circle? elipse?

Circles can be defined as special case ellipse, although it is an often argued point.
An ellipse has two foci and it can be said that a circles two foci are equal. A straight line is sometimes thought of as an ellipse.

so does that mean that all eclipes are not circles?

Of course. All circles are round. Ellipses are only round when they are circles.

Try this. Put one peg in a board. Attach a string around the peg with a loop, and tie a pencil on the other end. Swing the string and pencil all the way around and you will draw a circle.

Put two pegs in a board. Slip a loop of string around the two pegs. The loop must be longer than the distance between pegs. Use a pencil against the loop tight enough to remove the slack. Swing the pencil around the two pegs, keeping the string taut with the pencil. You well be drawing an ellipse, the proportions depending on how much larger the loop is than the distance between pegs.

You will see the difference.

Forget the pegs. Use nails. They will work the same - unless you pound them all the way in, of course. If you do, this demonstration won't help you draw anything.

Circles are ellipses with eccentricity zero.

eccentricity zero? whats that?

I believe that means regular as opposed to eccentric.

Just noticed your tag line. I like it.

i understand what eccentric means... you can have eccentric turning on a lathe (i.e. cranks shafts) and then you can have eccentric old men and women (i.e. the ones that sit live with 300 cats) but what would an eccentric zero be?

yea my tag... when ever i try to say something profound or intellegent i always end up stuttering over... and i usually end up shouting POO on you... the life of a lexdestic eh?

no interesting tag line to go with your rather interesting avatar?

Ah the joys, and agonies, of being dislexic. I used to work for a boss who had the condition. Some of our conversations were most interesting to those who came in in the middle of the conversation after we had worked out a conversational pattern we could use.

You recognize an excentric form thrown on a lathe, a crank shaft. The excentricity of the crank is measured from the line between the lathe centers, the main shaft, and the farthest throw of the crank. That would be some positive number.

An excentricity of zero would occur under the conditions of the crank being moved to line up with the center of the main shaft. That would also result in the crank merely rotating, but not cranking.

Now an explaination of an excentric zero on the other hand requires that I introduce you to my brother-in-law.

Kelly

lol, but i dont know your brother -in - law like that. :-D lol thank you i do have a better understanding of it now

This is a specious argument - to suggest that a circle can be an elipse.

An elipse can indeed by relatively circular. But as someone above has gasped - once the distance between foci has been reduced to zero there is no eccentricity - only circularity. One radius makes a circle, baby. It ain't no elipse.

A dancer doing a pirouhuette turns in a perfect circle even when both feet are over the same point an eliptical orbit would topple a dancer. Triple pirouhuettes would not be possible.

Someones reasoning is circular here if nothing else. Perhaps it's two people - in which case it is indeed eccentric reasoning and not circular reasoning.

Make a circle into an elipse and it is no longer a perfect circle.

didnt expect a reply to this one, almost forgot i posted it... but thanks for the reply... math always gives me a headache for some reason..... im more of a science kinda of guy... but questions just pop into my head ya know... and this was one of them...