Math and Art: The Art of the Ellipse

This is a cool article about how important the ellipse is to the artist.

http://opinionator.blogs.nytimes.com/2010/09/23/the-frisbee-of-art/

The author gives a nice, if long, explanation about the significance of the ellipse, but it basically boils down to this:  circles are everywhere. And often, when we are looking at circles, we’re looking at them atilt.  We see projections of the circle, and projections of circles are ellipses.

Think of it this way:  suppose you have a hula hoop and you hold it parallel to the ground.  The shadow you see is circular, but if you tilt the hula hoop, the shadow will change–into an ellipse.  I don’t have a hula hoop, so I made do with a spare key ring:

As the circular key ring is rotated, it becomes less parallel to the ground; the shadow becomes less circular and more elliptical.  And at the end, the ellipse vanishes–an ellipse eclipse!

(Half) Parabola in Nature

I have a nice watering can with a long, straight spout.  It’s good for watering tiny plants in hard-to-reach places.

It occurred to me that if I held the can so that the long spout were parallel to the ground, the water would probably come out in a parabolic path.  The running water would have a horizontal velocity component, and the vertical component due to gravity would create the parabola

So I took some pictures.

And after playing around with Geogebra for a bit, I had my parabola!

This isn’t quite as pretty as this parabola in nature, but it’s more parabolic than these water spouts at the Detroit Airport.

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