If you square the diameter of a circle and multiply by .7854, you get
the area of the circle. Also,4 X 0.7854 = Pi. With a little
thought, you can get along without pi, if you want to....... Okay, "So
What?" you say.

That's the way I was taught to figure the displacement of an engine in high
school.

Bore squared times .7854 times the stroke. It's really not that different
from the normal way of figuring the area of a circle because .7854 is just
pi/4.

pi/4 * square(diameter) = pi * square(radius). (piRsquare)

In fact it's interesting that you mentioned it now because they were using
the same number on one of the auto TV shows last weekend. I think it was
Two Guys Garage.

Best Regards,
Keith Marshall


"I'm not grown up enough to be so old!"


"Pete & sheri" wrote in message
...
I found this in a 1908 Audel's Millwright's Manual.

If you square the diameter of a circle and multiply by .7854, you get
the area of the circle. Also,4 X 0.7854 = Pi. With a little
thought, you can get along without pi, if you want to.

Okay, "So What?" you say.

Well, note that .7854 means that a circle that just fits into its
enscribed square contains 78.54% of the area of that square. And
that's about 80%. So, an easy way to ESTIMATE the area of a circle in
your head is to simply think "8 tenths of the area of the enscribed
square = the area".

Example: A guy offers you a piece of steel just for coming and getting
it off the place RIGHT NOW!
You need to know the approximate weight of a 5" diameter bar of
steel that is 5 feet long, so you can decide whether you will be able to
lift it into your car trunk by yourself.

So, 5 X 5 = 25. 80% of 25 (in your head) is 20. That's area of the
circle. 20 X 60 (5 feet in inches) is 1200. There's the volume of
the bar! That's all there is to it!

Now for the weight:

A cubic inch of steel weighs 0.283 pounds think 2 Ate 3 (cannibalism
of numbers???). 0.283 is about .3

So the bar weighs 1200 X .3 = (in your head) about 360 pounds.
Sorry, Maybe you can lift it, but I'd have to pass on this one!!!

Well, maybe I could------


Pete Stanaitis