Note that as you fell, you accelerate all the way down, but the acceleration itself would decrease a

Good advice from the 70s progressive band. Look around you. Unless you re one of the Apollo astronauts, you ve lived your entire life within a few hundred kilometers of the surface of the Earth. There s a whole planet beneath your feet, 6.6 sextillion aaa car rentals tons of it, one trillion cubic kilometers of it. But how well do you know it?
Below are ten facts about the Earth the second in my series aaa car rentals of Ten Things You Don t Know (the first was on the Milky Way ). Some things aaa car rentals I already knew (and probably you do, too), some I had ideas about and had to do some research to check, and others I totally made up. Wait! No! Kidding. They re all real. But how many of them do you know? Be honest.
Maybe you ve heard this statement: if the Earth were shrunk down to the size of a billiard ball, it would actually be smoother than one. When I was in third grade, my teacher said basketball, but it s the same concept. But is it true? Let s see. Strap in, there s a wee bit of math (like, a really wee bit).
OK, first, how smooth is a billiard ball? According to the World Pool-Billiard Association , a pool ball is 2.25 inches in diameter, and has a tolerance of +/- 0.005 inches. In other words, it must have no pits or bumps more than 0.005 inches in height. That s pretty smooth. The ratio of the size of an allowable bump to the size of the ball is 0.005/2.25 = about 0.002.
aaa car rentals The Earth has a diameter of about 12,735 kilometers (on average, see below for more on this). Using the smoothness ratio from above, the Earth would be an acceptable pool ball if it had no bumps (mountains) aaa car rentals or pits (trenches) more than 12,735 km x 0.00222 = about 28 km in size.
But it s not a perfect sphere. It spins, and because it spins, it bulges due to centrifugal force (yes, dagnappit, I said centrifugal aaa car rentals ). That is an outwards-directed force, the same thing that makes you lean to the right when turning left in a car. Since the Earth spins, there is a force outward that is a maximum at the Earth s equator, making our Blue Marble bulge out, like a basketball with a guy sitting on it. This type of shape is called an oblate spheroid .
If you measure between the north and south poles, the Earth s diameter aaa car rentals is 12,713.6 km. If you measure across the Equator it s 12,756.2 km, a difference of about 42.6 kilometers. Uh-oh! That s more than our tolerance for a billiard ball. So the Earth is smooth enough, but not round enough, to qualify as a billiard ball.
But we re not done. The Earth is more complicated than an oblate spheroid. The Moon is out there too, and the Sun. They have gravity, and pull on us. The details are complicated ( sate yourself aaa car rentals here ), but gravity (in the form of tides) raises bulges in the Earth s surface as well. The tides from the Moon have an amplitude (height) of roughly a meter in the water, and maybe 30 cm in the solid Earth. The Sun is more massive than the Moon, but much farther away, and so its tides are only about half as high.
Other forces are at work as well, including pressure caused by the weight of the continents, upheaval due to tectonic forces, aaa car rentals and so on. The Earth is actually a bit of a lumpy mess, but if you were to say it s a sphere, you d be pretty close. If you held the billiard-ball-sized Earth in your hand, I doubt you d notice it isn t a perfect sphere.
If the Earth were infinitely elastic, then it would respond freely to all these different aaa car rentals forces, and take on a weird, distorted shape called a geoid . For example, if the Earth s surface were completely deluged with water (give it a few decades) then the surface shape would be a geoid. But the continents are not infinitely ductile, so the Earth s surface is only approximately a geoid. It s pretty close, though.
Precise measurements of the Earth s surface are calibrated against this geoid, aaa car rentals but the geoid itself is hard to measure. The best we can do right now is to model it using complicated mathematical functions. That s why ESA is launching a satellite called GOCE (Gravity field and steady-state Ocean Circulation Explorer) in the next few months, to directly determine the geoid s shape.
I grew up thinking that if you dug a hole through the Earth (for those in the US) you d wind up in China. Turns out that s not true; in fact note that the US and China are both entirely in the northern hemisphere which makes it impossible, so as a kid I guess I was pretty stupid.
Well, you d die (see below). But if you had some magic material coating the walls of your 13,000 km deep well, you d have quite a trip. You d accelerate all the way down to the center, taking about 20 minutes to get there . Then, when you passed the center, you d start falling up for another 20 minutes, slowing the whole way. You d just reach the surface, then you d fall again. Assuming you evacuated the air and compensated for Coriolis forces, you d repeat the trip over and over again, much to your enjoyment and/or terror. Actually, this would go on forever, with you bouncing up and down. I hope you remember to pack a lunch.
Note that as you fell, you accelerate all the way down, but the acceleration itself would decrease as you fell: there is less mass between you and the center of the Earth as you head down, so the acceleration due to gravity decreases as you approach the center. However, the speed with which you pass the center is considerable: about 7.7 km/sec (5 miles/second).
In fact, the math driving your motion is the same as for an orbiting object. It takes the same amount of time to fall all the way through the Earth and back as it does to orbit it, if your orbit were right at the Earth s surface (orbits slow down as the orbital radius increases). aaa car rentals Even weirder, it doesn t matter where your hole goes: a straight line through the Earth from any point to any other (shallow chord, through the diameter, or whatever) gives you the same travel time of 42 or so minutes .
A long time ago, you, me, and everything else on Earth was scattered in a disk around the Sun several aaa car rentals billion kilometers across. Over time, this aggregated into tiny bodies called planetesimals , like dinky asteroids. These would smack together, and some would stick, forming a larger body. Eventually, this object got massive enough that its gravity actively drew in more bodies. As these impacted, they released their energy of motion (kinetic energy) as heat, and the young Earth became a molten ball. Ding! One source of heat.
Since the Earth was mostly liquid, heavy stuff fell to the center and lighter stuff rose to the top. So the core of the Earth has lots of iron, nickel, osmium, and the like. As this stuff falls, aaa car rentals heat is generated (ding ding ding!) because the potential energy is converted to kinetic energy, which in turn is converted to thermal energy due to friction.
So the Earth is hot in the inside due to at least four sources. But it s still hot after all this time because the crust is a decent insulator. It prevents the heat from escaping efficiently, so even after 4.55 billion years, the Earth s interior is still an unpleasantly warm place to be.
Incidentally, the amount of heat flowing out from the Earth s surface due to internal sources is about 45 trillion Watts. That s about three times the total global human energy consumption. If we could capture all that heat and convert aaa car rentals it with 100% efficiency into electricity, it would literally power all of humanity. Too bad that s an insurmountable if.
Most people think the Earth has one natural moon, which is why we call it the Moon. These people are right. But there are four other objects at least that stick near the Earth in the solar system. They re not really moons, but they re cool.
The biggest is called Cruithne ( pronounced MRPH-mmmph-glug, or something similar). It s about 5 kilometers across, and has an elliptical orbit that takes it inside and outside Earth s solar orbit. The orbital period of Cruithne is about the same as the Earth s, and due to the peculiarities of orbits, this means it is always on the same side of the Sun we are. From our perspective, aaa car rentals it makes a weird bean-shaped orbit, sometimes closer, sometimes farther from the Earth, but never really far away.
Sure, we re safe from Cruithne. But space is littered with detritus, and the Earth cuts a wide path (125 million aaa car rentals square km in area, actually). As we plow through this material, we accumulate on average 20-40 tons of it per day! [Note: your mileage may vary; this number is difficult to determine, but it's probably good within a factor of 2 or so.] Most of it is in the form of teeny dust particles which burn up in our atmosphere, what we call meteors (or shooting stars, but doesn t meteor sound more sciencey?). These eventually fall to the ground (generally transported by rain drops ) and pile up. They probably mostly wash down streams and rivers and then go into the oceans.
40 tons per day may sound like a lot, but it s only 0.0000000000000000006% the mass of the Earth (in case I miscounted zeroes, that s 2 10 -26 6 10 -21 times the Earth s mass). It would take 140,000 million 450,000 trillion years to double the mass of the Earth this way, so again, you might want to pack a lunch. aaa car rentals In a year, it s enough cosmic junk to fill a six-story office building, if that s a more palatable analogy.
I ll note the Earth is losing mass, too: the atmosphere is leaking away due to a number of different processes. But this is far slower than the rate of mass accumulation, so the net affect is a gain of mass.
The height of a mountain may have an actual definition, but I think it s fair to say that it should be measured from the base to the apex. Mt. Everest aaa car rentals stretches 8850 meters above sea level, but it has a head start due to the general aaa car rentals uplift from the Himalayas. The Hawaiian volcano Mauna Kea is 10,314 meters from stem to stern (um, OK, bad word usagement, but you get my point), so even though it only reaches to 4205 meters above sea level, it s a bigger mountain than Everest.
aaa car rentals Considering I wrote a book about destroying aaa car rentals the Earth a dozen differe