StartsWithABang writes: Imagine you wanted to know what your acceleration was anywhere on Earth; imagine that simply saying “9.81 m/s^2" wasn’t good enough. What would you need to account for? Sure, there are the obvious things: the Earth’s rotation and its various altitudes and different points. Surely, the farther away you are from Earth’s center, the less your acceleration’s going to be. But what might come as a surprise is that if you went up to the peak of the highest mountains, not only would the acceleration due to gravity be its lowest, but there’d also be less mass beneath your feet than at any other location.