The gravity is the force of attraction between an object and the Earth or other celestial body. Prevents objects found on earth's surface ejection into space because of the speed of rotation of the celestial body. In the sixteenth century, Galileo Galilei discovered that in a vacuum all bodies fall at the same speed, regardless of their weight. In the seventeenth century, the Englishman Isaac Newton formulated a law that bears his name, according to which bodies attract with a force that depends on its mass, ie the amount of stuff they have. Because of this Earth, which has a much more massive than the Moon, has a more intense gravity that our natural satellite.
No, but they generally agree. But the bodies with the same mass may have a different weight, because it varies with changes in the intensity of the gravitational attraction at various points on Earth.
The average is 9 , 8 meters per second squared. But as the Earth is not a perfect sphere, but flattened at the poles, these are little more intense, and slightly lower in Ecuador.