Insufficient gravity

10Mar11

Teenage Son was explaining to me the experiment he had done in his physics lesson.

“So I measured my weight in Newtons…”

“Hang on,” I interrupted. “Why don’t we always measure our weight in Newtons? Instead of Kilograms.” I like the sound of a Newton, a good traditional British measure, honouring our greatest physicist (so far).

“Because a Newton is a measure of weight and a kilogram is a measure of mass,” he explained patiently. “Your mass is constant, but your weight varies.”

“But my weight in Newtons is the same wherever I am,” I asserted (although privately I acknowledge that my weight does seem to have been varying, mainly by increasing over time).

“Only on Earth,” chipped in Mrs R, momentarily baffling me. “Your weight equals your mass times your acceleration. If you weren’t on Earth, your acceleration would be different.”

I paused. For an Earth second or two.

“What are the chances,” I said, pompously, “of my weighing myself anywhere else apart from on Earth?”

Later, I got out my calculator. I weigh about 814 Newtons. That’s a little excessive, but not too bad. If I want to lose a bit of weight, I shall travel to Mars. It is easier than dieting and my mass will remain constant.

 



4 Responses to “Insufficient gravity”

  1. 1 Mike S

    On the plus side, it doesn’t sound like you’ll be getting any cake on your birthday…

  2. 2 NumberN

    I’m sorry to inform you that your weight is different all over the earth, depending upon your distance to the planet’s centre (which varies not only with the altitude, but also with the latitude due to the non-spherical shape of the earth) and upon local geology.

    I would recommand that you weight yourself only at the equator, and definitely avoid doing so the closer you get to the poles.

    http://en.wikipedia.org/wiki/Earth%27s_gravity


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