Ever wonder what the easiest way to lose weight is? Here's the one simple trick you need. Go to the equator. There, the planet is trying to throw you into space so much that you weigh less than you do anywhere else.
If you need confirmation that you are on a big, whirling space rock here's a simple way to do it. Get a really good scale, fly both it and yourself to the equator, and weigh yourself. You'll have lost a little weight.
You only have weight because gravity is pulling you towards the center of the Earth. At the poles, gravity is working alone - and it works best alone. The planet is spinning, but the ground directly beneath you (assuming you stand on one toe right at the pole) will essentially be still. Step away from the pole, and you will be traveling in a little circle, pushed all the time by the motion of the Earth. At the equator, that circle isn't so small, and the planet is doing its damnedest to throw you into space. If you've ever tied a string around a rock and whirled it in a circle, you know how it will move if you let go. By holding on to the string you are imparting some centripetal acceleration to the rock. At the poles, the 9.8 meters per second per second gravitational acceleration go entirely towards pushing down on a scale. At the equator, some of it is transformed into centripetal acceleration, counteracting your tendency to fly into space and holding you to Earth. How much? Let's find out.
Centripetal acceleration is the velocity of an object squared, divided by the radius of the circle it is moving around. The circumference of the Earth at the equator is 40,075 kilometers. Divide that by the number of seconds in a day, and we have a velocity of 0.4638 kilometers per second. Square that and divide it by the 6400 kilometer radius of the Earth, and we get an acceleration of 0.03 meters per second per second. Not much, but enough to drop your weight down.
But there's a complication. You aren't just heavier at the poles because you're not being hurled into space by an angry planet The world isn't a perfect sphere. Its spin causes it to be wide in the middle, and squished down at the poles. You are closer to the center of the Earth when you're at the poles, and so weigh even more. Based on acceleration alone, you weigh about 0.3 percent less at the equator. Factor in that extra-strong gravity at the poles, and you are about 0.5 percent heavier at the poles than at the equator.
Scale Image: National Human Genome Research Institute
Earth Image: NASA