G, the symbol for gravity, is the most necessary of forces. It's the force that allows us to react when someone tells us to "get down" in a shoot-out. It's what would, in a vacuum, blow our minds by causing a bowling ball and feather to fall at the same rate. It's the earthly power that keeps even the most airheaded of us pinned to the ground. And, it's what dropped fruit on the likes of Sir Isaac Newton as a way of announcing itself to the world. (Well, at least in legend.) Where would we be without gravity? We'd be 7 billion beings floating away from our comfy little homes and into outer space, soon to lose consciousness and the very breath of life a few minutes after. If that doesn't warrant a space in a top 10, certainly nothing does.