When we say that a person weighs 75 kilograms (165 pounds), we are referring to that personÕs weight on Earth. This weight is a result of the EarthÕs gravitational pull acting on that personÕs actual mass. Mass is the amount of matter that something contains. If we were to take that 75 kilogram (165 lb.) person into space, her or his weight would change. Without any noticeable gravity acting on that person, he or she would weigh practically nothing at all. However, that personÕs mass would remain exactly the same.