05. How much does the Moon weigh? (A K2S Question)
From The Space Library
Things can only have weight in a gravity field, like on the Earth or on the Moon. The Moon is in the gravitational sphere of influence of the Earth (which is why it is in orbit), but it has its own gravitational sphere of influence as well, and can be thought of as being in free fall around the Earth, just like astronauts in the Shuttle or on the Space Station. Things have mass all the time because mass is the amount of matter we are made up of. Weight, then, is the pull of gravity on that mass at the planet's surface—like when you're standing on a scale—but can be a function of other forces as well, such as in a roller coaster ride. On Earth my mass weight is 176 pounds. In space my mass would be effectively weight-less, and on the Moon my mass would weigh around 31 pounds. On Mars I would weigh 66 pounds—same amount of mass for me, but with different gravitational pulls, depending on the mass of the attracting body. Since Earth surface normally is considered one gravity (g), then technically, when I say in conversation that I weigh 176 pounds, what I mean is 176 pounds per one-g. One very important thing to remember in space is that inertia is a function of mass, not weight. Changing direction while walking on the Moon is a bit more difficult than on Earth, as you don't have as much traction with the ground to force a change in your velocity vector. Remember that when you go running down the moonbase corridors! The Moon's mass, or amount of matter, is much smaller than Earth's, and is calculated at 8.10 x 1019 tons. Its mass in tons would be written out as 810 followed by 17 zeroes. Earth is about 81 times that massive. The Moon's density (mass divided by volume) is about 208 pounds per cubic foot, roughly 60 percent of Earth's density. Comparing the mass of the Moon with the mass of the Earth shows how much less massive the Moon is. Remember, a ton is 2,000 pounds. Mass of: pounds Moon 162,000,000,000,000,000,000,000 Earth 13,179,920,000,000,000,000,000,000
Answer provided by Thomas Matula, Ph.D. & Kenneth J. Murphy
Question and Answer extracted from the book Kids to Space - by Lonnie Schorer
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