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# Re: [Phys-l] Fun/cool unit conversion example?

Jeff Loats wrote:

I thought I would ask here to see if anyone had a neat unit conversion
example that left you with a sense of "huh, I didn't know that" or "that was
cool!" or something similar.

Convert to SI units:

((pi^pi)^pi)^pi picoparsecs per pi^pi plutoperiods

and Jeffrey Schnick wrote:

How many earth-diameters is it from here to the moon? I was surprised
at how few it is.

Interesting! Most people are completely flabbergasted at how *many* it is. I'd wager that not more than one person in a hundred who didn't already know the answer would draw a scale model of the Earth- Moon system with the Moon even approaching its correct distance from Earth.

I like to draw a model of the Earth about 1 foot in diameter on the far left end of the blackboard and have the students help me figure out what things like the altitude of jetliners, Mt. Everest, the first U.S. manned space flight, and the space shuttle orbit look like on that scale. Then I ask students to help me draw in the moon at at its correct distance. That always generates a few gasps! Then I'll have them consider whether they think the first flight to the Moon was a big deal or not. Finally, I'll have them consider what the Sun looks like on this scale (100 ft in diameter at 2 miles) or the next nearest star (half a million miles away) and ask them what they think about the idea of traveling there. The size of the galaxy becomes unimaginable on this scale, so, if you want to continue the trek outward, you need to rescale things.

John Mallinckrodt
Cal Poly Pomona