How Much Does the Moon Weigh?

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iStock

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.

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

What's the Difference Between Straw and Hay?

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iStock.com/dusipuffi

The words straw and hay are often used interchangeably, and it's easy to see why: They're both dry, grassy, and easy to find on farms in the fall. But the two terms actual describe different materials, and once you know what to look for, it's easy to tell the difference between them.

Hay refers to grasses and some legumes such as alfalfa that are grown for use as animal feed. The full plant is harvested—including the heads, leaves, and stems—dried, and typically stored in bales. Hay is what livestock like cattle eat when there isn't enough pasture to go around, or when the weather gets too cold for them to graze. The baled hay most non-farmers are familiar with is dry and yellow, but high-quality hay has more of a greenish hue.

The biggest difference between straw and hay is that straw is the byproduct of crops, not the crop itself. When a plant, such as wheat or barley, has been stripped of its seeds or grains, the stalk is sometimes saved and dried to make straw. This part of the plant is lacking in nutrients, which means it doesn't make great animal fodder. But farmers have found other uses for the material throughout history: It what's used to weave baskets, thatch roofs, and stuff mattresses.

Today, straw is commonly used to decorate pumpkin-picking farms. It's easy to identify (if it's being used in a way that would be wasteful if it were food, chances are it's straw), but even the farms themselves can confuse the two terms. Every hayride you've ever taken, for example, was most likely a straw-ride.

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How and Why Did Silent Letters Emerge in English?

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iStock/Bychykhin_Olexandr

Kory Stamper:

The easy answer is “"because English can’t leave well enough alone."

When we first started speaking English around 600 AD, it was totally phonetic: every letter had a sound, and we sounded every letter in a word. But English—and England itself—were influenced quite a bit by the French, who conquered the island in 1066 and held it for a long time. And then later by Dutch and Flemish printers, who were basically the main publishers in England for a solid two centuries, and then by further trading contact with just about every continent on the planet. And while we’re shaking hands and stealing language from every single people-group we meet, different parts of the language started changing at uneven rates.

By the 1400s, English started to lose its phonetic-ness: the way we articulated vowels in words like “loud” changed slowly but dramatically, and that had an effect on the rest of the word. (This is called “The Great Vowel Shift,” and it took place over a few hundred years.) Somewhere in the middle of the GVS, though, English spelling became fixed primarily because of the printing press and the easy distribution/availability of printed materials. In short: we have silent letters because the spelling of words stopped changing to match their pronunciations.

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

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