# Moving … the new fad diet!

Did you know that how much you weigh in your hometown is different from what you would weigh if you moved somewhere else? Since weight is caused by how much gravity is pulling you down onto whatever surface you’re on right now, it changes depending on where you are. If you’re on the moon, you would weight 1/6th your regular weight, because the moon’s gravity is 1/6th of Earth’s.

But it also changes for different locations on the Earth. You would weigh slightly less on the summit of Mt. Everest, because you’d be further away from most of the Earth’s mass. Or at least, further away from mean sea level, which is closer to where things are normally weighed. It’s even different depending on what city you’re in. If your scale is accurate to more than 2 decimal place, you should calibrate it with a standard mass when you move it far away.

So, if you want to weigh less, you can try going to Denver, CO, where you’ll be over 1 mile above sea level. Since you’re further away from the center of the Earth, you’ll weigh less. Not much less. And your mass will still be the same.

That’s right. Weight and mass are different things. Weight is how much gravity is pulling you down. Mass is how much matter you’re made of. So you’ll weigh less in Denver than New York (or Watchung), but your mass would be the same.

Yes, there is a conversion between them. 1 Kg is 2.2 pounds (really 2.205). And this time we are comparing apples to oranges, because grams is mass, and pounds is weight. I expect that this conversion is only valid at mean sea level at the equator.

All right, mean sea level makes sense, since that’s elevation which we just talked about. Why the equator? Because the Earth isn’t a sphere. It’s really an oblate spheroid. That means that it bulges out a little bit at the equator because of centrifugal force of its spinning. Earth’s equatorial diameter is 7926.385 miles and the polar diameter is 7899.9 miles.

I was inspired to write this post when reading http://what-if.xkcd.com/67/.