I learned something about algebra today.

Tom

Tom

Well-Known Member
I'm sure many of you are way better at math than I am. I only graduated from highschool and was certainly not the valedictorian. My initial answer was 3 times, given that diameter was straight forward vs area of a circle. I paused this video at around 40 seconds to confirm my thoughts on paper. It never occurred to me that I had to add (or subtract) the radius of circle A into the formula until I watched more of the video.
 
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P

popper

Well-Known Member
6 oops, 3. Got a similar question in IIRC 4th grade. About the velocity of a person at the equator vs the arctic circle. Got to go visit the Principal on that one. We decided the question was worded improperly.
 
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JWFilips

JWFilips

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Absolutely fascinating! Thank You For Posting! When I worked at Keystone observatory 1973 to 1977 we did always use Sidereal time using our equipment! Fascinating how the differences are explained on paper!
 
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Ian

Ian

Notorious member
That's a good one to know, and essential to know when you're doing ratio calculations for threading gears and leadscrew feeds as part of engineering a feed system on a screw machine from scratch. Also essential for belt drive ratios.

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Tom

Tom

Well-Known Member
Ian said:
That's a good one to know, and essential to know when you're doing ratio calculations for threading gears and leadscrew feeds as part of engineering a feed system on a screw machine from scratch. Also essential for belt drive ratios.

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I never thought about belt drive ratios and really have no use for such knowledge, but that made me curious. Assuming a v belt, where would the reference point be? Outside diameter, inside diameter, or halfway in between?
After a bit of thought, it seems like the outside circumference would be the reference point?
 
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fiver

fiver

Well-Known Member
might be wrong but i ain't got all day to waste before making the next calculation.
all i need to know is whether to buy a 3200 rpm motor or the 2800 rpm motor to make my brass shiny, or to make my 10 speed go up a hill.
6 is close enough to 1.
i'm not calculating a pathway to Saturn by sling shotting around mars.
 
JBinMN

JBinMN

Member
I took the route of converting the circles into 360° segments.
Since 1/3 of circle A would be/equal 360°/3 = 90°, then to adapt the Circle B, divided into 360°, then divide that into 1/3 to account for circle A being 1/3 Circle B radius, I came up with 9 times the circle A had to go "full circle " to equate to Circle B circumference. I am likely incorrect. 3 times seems wrong to me. Just thinking on it.

I only went into the video for 1:10, just to make sure I would understood the question.
I have no idea for sure if I am correct. BUT... I explained how I got to the conclusion as explained above, & I reckon that it will be correct using the "New Math" they use today.
;)
 
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Tom

Tom

Well-Known Member
fiver said:
might be wrong but i ain't got all day to waste before making the next calculation.
all i need to know is whether to buy a 3200 rpm motor or the 2800 rpm motor to make my brass shiny, or to make my 10 speed go up a hill.
6 is close enough to 1.
i'm not calculating a pathway to Saturn by sling shotting around mars.
Click to expand...
Nope, you're not wrong. I really don't have any need for such calculations in my life either, but sometimes things like this grab my attention and OCD kicks in. While a calculator is quicker, I like paper so I can see if I've used a wrong number in my gazintas.
 
Tom

Tom

Well-Known Member
JBinMN said:
I took the route of converting the circles into 360° segments.
Since 1/3 of circle A would be/equal 360°/3 = 90°, then to adapt the Circle B, divided into 360°, then divide that into 1/3 to account for circle A being 1/3 Circle B radius, I cane up with 9 times the circle A had to go "full circle " to equate to Circle B circumference.
I only went into the video for 1:10, just to make sure I understood the question.
I have no idea for sure if I am correct. BUT... I explained how I got to the conclusion as explained above, & I reckon that it will be correct using the "New Math" they use tofay.
;)
Click to expand...
Not sure if I follow your methodology, but 360/3=120
 
JBinMN

JBinMN

Member
Tom said:
Not sure if I follow your methodology, but 360/3=120
Click to expand...
I saw the "radius" measurement in the video in the OP, and went with the radius in my head after seeing it. So, since I saw the radius of B being 3, the I kept that number 3 in my head as a number to divide by to get the revolutions.

As most folks it seems, per the video, many would come up with "3" times, as the answer, but the radius of "A' is 1/3" of "B" i just went with the 3 x 3 = 9.
All done in my head.

Didn't get out the slide rule or a pencil & paper, though. ;)
I wasn't a space engineer on the NASA Moon trips, so there is that. LOL ;)
But I am the son of a Mech. Engineer & still have "some" brain cells left on occasion, depending on the subject. If that might make a difference..

BTW... Cheers~! :)

Hey.. I thought I did pretty well this late in the evening. ;)
 
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JBinMN

JBinMN

Member
P.S. - Yes, 1/3 of 360° = 120°. not 90°.
I reckon I messed up in the typing, but I was trying to type & do arithmetic in my head at the same time.
Can ya GImme a break?
;)


If not.. oh well, Not gonna lose sleep on it.
 
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Ian

Ian

Notorious member
I didn't watch it either but from the thumbnail rB is given as 3, but it could be any value. Given nothing I would use 3 also since it is the simplest whole number to use in the 1:3 ratio. So if rB=3 then rA=1 and dA=2 while dB=6. Then 2piX=6Pi where X is the number of circumferences of A that are equal to one circumference of B. Simplify piX=3pi, divide both sides by pi, X=3.

That's why I only made a 1490 on the SAT.
 
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JBinMN

JBinMN

Member
I can't even remember any PSAT or SAT scores in the 70s I might have made just about 50 years ago, (<Wish I could, but the years have taken their toll on remembering that sort of stuff. ;) ),
but I have to admit that I did make a homemade chicken pot pie tonite out of leftover cooked chicken, a can with some mixed veggies & a can of Cream of Chicken soup all mixed together as a filling, with a home made crust made out of 2 cups all purpose flour, 1/3 cup oil, 2/3 cup milks mixed together & then rolled out on wax paper in two parts. One, about 3/5ths being the base crust & the other 2/5ths being the top crust.
Put the filling in the base, and put the top on, crimped, slit & poked some holes it it for steam relief, & then stuck in the oven that was temping up as I made the pie to 375° F.
Put it in for 30 minutes & a chicken pot pie came out 5/5ths.
;)
Unfortunately there is only 2/5ths left , as my Missus ate 1/5th, and them took another 1/5th for lunch tomorrow & my youngest son stopped by and grabbed another fifth of pie for his 11-7 shift. For some reason the pie got cut into 5ths, instead of 1/4s, 1/6ths 1/8ths, or 1/3rds. I like to think it is because the pot pies I make are homemade & pretty tasty.
;)
Anyway, I might get my arithmetic "off", ( as well as making "{typos") once in a while but I make a damn good Pot pie and I mean well.
;)

Ooops.. Uh oh... A couple 5ths of Thread drift.

My apologies to anyone who might be troubled by my "ramble" in this post LOL :D
Maybe I should go have one of those 5ths of pie that are left. :)
 
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