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Question for you mathmaticians.....

Odie

Odie

Panning for Montana gold, with Betsy, the mule!
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What is the formula for determining the circumference measurement of a circle with the diameter of X.....?

Pie R squared, or something like that?

thx, ko
 
odie said:
What is the formula for determining the circumference measurement of a circle with the diameter of X.....?

Pie R squared, or something like that?

thx, ko
Click to expand...

C = 2 π r

I end up Googling it every time
 
Multiply the diameter by pi

Or stated another way,

Twice the radius times pi
 
And in case you were wondering, the area of a circle is

Pi time the radius squared


A=πr2
 
Geometry, or as one of my high school teachers said 'gee-I'm-a-tree'. Little did I know what I would end up in...

robo hippy
 
AlanZ said:
Multiply the diameter by pi

Or stated another way,

Twice the radius times pi
Click to expand...

Thanks, Alan......

So, if the diameter is 10", then 3.1416 x 10 would be the distance around the circumference?

31.416".......?

ko
 
odie said:
Thanks, Alan......

So, if the diameter is 10", then 3.1416 x 10 would be the distance around the circumference?

31.416".......?

ko
Click to expand...

Not to derail the conversation--but you can buy what are called "pi tapes". Wrap them around a cylinder (like a pipe), and they give you the diameter.

Hy
 
John Torchick said:
I discovered www.onlineconversion.com to be a great help in figuring various things.
Click to expand...

Hy Tran said:
Not to derail the conversation--but you can buy what are called "pi tapes". Wrap them around a cylinder (like a pipe), and they give you the diameter.

Hy
Click to expand...

Hey many thanks, John and Hy........

Actually, all I needed was a good formula for calculations, plus a bit extra. This is in conjunction with a conceptual idea I have for making a dispenser for making my own double tape being discussed in another thread......

ko
 
Pi, defined

image.jpg

The area of this pi is eight slices. But if you're really hungry, cut into 10.
 
I had to use the formula the other day to try to figure out how to make my own McNaughton blades, and get segments of arcs. My daughter showed me the calculator on my smart phone. I don't like having it in the shop. Minimal dust danger, and high risk loss factor.....

Never heard of the circumference tapes. Neat idea.

robo hippy
 
By the way, I thought the title of this thread was pretty entertaining.

Considering that the concept of pi and basic formulas are introduced (depending on school district) somewhere between the 5th and 7th grade...

<ducking>

Perhaps it should have been titles "Question for any pre-teens..."

</ducking>

Just a life lesson for those who, when in school, insisted "I will never need math when I grow up".

Oh, and perhaps we should give up on Pi and switch to Tau (2 times pi) as it represents the ratio of a circles radius to its diameter...
 
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I prefer i (the square root of -1)

There is no need to limit oneself to rational numbers... woodturners have to think outside the box!
 
AlanZ said:
Oh, and perhaps we should give up on Pi and switch to Tau (2 times pi) as it represents the ratio of a circles radius to its diameter...
Click to expand...

Wait, isn't this the Tao of Pi?

480px-Yin_yang.svg.png
 
AlanZ said:
..... "I will never need math when I grow up"...
Click to expand...

Would you like fries with your π? How about super-sizing your π?

AlanZ said:
.... Oh, and perhaps we should give up on Pi and switch to Tau (2 times pi) as it represents the ratio of a circles radius to its diameter...
Click to expand...

OK, then, back to the fifth grade you go and no π for you ... the ratio of the radius to the diameter is ½ ( or 2 for the ratio of the diameter to the radius), no π involved in this ratio.

Never heard of using τ to represent 2π. Greek letters are generally reserved for irrational constants. If you were thinking of the circumference, then:

C = πd
for the diameter to circumference, or

C = 2πr
for the radius to circumference
​

AlanZ said:
I prefer i (the square root of -1)

There is no need to limit oneself to rational numbers... woodturners have to think outside the box!
Click to expand...

That's an imaginary number not an irrational number. But, yes, imaginary numbers are fine as well since woodturners (and other artists) speak of "negative space" ... gaaack (as Bill the Cat would say).
 
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Yes Bill,

I meant to type


.... Oh, and perhaps we should give up on Pi and switch to Tau (2 times pi) as it represents the ratio of a circles radius to its circumference ...

And also yes, I know that i is imaginary, my favorite kind of numbers.
 
Oh my aching head!!!

If I want more pie, then I don't even bother to slice it...... And yes, I could eat the whole pie, especially blackberry, or cherry, or strawberry rhubarb, or marrion berry, or apple, or lemon merrange, or key lime, or peanut butter chocolate cream, or so many others. Now I made myself hungry. May have to take a trip to the pie shop.....

robo hippy
 
robo hippy said:
Oh my aching head!!!

If I want more pie, then I don't even bother to slice it...... And yes, I could eat the whole pie, especially blackberry, or cherry, or strawberry rhubarb, or marrion berry, or apple, or lemon merrange, or key lime, or peanut butter chocolate cream, or so many others. Now I made myself hungry. May have to take a trip to the pie shop.....

robo hippy
Click to expand...

You sound like me...I never met a pie I didn't like! :D
 
Bill Boehme said:
Would you like fries with your π? How about super-sizing your π?



OK, then, back to the fifth grade you go and no π for you ... the ratio of the radius to the diameter is ½ ( or 2 for the ratio of the diameter to the radius), no π involved in this ratio.

Never heard of using τ to represent 2π. Greek letters are generally reserved for irrational constants. If you were thinking of the circumference, then:

C = πd
for the diameter to circumference, or

C = 2πr
for the radius to circumference
​



That's an imaginary number not an irrational number. But, yes, imaginary numbers are fine as well since woodturners (and other artists) speak of "negative space" ... gaaack (as Bill the Cat would say).
Click to expand...

You know what seems odd to me? Numbers that aren't divisible by two.
 
robo hippy said:
Oh my aching head!!!

If I want more pie, then I don't even bother to slice it...... And yes, I could eat the whole pie, especially blackberry, or cherry, or strawberry rhubarb, or marrion berry, or apple, or lemon merrange, or key lime, or peanut butter chocolate cream, or so many others. Now I made myself hungry. May have to take a trip to the pie shop.....

robo hippy
Click to expand...

Just be careful you don't increase your circumference...
 
Mark Hepburn said:
You know what seems odd to me? Numbers that aren't divisible by two.
Click to expand...

I'll get even with you.

What's really odd are integers that when divided by [SUP]τ[/SUP]/[SUB]π[/SUB].dont result in an integer.

And, I protest all this τ nonsense. Obviously, τ is just a diabolical instrument of demented mathematicians. As any rational fool can plainly see, Greek letters are reserved for irrational constants. An irrational constant can't be a multiple of any rational number.
 
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I swam a hard mile at the pool tonight. Exercise is like hot sauce, if it don't make you sweat, you ain't doing it right! Enough credit for at least one piece of black berry pie. Vegan, gluten free, organic, sweetened with agave, and all that stuff. It even tastes great.

robo hippy
 
A few more math jokes (for those of us who didn't take 5th grade math):

If God had wanted us to use the metric system, he would have chosen TEN disciples.
------------------------------------------------------------------------

A mathematician organizes a lottery in which the prize is an infinite amount of money.
When the winning ticket is drawn, and the jubilant winner comes to claim his prize,
the mathematician explains the mode of payment:
"1 dollar now, 1/2 dollar next week, 1/3 dollar the week after that..."

------------------------------------------------------------------------
There are 10 groups of people in the world: those who understand binary, and those who don't.
------------------------------------------------------------------------
The ark lands after The Flood. Noah lets all the animals out.
He says, "Go and multiply." Several months pass. Noah decides to check up on the animals. All are doing fine except a pair of snakes. "What's the problem?" says Noah.
"Cut down some trees and let us live there", say the snakes.
Noah follows their advice. Several more weeks pass. Noah checks on the snakes again. Lots of little snakes, everybody is happy.
Noah asks, "Want to tell me how the trees helped?"

"Certainly", say the snakes.

"We're adders, and we need logs to multiply."
 
Now to tie all these quantities together, we have the following identity that will be familiar to more serious mathematicians.

e^(i*pi) = -1

where is e is the natural log constant 2.71828... ,
i is the square root of -1 and ^ means "raising to the power of.
 
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