Final answer:
When stepping on a scale, you are measuring the force of Earth's gravity on your mass, which is your weight. The scale converts this weight into a mass measurement in kilograms. Your mass does not change whether you are on Earth or the Moon, but your weight measurement would change due to different gravitational forces.
Step-by-step explanation:
When you step on a scale, you are measuring how strongly Earth's gravity is pulling down on you, which is your weight. This force is measured in newtons or pounds and is proportional to the amount of mass due to the presence of gravity. Bathroom scales contain springs that compress under your weight, and this compression is translated into a measurement of weight. Most scales provide this measurement and convert it to a mass reading in kilograms by dividing by the acceleration due to gravity (approximately 9.80 m/s2).
If you were to take the same scale to the moon and stand on it, the scale would not show the same mass as it does on Earth, as the gravitational pull on the moon is weaker than on Earth. Instead, it would show a lower weight due to the moon's lower gravity, but your mass would remain unchanged. Likewise, when standing on a scale in an elevator that is in free fall, such as when a cable snaps, the scale would read zero because there would be no normal force acting upon your body, not showing your real weight but rather indicating you are in a state of apparent weightlessness.