z Old

Parsnips and plugholes . . .

Volume 15 Number 1, Spring 2002

Rhyme and Reason

Steve Donnelly

I decided to make a New Year's resolution this year: to stop being weird. It all began in the fruit and vegetable section of the supermarket where I was closely examining the parsnips as I always do at this time of the year, just before my final lecture to first-year Physics undergraduates on classical mechanics. As the final topic on my lecture course, I talk about Newton's conic sections as these link the mundane with the cosmic and serve beautifully to illustrate the simplicity that often underpins the apparent complexity of the universe. What are conic sections? Well, if you take a solid cone and slice it in four different ways the edges of the different cuts form a circle, an ellipse, a parabola and a hyperbola respectively and these curves are precisely the orbits of celestial bodies -- planets, comets and others -- as they move through the heavens. Parsnips are the most conical vegetable in my supermarket and are easily sliced and so I have been using them for several years to illustrate conic sections in my lectures. All very logical and reasonable, you might say; however, that view didn't appear to be shared by the young woman in a Tesco uniform who noticed me perusing the parsnips. "Can I help you", she kindly enquired. "No it's OK", I replied. "I'm just trying to find the most conical parsnips".

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