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Old 11-18-2020, 07:06 PM   #21
DavidG
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Default Re: Cubic inch question

Some learned it as 2piR squared and others as Dpi squared; either way the answer comes out the same.
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Old 11-18-2020, 08:34 PM   #22
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Some learned it as 2piR squared and others as Dpi squared; either way the answer comes out the same.
David.....Believe me, I KNOW how smart you are. There's no disputing that fact..........PERIOD! But respectfully, "2piR squared" ain't gonna cut it. You've given me cause to take aspirin already trying to make YOUR formula work. So.....I believe you meant "pi(r)squared", or pi(r)(r). No?

And "D pi squared" doesn't seem to work, either. And Sir....I blow it every now and then, too! DD
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Old 11-18-2020, 09:00 PM   #23
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Default Re: Cubic inch question

I think David just made a mistake by including the words “squared”. Circumference of a circle is 2PiR or Dpi. But neither is squared.

Last edited by JayChicago; 11-18-2020 at 09:33 PM.
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Old 11-18-2020, 09:44 PM   #24
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Caught me guys! Man, getting old ain't no fun. Actually the two are equal, but you're right, not for the purpose at hand.
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Old 11-18-2020, 11:48 PM   #25
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Default Re: Cubic inch question

At the risk of offending some. A hillbilly decided to go to college to study math. He comes home on holiday. Ma asks what he learned in math. He says; "Ma, I learned Pi r squared". Ma says; "No no son, Pie are round".
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Old 11-19-2020, 12:01 AM   #26
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At the risk of offending some. A hillbilly decided to go to college to study math. He comes home on holiday. Ma asks what he learned in math. He says; "Ma, I learned Pi r squared". Ma says; "No no son, Pie are round".

... And cornbread r squared"
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Old 11-19-2020, 12:18 AM   #27
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... And cornbread r squared"
What if it were a cornbread muffin?
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Old 11-19-2020, 12:23 AM   #28
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As long as we're on the subject of "corny".
Ma does a little studying of her own. She asks; Alright son, what is 2 Pi R? The son thinks a minute and replies; "Why Ma, 2 Pie are better than 1".
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Old 11-19-2020, 09:46 AM   #29
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Default Re: Cubic inch question

the .785 method is not so much a function of Pi but it is in lieu of Pi when plugging the diameter into a formula. For example if the diameter is 4 you readily know the radius is 2. But if the diameter is 3.187 you might not readily see that divided by 2. Because you are squaring the diameter you need to divide Pi by 4 or 2 squared.
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Old 11-19-2020, 05:35 PM   #30
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the .785 method is not so much a function of Pi but it is in lieu of Pi when plugging the diameter into a formula. For example if the diameter is 4 you readily know the radius is 2. But if the diameter is 3.187 you might not readily see that divided by 2. Because you are squaring the diameter you need to divide Pi by 4 or 2 squared.
Hmmm...! Not so much a function of pi...? OK then, but ".7854" does just happen to be the quotient when performing the "function" of ascertaining what 1/4 of 3.1416 might be, or more simplistically....3.1416 divided by 4! I'm not sure that I understand what is in question here.

If I simply punch "3.187² X 4 X .7854 X 8 =" into the calculator (it took me about 6 seconds to perform), I don't have to worry about finding radii or any other details. That simple ".7854" becomes an integral part of THIS formula. This seems (to me) to be a lot simpler than having to first determine the figures necessary to extrapolate for the formula "πr²". And THAT only yields the area of the circle. Now, ya still have to figure-in the height for the volume, and then multiply by the number of cylinders. "My" way takes care of "pi", and ALL of that other superfluous BS....just to figure out how big your flattie (or your Chevy, etc.) is.

"Bore X bore X stroke X .7854 X 8 =" .....easy, peasy! DD
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Old 11-19-2020, 07:16 PM   #31
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Understanding how the .7854 was arrived at and knowing how it is calculated from first principles is the most important thing.
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Old 11-19-2020, 08:59 PM   #32
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Understanding how the .7854 was arrived at and knowing how it is calculated from first principles is the most important thing.
I UNDERSTAND where it came from. The best part is that it works oh so well, EVEN for those folks that MIGHT NOT understand the "whys". DD
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Old 11-19-2020, 11:14 PM   #33
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Who says one only remembers 5 minutes of what they learned in 5 years of college?
https://www.youtube.com/watch?v=kO8x8eoU3L4

Oh, and if you divide cubic inches by 61, you get liters so you can live in the modern world...
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Old 11-20-2020, 07:50 AM   #34
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I just usually divide by 60 to get litres; it's easier to do quickly in your head. Close counts in hand grenades, horseshoes, and now, engine displacement.
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Old 11-20-2020, 07:56 AM   #35
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Hmmm...! Not so much a function of pi...? OK then, but ".7854" does just happen to be the quotient when performing the "function" of ascertaining what 1/4 of 3.1416 might be, or more simplistically....3.1416 divided by 4! I'm not sure that I understand what is in question here.

If I simply punch "3.187² X 4 X .7854 X 8 =" into the calculator (it took me about 6 seconds to perform), I don't have to worry about finding radii or any other details. That simple ".7854" becomes an integral part of THIS formula. This seems (to me) to be a lot simpler than having to first determine the figures necessary to extrapolate for the formula "πr²". And THAT only yields the area of the circle. Now, ya still have to figure-in the height for the volume, and then multiply by the number of cylinders. "My" way takes care of "pi", and ALL of that other superfluous BS....just to figure out how big your flattie (or your Chevy, etc.) is.

"Bore X bore X stroke X .7854 X 8 =" .....easy, peasy! DD
You're still using Pi. You've just simplified the formula. Pi is the function as it relates to the circle.
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Old 11-20-2020, 11:21 AM   #36
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Default Re: Cubic inch question

"The number π (/paɪ/) is a mathematical constant. It is defined as the ratio of a circle's circumference to its diameter, and it also has various equivalent definitions. It appears in many formulas in all areas of mathematics and physics. It is approximately equal to 3.14159. It has been represented by the Greek letter "π" since the mid-18th century, and is spelled out as "pi". It is also referred to as Archimedes' constant.[1][2][3]"


From https://en.wikipedia.org/wiki/Pi which also has a neat graphic.
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Old 11-20-2020, 06:37 PM   #37
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You're still using Pi. You've just simplified the formula. Pi is the function as it relates to the circle.
No kidding?

Did I not mention something about "pi" back in post #11? I'm not understanding the overall point that you're trying to make here! DD
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Old 11-20-2020, 06:50 PM   #38
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Default Re: Cubic inch question

i am enjoying the Maths update lessons it sure takes me back.
Was there also a recent movie out called " The Life if PI".
I still enjoy doing mental numbers in the head to keep brain active.
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Old 11-20-2020, 07:56 PM   #39
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I am in awe of the math skills shown here. I once trimmed out the interior of a house that had two round turrets. Watching my progress , our high school's math teacher, who had taken a painting job for the summer, asked me if I would be willing to come to the high school on career day in the fall and talk to the students about how I use math in my job. Well about mid September he called me and outlined what I'd need to discuss in my 45 minutes. Yikes! all I could think of was the strings and nails and routers bolted to long plywood strips that I used instead of math. I ended up declining his offer, as I had spent a career teaching myself how to do my work without using math. Sometimes we can work around our shortfalls on a relatively simple task and get by. Just don't ask me to offset grind your merc crank to 4 1/8". I could not begin to understand the math involved!
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Old 11-21-2020, 05:25 AM   #40
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"Just don't ask me to offset grind your merc crank to 4 1/8"

If you can do that with a router and string I'd like to see it.
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