Friday, January 23, 2009


Edit: I mistook which way things went as far as latitude vs. gravity goes, so I had to fix it.

This is absolutely exciting and amazing: we changed gravity yesterday!


You probably all know that gravity changes with height, right? The farther you are away from the earth, the less you way?

Well that is not the only thing that affects gravity, or I should say the gravity constant of your perceived weight.

You all know that you weigh less the farther you go from the earth now(I just told you above, so you should know). But you don't actually lose anything from your body, right? No. That is because all the stuff of your body is actually the mass of your body, and that doesn't change.

Weight is the mass of your body times a gravity constant. And the gravity constant gets smaller the farther out from the earth you go. That's why you "weigh less".

But there is another thing that changes the gravity constant. And that is the rotation of the earth.

If you take a string and attach some object to it (which has a mass) and then swing the the string around and around, you can feel the object "pulling" on the string (there are physical laws explaining why it does so). We have sort of created a "weight" of the object.

You see, the earth is split up into a number of latitudes (the horizontal lines that go across a globe). And at each latitude, the ground beneath you is rotating at a different speed (too long to explain now, so sorry if you didn't know that before).
And we are attached to this earth through the friction that comes up through our feet.

So here we are spinning on this earth but the speed at which we are spinning changes depending on where on earth we are. And like that object on the string, our "created weight" changes with that rotation.

So the gravity constant isn't constant all over the earth even if there were absolutely no mountains or anything tall (the height piece of gravity).
Generalizing, we could say it is only at the standard at the North Pole and the decreases down to the equator.

If the earth spun faster we would eventually all fly off and that would solve our over-weightness problem in the United States, but probably not our over-massiveness problem.

And fly off into space!!!!!


Carla said...

That sure paints an interesting picture.

If I'm standing on the equator, then, presumably I weigh more than when I'm standing on the North Pole. Would the difference be big enough for a bathroom scale to pick up?

If so, maybe Canada's finally got an add campaign to bring people back from the tropics.

Kirk said...

Yeah, sorry, I reversed the way it goes. It is 9.81 m/s^2 at the North Pole (standard) and in a general sense decreases as you go down. I say "general sense" because in reality all sorts of things work in connection to change the perceived weight in different places.
It was a misunderstanding of what my professor said, which he clarified today.

Nathan said...

So, and correct me if I'm wrong, another way to lose weight would be to run eastward, increasing speed by running in the same direction as the earth's rotation. Is this so? And, if so, do you plan to become a multi-millionaire by writing a weight-loss book about it?

Homemanager said...

Ha!Can I join your weight-loss program? If I was running like Nathan is suggesting than it wouldn't matter too much where I'm standing (running) I would lose weight because I'm exercising! :-D