Shop Math: Finding the Center of a Circle - Kevin Caron

Uploaded by kevincaron on 22.12.2010

(Text on screen): Shop Math: Finding the Center of a Circle, Kevin Caron,
The Voice: Hey, Kevin. What are you doing?
Kevin Caron: Homework.
I had a question the other day on YouTube.
"How do you find the middle of a circle if there's no center mark?"
Do you know how?
The Voice: Nope. Not yet.
Kevin Caron: Come here. Check it out.
The Voice: Whatcha reading there, Kev?
Kevin Caron: Well, if you guys are anything like me, and you've been away from school for awhile,
some of the stuff tends to dribble out and be forgotten. Part of that's math.
Great, great book to have in your work area.
The Voice: What's it called?
Kevin Caron: Math to Build On.
All the formulas you need for, like, figuring out the center of a circle.
Figuring out the length of, figuring out how to do, figuring out how to bend.
All the formulas right inside one little book: Math to Build On by Johnny and Margaret Hamilton.
Get this over at Go check them out.
So, you want to find the center of a circle?
(I got this right from the book, by the way.)
Measure it. Twelve inches. What's the center?
It's got to be six inches somewhere, right?
The Voice: Yep.
Kevin Caron: You can take your pencil and you can just mark it at six inches.
Is that going to tell you right where the center of the circle is? Not yet.
Get you another mark at six inches.
Get you another mark at six inches.
Where all the marks meet up, there's your center.
The Voice: Well, that seems easy.
Kevin Caron: If you have a tape measure.
You want to cheat a different way?
If you happen to have a compass with a pencil or, like, a piece of chalk for working with steel,
you can get on the outside of your circle and just draw a line.
Come over to the outside of the circle about a third of the way over; a quarter of the way over. Draw another line.
One more, just to be sure. Do three of them.
Draw a line. Where they intersect, there you go. It's that easy.
The diameter. No; I'm sorry. The diameter, the circumference. If you take the diameter, divide it by two, you get the radius.
And that's that dimension right there, from the outside of the circle to the center.
Measure in three ways. Where they all meet, there's your center.
OK, class over. Back to work.
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