And You Thought Gravity Just Pulled You Down?
Gravity... it's something you don't put a lot of thought into most of the time. It's what pulls you straight down, right? Wrong. If you remember from your basic high school physics, gravity is the attraction between two objects. The amount of gravity is directly proportional to the mass of an object. The Sun's gravity is what keeps the Earth from flying out into space as it orbits at 67,000 miles per hour. The Earth's gravity is what keeps the moon in orbit. And the Earth's gravity is what pulls you down toward the ground... what most people don't think about is that space is not the only place where gravity varies. The mass of an object determines it's gravitational force. The mass of, say, a mountain range pulls you toward it. The image at left is from Discover magazine's article Grace in Space. It is a map of the gravitational measurements that two 'Grace' satellites have taken of Earth. It shows the gravitational fluctuations of matter on Earth. For example, mountain ranges have their own gravitational pull, and they can actually see the variations over time of water tables. When there is a lot of water present in a land mass, it has more gravity than when it's not present, for example. So when you see someone scaling the side of a mountain, remember, gravity is actually helping to pull them toward the mountain a little bit, not just toward the ground.