Earth's Gravity
When I was a kid, I thought that Earth’s gravity was caused by its spinning molten core, like an electric magnet spinning to generate gravity. The real answer is gravity is caused by the MASS of an object; the larger the mass of the object, the greater the force of its gravity. Even we humans have our own gravity fields!
More info:
Quickie Questions – Extraordinary Earth – Gravity/Magnetism
Really cool additional info on new discoveries in gravity as well as quantum physics:
http://www.pbs.org/wgbh/nova/elegant/program.html
What exactly is the mass of an object? Mass is sometimes mistaken for the weight of an object (and sometimes mass is the same as the weight of an object), but here’s the real answer:
http://en.wikipedia.org/wiki/Mass