Weight is a bit of a mind-bender. I had always thought of my weight, on any given day, as a constant, a physical trait like my height or my eye color. It’s not. I weigh 127 pounds on Earth, but on the much smaller moon, whose gravitational pull is one sixth of Earth’s, I weigh about as much as a beagle. Neither weight is my real weight. There is no such thing as a real weight, only real mass. Weight is determined by gravity. It’s a measure of how fast you’ll accelerate if you happen to be dropping through the air like Newton’s apple.
