Depth 2 · 35 s
Sixty here, ten there
An astronaut's bathroom scale says 60 kg at home and 10 kg on the Moon, but she is made of exactly the same stuff - her mass hasn't changed. The scale feels how hard she is pulled, her weight, and the Moon pulls about a sixth as hard. A balance compares masses, so it gives the same answer anywhere.
About this video
An astronaut steps on a bathroom scale at home and it reads 60 kg. On the Moon, the same scale under the same astronaut reads 10 kg. Has she lost 50 kilograms? No. She is made of exactly the same stuff, so her mass hasn't changed at all.
What changed is the pull of gravity. The Moon pulls about a sixth as hard as the Earth, and how hard you are pulled is your weight. A bathroom scale feels weight and shows it as kilograms, so on the Moon it is fooled. A balance works differently: it compares one mass with another, and both pans are pulled alike, so it stays level on the Earth, on the Moon or anywhere else. This animation shows the difference between mass and weight: weight changes from place to place, but your mass goes with you.
This video shows depth 2 of Mass.
Learn MassTranscript
- 0:00On Earth the scale says 60 kilos. On the Moon, just 10.
- 0:04An astronaut stands on a bathroom scale at home: 60 kilograms.
- 0:09Same scale, same astronaut, on the Moon: 10.
- 0:13She hasn't lost anything. Same stuff, same mass.
- 0:17What changed is the pull: the Moon's is about a sixth.
- 0:22That pull is weight. A bathroom scale feels weight, so it's fooled.
- 0:26A balance compares masses, so it reads the same anywhere.
- 0:30Weight changes. Mass goes with you.