It amazes me that the earth rotates at exactly the same speed every single day and has done so for a long time. How can I understand bett…

Answer by HM Wamboldt:

Ah. But the Earth doesn't rotate at the same speed every day. Ask any astronomer. They periodically have to adjust the computers which point their largest telescopes to accommodate the Earth rotating slower or faster.

Source: International Earth Rotation and Reference Systems Service

The change is very very small, but it's measurable and affects the length of the day. It's caused by rainy seasons filling high altitude lakes like Lake Mead and the Yangtze River behind the Three Gorges Dam. Lakes and their watersheds around the globe are filled during the rainy season, this slows the Earth's rotation. The Earth then speeds up as the water drains into the oceans as the year progresses. Since most of these areas are in the northern hemisphere, there is an imbalance between the northern hemisphere's rainy season and the southern hemisphere's rainy season. The result is an annual speeding up and slowing down of the Earth's rotation.

As glaciers melt into the oceans the Earth speeds up.

When plate tectonics lift mountains the Earth slows down. When parts of the crust drop along rift valleys the Earth speeds up.

When the average global winds blows harder from the West to the East the Earth's rotation slows down. When the average global winds blows harder from the East to the West the Earth's rotation speeds up.

As for why planets don't just slow down and stop, yes, you answered your own question. It's because it's spinning in a vacuum, and since it's in a vacuum there is no friction to slow it down.

Kinda cool,
Best Rgds,
-H-

It amazes me that the earth rotates at exactly the same speed every single day and has done so for a long time. How can I understand bett…

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Why do watermelons have so many seeds?

Answer by Robert Frost:

The idea behind seeds is that animals will come along and eat the fruit, wander off somewhere, and then poop out the seeds which will grow into the next generation of plants.

There's a lot of risk there.  What happens if the animal chews up the seeds?  What happens if the animal poops in a unsuitable location?  What happens if the animal falls in a river and gets carried out to sea?  The seeds will be lost.

To account for these flaws in the otherwise brilliant plan, plants evolved to have more seeds – meaning the plants that produced more seeds were more likely to get at least one seed successfully planted.

More seeds means a greater chance of a next generation.  But producing seeds costs energy.  It has to be moderated.  If watermelons have evolved to have two hundred seeds, it must mean that there is an advantage to having two hundred seeds – an advantage worth the energy cost.

At this point you're probably thinking "yeah, fine that makes sense.  But, still, why so many?  I had an apple yesterday and it had about ten seeds in it.  This watermelon has about two hundred!!"

Yes, but that apple tree had about sixty apples on it.  So, that means a total of about 600 seeds to disperse.  How many watermelon grow on a vine?  Maybe three.  There's your same 600 seeds.

Why do watermelons have so many seeds?