Why your mass stays the same
Move from Earth to the Moon and your body’s mass does not change. Mass describes how much matter makes up your body, and changing location does not remove or add that matter. What changes is your weight: the force gravity exerts on you.
A bathroom scale responds to that force. It measures how strongly you press against it, so in weaker gravity it gives a lower reading. On the Moon, for example, a person would weigh less than on Earth, even though the person’s mass is unchanged. The scale’s reading is not a direct measure of how much matter is in the person; it is a result of the gravitational pull acting on them.
Why astronauts float in orbit
Orbit does not mean gravity has vanished. A spacecraft and everything inside it are continuously falling toward Earth. Their forward motion carries them around the planet, so they keep missing the ground. Because the astronauts and the spacecraft fall together, neither is pressing normally against the other. That lack of support force is what produces the familiar feeling of weightlessness.
A scale aboard the spacecraft would not show an astronaut’s usual Earth weight, because the astronaut is not being held up against it in the ordinary way. But the astronaut has not lost mass. The distinction matters: weight depends on the gravitational force and support around you; mass remains a property of the matter you carry with you.
