most useful things about geometry, I was
>puzzled by your direction on finding the center of a circle: "Just get a
>string the length of the radius, and then scribe a circle arc from two
>places on the circles perimeter. Where they intersect is the centre. "
>If you don't know the center, how do you know the radius?
OK, pay attention now, Ms Henderson!
First, you measure the diameter. Do this by laying your ruler (we weren't
allowed to use rulers in Geometry, if you recall--only "staight-edges")
across the circle. Hold down one end at one point on the circle (as
a pivot point), and swing the other end across to the other side of the
circle--back and forth--to get a maximum reading. That reading is the
Diameter.
Second (are you sitting down, Jodi?).............divide by 2...and
voila--the Radius!
>Or is there a way to find the length of the radius without measuring from
>a point on the circumference to the center point (or the ever-popular
>"Given" of high school geometry)?
Yes! Radius = Circumference/PI
(PI = 3.14159..., or, as passed into law by the Indiana legislature,
exactly 3 and 1/7)
>I'd love to know, because it seems like something I'll need to
>know....daily I find something that I should've learned in school, but
>didn't that has now become useful to know in the studio.
Aren't you glad you spent all that time in school learning those DSM codes
instead?! ;-)
--Carl
in Medford, Oregon
Carl Finch on thu 6 apr 06
In my response to Jodi Henderson I wrote:
>Or is there a way to find the length of the radius without measuring from
>a point on the circumference to the center point (or the ever-popular
>"Given" of high school geometry)?
"Radius = Circumference/PI"
My bad--shoulda been: "Radius = Circumference / (2 times PI)"
--Carl
Steve Slatin on fri 7 apr 06
Jodi --
The radius (length) is exactly half the diameter.
Take a piece of string and mark on it the length
that's exactly the widest distance across the
circle. That's the diameter. Fold it in half,
and mark the half-way point. That's the radius
(length).
Using the process below allow you to use the
radius length to identify the radius *point*.
Let me fulminate a bit here -- kids are forever
asking why they need to learn actual facts (like
how to solve for a variable, how to reduce
percentages to common denominators and so on).
Adults often foolishly brag that since high
school they never needed to know algebra, or
geometry, or history, or biology, or physics ...
But these things are all how the world works.
People who don't know anything about how the
world works sometimes they don't do too well in
dealing with it. People who are asked when they
need to know math should have some examples. My
younger son tried to give me the "you never
actually need to know math" argument a year or so
back and I took him to the studio and mixed
glazes with him. He never made the argument
again. He may grow up hostile to me, but he's not
going to be one of those proudly ignorant
adults I meet so often.
I don't condemn you, Jodi, you just happened to
be standing there when I reached a tipping point
... this is not an attack on you by any means,
you asked for a process you'd forgotten, and I
suspect you'd just forgotten a process from lack
of use ...
Best wishes -- Steve Slatin
--- Jodi Henderson
wrote:
> Mark,
> I'm sure I've forgotten most of my geometry
> (beyond 6th grade) since I haven't had a
> practical use for it in my former lives as a
> psychologist or Montessori teacher of 9-12 year
> olds. I am finding more & more that I wish I
> did remember it.
> Anyway...because I've forgotten most useful
> things about geometry, I was puzzled by your
> direction on finding the center of a circle:
> "Just get a string the length of the radius,
> and then scribe a circle arc from two places on
> the circles perimeter. Where they intersect is
> the centre. "
> If you don't know the center, how do you know
> the radius? Or is there a way to find the
> length of the radius without measuring from a
> point on the circumference to the center point
> (or the ever-popular "Given" of high school
> geometry)?
> I'd love to know, because it seems like
> something I'll need to know....daily I find
> something that I should've learned in school,
> but didn't that has now become useful to know
> in the studio.
Steve Slatin --
In the mornin’ cry of the rooster
The baby lay alone
And the old cow in the green grass
Shed white tears in the red hot sun
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Mary White on mon 10 apr 06
Yes Steve, math comes in handy.
Yesterday I wanted to experiment with small square serving dishes.
First I made a 7" square slab. Then I had to figure out what size of
an open-bottomed low cylinder I needed to throw on the wheel to make
the walls of the dish. I knew I'd learned this at some time but I
couldn't remember. I had to Google to get the answer.
The answer? The circumference divided by pi. So, 28" (4 x 7) divided
by 3.14159 etc means the diameter of my cylinder needed to be 8.9
inches. And it worked!
Mary
>
>Let me fulminate a bit here -- kids are forever
>asking why they need to learn actual facts (like
>how to solve for a variable, how to reduce
>percentages to common denominators and so on).
>Adults often foolishly brag that since high
>school they never needed to know algebra, or
>geometry, or history, or biology, or physics ...
>
>But these things are all how the world works.
>People who don't know anything about how the
>world works sometimes they don't do too well in
>dealing with it. People who are asked when they
>need to know math should have some examples. My
>younger son tried to give me the "you never
>actually need to know math" argument a year or so
>back and I took him to the studio and mixed
>glazes with him. He never made the argument
>again. He may grow up hostile to me, but he's not
>going to be one of those proudly ignorant
>adults I meet so often.
>
>I don't condemn you, Jodi, you just happened to
>be standing there when I reached a tipping point
>... this is not an attack on you by any means,
>you asked for a process you'd forgotten, and I
>suspect you'd just forgotten a process from lack
>of use ...
>
>Best wishes -- Steve Slatin
>
--
Mary White
on the Sunshine Coast, BC, Canada
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