Why doesn't ground cave in?\nthe ground never collapses?
406328
Okay listen carefully,\n\nOil is not found in caves for Heaven's sake! Oil is found inside porous permeable rocks. That means that tiny holes are interconnected together like a network of capillaries. When you pump out the oil there is no real big void left to cave in. Besides water is sometimes found w/ the oil. Since oil is less dense it rides over the top of the water. So if anything fills the spaces left behind it will be water!\n\nNow the ground will cave in where they pump massive amounts of groundwater out of aquifers found in limestone bedrock.\n\nLimestone dissolves due to natural acids such as carbonic acid. Voids or caverns or caves, whichever you prefer to call them are created & fill w/ water. When the water is pumped out, there is nothing left to support the structures above. The ground caves in & poof you have a sinkhole.\n\nSinkholes have been known to swallow whole blocks in cities. Florida is entirely underlain w/ limestone bedrock. The whole state has sinkholes everywhere.\n\nSo don't be concerned about pumping oil out & leaving gaping holes behind. Those you don't have to worry about. You do have to worry about pumping too much groundwater.\n\nTurn off the water while you are brushing your teeth next time.
931890
You just got your basic wrong. Try to reveal them again, and understand the ground physics first...\n\nThis webpage may help you to have preliminary understanding...\n\nhttp://computer.howstuffworks.com/hard-disk.htm
667234
I will be damned if I know, lol, but, I am about to- but hope to never need to use one:)\n\nParachutes work because of something called ‘air resistance.’ If there were no air resistance, then gravity would cause everything to fall at the same rate, so no matter what item you dropped (i.e. a feather or a rock), it would hit the ground at exactly the same time (assuming you dropped it from the same height). But air resistance complicates things (and makes sky-diving a lot more fun). Air resistance happens because as things fall, they have to push their way past the atoms and molecules that make up air in order to get where they’re going.\n\nFor something like a rock, this isn’t really a big deal, since rocks tend to be really heavy while being pretty small, so they can push the air molecules out of the way quite easily. But things like feathers can’t push the air molecules out of the way very well – for one, they weigh less so they don’t push as hard. And for another, they’re pretty big, so they run into a lot more air molecules than the rock does. So the air actually slows the feather down.\n\nThis is what makes parachute work. If a person were to fall without a parachute, they’d push the air molecules out of the way very easily, so the air wouldn’t be able to do much to slow the person down. But if the person is attached to a parachute, then the parachute will run into lots of air molecules, and especially if it’s curved to be higher up in the middle, it will be very hard for the air molecules to get out of the way. If they can’t get out of the way, they will slow the parachute (and hence the person) down. \n\nAnother way to put it:)\n\n    *  A parachute works to slow down someone or something from falling by creating “drag”.\n    * Drag is the push on something from air or water.\n    * Because air is much thinner than water it doesn’t have as much drag.\n    * The bigger something is – the larger it’s surface area the more drag it creates.\n    * That’s why a parachute works so well – it’s very light and it has a very big surface area. It catches lots of air in it as it falls so it creates lots of drag which slows it down as it falls. \n\nHope you are happy now, I am still NOT jumping out of an airplane, lol
955624
If it wasn't for gravity, there would be no earth.  (Gravity holds the earth together.)  \n\nThe very notion of "up" and "down" *needs* gravity, or it has no meaning.  The very notion of "down" has always meant,  "in the direction of gravity", even before we knew what gravity was.  If you are in a room with no windows, how do you know which way is "down"?  Because "down" is THE DIRECTION THAT THINGS FALL.  When you stand up, it's THE DIRECTION OF YOUR FEET.  Without gravity, there is no notion of falling, and no notion of "standing up" so "down" (and "up") have no meaning.  Think of astronauts in a room with no windows on the Space Station.  They have no "up" or "down". \n\nOr think of it another way.  The notion of "up" and "down" has less to do with the direction of the earth, as with the direction of gravity.  If you are standing on the moon, or on mars, which way is "down"?  It will be in the direction things fall ... towards the planet you are standing on.  So "down" is defined relative to the current direction of gravity, regardless of what is causing that gravity.\n\nSo the earth has no "up" and "down" except with respect to gravity.  It also has no "top" or "bottom" ... the North Pole is not the top of the earth.  We just like to make maps that way, but there's no scientific reason for it.    (The Egyptions drew maps relative to the Nile river ... so the "upper Nile" is South, and the "lower Nile" is North.)
212531
Finally a way for me to pick up that 7-10 split!  :)\n\nI agree with the basic premise of oscillating assuming a vacuum (since we are assuming no molten core, why not a vacuum as well?).\n\nBut, depending on the direction of the hole in relationship to the rotational axis of the earth, wouldn't the ball start bouncing against the sides of the hole due to the mechanics similar to that of a Foucault Pendulum?
855104
so that the manhole cover won't fall into the manhole. if it was square, then it could fall into the hole when placed diagonally. same goes for any other shape.
210848
Ignore Zelo's first parahgraph, he is pulling your leg.\nHis second paragraph is correct though. However, the difference in gravity between Denver and Orlando is barley measurable. I can provide calculations in anyone is interested in the details. \n\nOnto your main question. The air pressure inside is exactly the same indoors as it is outside. Houses and buildings are not perfectly sealed like a bicycle tire or light bulb is. Open doors/ windows and small leaks all over keep the pressure the same inside as it is outside, which is a good thing. If the  air pressure inside were much lower we couldn't breath or function normally. If it got to low too fast you would just plain explode! Don't worry though, the pressure on the ground simply can't get that low.\n\nAs far as pressure affecting your weight: It is true that the air pressure pushes down on your shoulders, but it also lifts up on your arm pits. Remember pressure is everywhere on you body in every direction. In the end all of those ups and downs cancel each other out, leaving only gravity to affect your weight. \n\nOddly enough, in  very very small way the air actually lifts you up a tiny tiny bit in the same way that a heavy object in a swimming pool is lighter when it is in the water. You are slightly, not an amount you could easily measure, lighter in the atmospher than you would be if there were no atmosphere at all.   \n\nThis and a few other reasons are why, in science, mass is used instead of weight. Mass is always the same while weight can be affected by outside things. \n\nThese are great questions, keep pondering and asking.
1056060
Caves form in limestone rock. I believe you are asking about the process. So here it goes...\n\nAs water moves through the ground it becomes slightly acidic due to the decomposition of organic material. The acid formed is a mild carbonic acid.\n\nAs this mildly acidic water reaches the rock it permeates the cracks and crevices. Over time, the acid reacts w/ the limestone (calcium carbonate - CaCO3) & dissolves it.\n\nThe cracks get larger. Over long periods of time these cracks can get extremely large resulting in a cave.\n\nIf a cave gets large enough it will be considered a cavern.\n\nSometimes a cavern will collapse due to the weight of the overlying material. When this happens a sinkhole occurs.\n\nSinkholes can be small or large depending upon the size of the cavern beneath & the area of structural weakness.\n\nSometimes a cavern collapses b/c groundwater is pumped out for local supplies. When this happens, there is no support left holding up the roof of the cavern & it gives way.\n\nFlorida is notorious for the number of sinkholes that occurs there. Of course, Florida has limestone bedrock underlying the entire state so this is bound to happen on a regular basis. Also, Florida's population is growing & so is their need for water.\n\nKarst topography is the term given to areas that are dominated by limestone landforms that were created from dissolution by acidic groundwater.
858875
First off, much of the interior of the earth is molten after you get about 30K down, so you couldn't really drill a hole through it. But for arguments sake, let's say you built a super-strong tube out of some nano-material and inserted it through the center of the Earth from pole to pole. Now you drop your stone.\n\nThe stone would fall towards the center of gravity, the center of the Earth. It would accelerate as it fell, so it would presumably fall past the center and head towards the South Pole. As it headed towards the South Pole, the gravitation pull would slow it down. Would it manage to to escape the Earth's gravity? No.\n\nConsider that the stone being at the top of the North Pole represents "potential kinetic energy". You could have generated energy from its fall much like a dam creates energy from falling water. Instead, it fell freely towards the center of the Earth, and all its potential kinetic energy has been turned into velocity. That velocity can't be enough to go any further than it fell (that is, out of the South Pole) because where would the excess energy come from?\n\nNow when the stone is at the center of the Earth, it has no potential kinetic energy. It can't fall anywhere, because every direction is up. All of its potential kinetic energy has been turned into velocity and so it should "fall up" the distance that it fell down. When it reaches the South Pole, it will have no velocity left, but it will have the same potential kinetic energy as when it started to fall. So you might expect it to fall from pole to pole indefinitely.\n\nHowever, if the tube is full of air, we have a problem. Falling objects normally have a "terminal velocity", which is the speed at which the air resistance stops the object from accelerating further. The air pressure at the center of the Earth would be enormous (air would probably be a liquid at these pressures and temperatures), as it would be subject to the weight of the air both north and south of the hole pulled in towards the center. The increasing density of air would slow the object as it fell to where it had little momentum as it approached the center. It might overshoot somewhat, but friction would continue to slow it until it was drawn to the center of gravity.\n\nNow if the tube contained a perfect vaccuum, the object should continue to fall from pole to pole indefinitely...except there's the problem that the stone would hit the sides of the hole due to the rotation of the Earth. See Foucault's Pendulum. This would slow it down, causing it again to settle at the center of the Earth.\n\nThere you have it. No need to drill through the center of the Earth now.
623233
It's gravity that keeps everything in place. And ya'll, don't be hatin' on this persn, it's just a question!
528890
depends on your perspective doesn't it.\n\nbut by definition, "down" is in the direction of gravity.\n\nit is impossible to dig "up" unless you were underground.
1051553
By never-ending it implies that there is no bottom, so you would simply continue to fall for all eternity.  No bottom, no splat, therefore no place to end up.
845607
I'v heard about buildings being put on ball bearings so that the building will remain stable while the earth rocks beneith it. I'v seen a few specials on the Discovery Channel about it. Apparently the technology was pioneered in Japan. It makes sense since Japan has A LOT of earthquakes.
1117618
when its ready it just has to go somewhere. It takes the path of least resistance trying to equalize its energy. It usually goes to ground.
618210
Not due to gravitational pull?!
358151
simple, because it can never fall in,no matter how you move it
463808
In order to combat gravity, we would need to be able to understand what it is. At the moment, we don't. If we did, it still would be a tall order to mess with the field of a whole planet. Assuming we could "stabilize" gravity at the quantum level, whatever device we invented to do this would undoubtedly require huge amounts of energy.\n\nA much easier method would be to install a system of shock absorbers and hydraulics underneath the floor. Controlled by a computer, these could make up for some weakenings in the field and simulate to the human feet an equal field. This wouldn't actually solve the problem, just treat the syptoms. The air pressure of the cabin could also be increased to press our feet down on the ground more, but if we mess with this too much, we will implode. Also, there is the idea of placing a large verticaly aligned doughnut-shaped cabin to produce "gravity" in the form of centrifugal force, but this would be extremely impractical and require a lot of digging. I hope this helps, because until we have Artificial Gravity, there isn't really a lot that can be done. Cool question, though.