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How Much Does the Moon Weigh?

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How much does the moon weigh?

C Stuart Hardwick:

Nothing.

Okay, I’m being a bit pedantic. The mass of the moon, which might be what you mean to ask, is approximately 7.3476× 10^22 kilograms.

But the moon doesn’t weigh anything.

Weight is directly related to mass, but it’s not the same thing as mass (even through we call units of weight and mass by the same names). Weight is the force exerted by gravity against a body resting against a larger mass. The moon is in freefall—in orbit—so it doesn’t weigh anything. If it were placed on the surface of the Earth, it would weigh about 7.3476 × 10^22 kilograms—but only for a moment. Then it would collapse under its own weight and become a rather disastrous pimple on the Earth until it broke through the crust.

That would be a bad day.

But fortunately, there is no realistic way that could ever happen. The moon is in orbit, which means it’s falling toward Earth (which is why it doesn’t “feel” our gravity—it’s weightless), but it’s also coasting away into space such that for every meter it falls toward us, it moves far enough for Earth’s surface to curve away one meter. Therefore, like any orbiting body, it goes round and round and round.

This weight versus mass thing confuses a lot of folks because in colloquial English we use pounds and kilograms for both measurements of weight and mass. That is because we figured all this stuff out on Earth, where it was simple and practical to measure mass by measuring weight.

In other words, because we are earthlings, we define units of mass as equal to the observed units of weight as measured on Earth.

If you like science, you might like my free, award-winning sci-fi sampler.

This post originally appeared on Quora. Click here to view.

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Big Questions
Why Does Turkey Make You Tired?
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Why do people have such a hard time staying awake after Thanksgiving dinner? Most people blame tryptophan, but that's not really the main culprit. And what is tryptophan, anyway?

Tryptophan is an amino acid that the body uses in the processes of making vitamin B3 and serotonin, a neurotransmitter that helps regulate sleep. It can't be produced by our bodies, so we need to get it through our diet. From which foods, exactly? Turkey, of course, but also other meats, chocolate, bananas, mangoes, dairy products, eggs, chickpeas, peanuts, and a slew of other foods. Some of these foods, like cheddar cheese, have more tryptophan per gram than turkey. Tryptophan doesn't have much of an impact unless it's taken on an empty stomach and in an amount larger than what we're getting from our drumstick. So why does turkey get the rap as a one-way ticket to a nap?

The urge to snooze is more the fault of the average Thanksgiving meal and all the food and booze that go with it. Here are a few things that play into the nap factor:

Fats: That turkey skin is delicious, but fats take a lot of energy to digest, so the body redirects blood to the digestive system. Reduced blood flow in the rest of the body means reduced energy.

Alcohol: What Homer Simpson called the cause of—and solution to—all of life's problems is also a central nervous system depressant.

Overeating: Same deal as fats. It takes a lot of energy to digest a big feast (the average Thanksgiving meal contains 3000 calories and 229 grams of fat), so blood is sent to the digestive process system, leaving the brain a little tired.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Big Questions
How Are Balloons Chosen for the Macy's Thanksgiving Day Parade?
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The balloons for this year's Macy’s Thanksgiving Day Parade range from the classics like Charlie Brown to more modern characters who have debuted in the past few years, including The Elf On The Shelf. New to the parade this year are Olaf from Disney's Frozen and Chase from Paw Patrol. But how does the retail giant choose which characters will appear in the lineup?

Balloon characters are chosen in different ways. For example, in 2011, Macy’s requested B. Boy after parade organizers saw the Tim Burton retrospective at the Museum of Modern Art. (The company had been adding a series of art balloons to the parade lineup since 2005, which it called the Blue Sky Gallery.) When it comes to commercial balloons, though, it appears to be all about the Benjamins.

First-time balloons cost at least $190,000—this covers admission into the parade and the cost of balloon construction. After the initial year, companies can expect to pay Macy’s about $90,000 to get a character into the parade lineup. If you consider that the balloons are out for only an hour or so, that’s about $1500 a minute.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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