I am assuming that the ground is firmly attached to the rest of planet earth (which is why I said standing on rock).
The ground in the US is travelling in the opposite direction to the ground in china so the ground could only go in a straight line in both locations in the planets disintegrates to dust. I am no physicist but gravity within a table tennis ball is negligable yet they don’t disintegrate as soon as a player apply spin to the ball. I believe the atoms of a solid are help together by atomic forces rather than gravity.
Friction doesn’t disappear when gravity disappears. That’s an even more terrifying thought experiment.
Yes houses are not reliant on gravity to keep themselves together. Have you seen those videos of floods and sinkholes where whole houses tumble over in (mostly) one piece? The floors, walls, roofs, and foundations are all tied together with nails, screws, straps, clips, anchor bolts, and rebar. The soil the house sits in is also bound together by friction and compressive forces. A ball of clay doesn’t disintegrate when it’s dug out of the ground after all.
Now, as the mass of the Earth starts pushing everything outwards due to momentum, that would seem to lead to a gradual flinging out of everything as an ever expanding disk of debris. However, that debris would (after however long it takes) be things like whole intact buildings, giant boulders, entire mountains in some cases, trees, people, cars, chunks of roads and bridges, all floating amongst globs of water, magma (lava?), loose soil, and random garbage.
Well, no, it wouldn’t disintegrate to dust. The pieces would probably be hundreds of meters across or more. Which wouldn’t be much comfort, because those pieces would fly apart, in a matter of minutes at most.
Centrapetal force is mass * velocity / radius. For an object on the equator than equates to 0.034 Newtons per kg of mass. That isn’t a lot but it would be enough for loose items to drift apart. The question I am not sure about is whether bedrock is a single piece over the whole planet (like a table tennis table), individual pieces held together by nothing but gravity or individual pieces held by something else.
A building will have foundations, if those foundations are vertical if gravity ended there will be a force of friction to prevent the building floating away but I do not know whether that would be stronger than the centrapetal force. A building is also likelty to have a series of other things connecting it to the ground for example pipes, an average house weighing 50 tonnes wil exert 1700N of centrapetal force I might be wrong but I would have thought all the pipes and wires etc connecting the house the the ground would be strong enough to resist that.
Regarding the planet itself I must admit I have no idea how strong the forces connecting the tectonic plates to each other are I had assumed the earth’s structural intregrity is strong enough to rotate once every 24 hours even if gravity is not keeing it together but I might be wrong.
[quote=“jjakucyk, post:22, topic:979607”]
The soil the house sits in is also bound together by friction and compressive forces.[/quote]
Soil is not going to hold your house down via friction. You also mention in your post that the soil is going to be flung into space. How does it hold your house down when it is also flung out into space. That was my whole point. The soil is going, too. Not just the house.
Also, what is causing the “compressive forces” you mention?
I never said the house falls apart. I said that both the house and the ground are flung out into space. The Earth itself doesn’t stay intact. Most houses are sitting in relatively loose soil. They aren’t bolted down to the bedrock, which itself is going to break apart anyway even if they were. The house and the ground are going to be flung out into space if the Earth lost its gravity.
A ball of clay is held together by the friction of the particles within it, surface tension of the moisture, non-chemical bonding between the various molecules, and in the upper layers, plant roots. None of that changes if gravity goes away. Coastal areas with a lot of sand are certainly looser than more interior areas with sand and loam, but even there the loosest stuff is mostly on the surface. A few feet underground and it’s much more consolidated and squeezed together. Same for bedrock. While layered limestone and shale will come apart into many small pieces, granite, marble, and other igneous and metamorphic rocks are going to maintain a lot of cohesion in the face of the relatively small forces at play in this scenario. I don’t know if that means we’re talking chunks of planet hundreds of feet or hundreds of miles in size, but “flung” into space suggests, in the colloquial sense, something much faster and more violent than the gradual floating apart described by previous posters.
Velocity is squared.
On planetary scales, there is no distinction.
Put it this way: Pick up a clump of dirt, holding onto it only by the top. For a small clump, you can do it, but for a larger clump, it’ll fall apart, because it gets too heavy for the relatively weak forces that hold clumps of dirt together.
Pick up a solid rock holding it only by the top. The forces holding together a solid rock are stronger than those holding together a clump of dirt, so you’ll be able to hold a larger rock that way, maybe a few dozen tons. But try it with too big a rock, and eventually, that’ll fail, too: It’ll get too heavy for the forces holding it together.
If you’re trying to hold it against merely the Earth’s centrifugal force, then it gets much easier. The Earth’s centrifugal force is only about 0.3% as strong as its gravity, so you can hold a rock a few hundred times larger against the centripetal force, so maybe perhaps a thousand tons.
But we’re not trying to hold a few thousand tons. We’re trying to hold the entire planet. No material conceivable is strong enough to do that.
Interesting, submarines are built to endure pressure - not lack there of. If earth gravity shut off suddenly, the pressure under water would cease as well causing the subs to blow up like a balloon, yes?
ETA: Rethinking - probably not.
As I said upthread in response to @k9bfriender’ idea about subs, yes, as gravity suddenly shut off, the water pressure pushing inwards on the hull would also shut off.
But the resulting low pressure situation is the same as what the upper part of the hull experiences while the boat is on the surface. The pressure ~40 feet down at the bottom of the hull is more, but not vastly more. The sub survives that just fine. Likewise sitting in drydock surrounded by air. No bursting.
But you do make the completely valid point that the change would be sudden. IANA expert, but supposedly subs are compressed at least some by the water pressure at depth. The hull is squeezed and therefore shrinks, but not catastrophically so; metal is flexible up to a point.
In normal diving & surfacing, and even in emergency high-speed surfacing, that pressure is relieved more or less gradually over a span of minutes as the sub changes depth. If gravity disappeared instantly, so would the pressure disappear instantly. The sub would spring back to its surface size and shape almost instantly too. What breaks then? I sure don’t know but I wouldn’t be surprised to find something did.
The hull would still have to overcome the inertia of all the water around it. So it’s not going to instantly spring outward. Of course, the OP doesn’t say anything about what happens to inertia in this gravitation-free environment. I guess we have to assume it’s still there.
I said upthread that the Earth is going to blow (disintegrate) with no gravity and thought it’d be in a matter of minutes. After thinking about it, it’ll take hours, maybe days. The Earth will immediately start shedding air, water, and surface dirt and rocks. And keep doing so until it gets to some depth where the rocks are compressed by the overlying rocks, at which point the disintegration will accelerate.
Would it, though? At the surface, perhaps, but for a compressed unit of water at the bottom to expand from a compressed state (even for the tiny bit of compression that water is subject to) wouldn’t all the water ‘around it’ have to decompress too? At the speed of sound, presumably?
I.e. just before they fly off into space, the oceans have to spring back into their uncompressed volume ( maybe a couple inches higher over the deepest parts?) which will take time. It would certainly take a few minutes for the air to all blow away into space.
Thinking about this a little more, if gravity disappeared would the atmosphere not be violently and immediately sucked (blown?) into space? The difference between atmospheric pressure, which is dependent on gravity, and the vacuum of space is huge. That, along with the gasses in the ground trying to escape, and the sudden boiling of liquids, would seem to do more damage than inertia and any other forces. Would we even know what hit us, let alone have time to float to the ceiling, which was probably ripped away by the sudden explosion of the atmosphere anyway?
Again considering only centripetal force, the oceans won’t “fly” off into space as in “flung violently outwards”; instead they’ll drift inexorably off into space. Although I may have misunderstood which of the multiple meanings of “fly” you meant. They’ll certainly depart in an upward direction over time.
Good point about the time of water decompression. It won’t be zero for the reasons you say. Then again, Google tells me the speed of sound in sea water is on the order of 1500 meters per second. Good bet there are no submarines operating below 1500 meters = 4500 feet depth. So however deep the sub is, the time for the decompression of the ocean upwards is probably less than 1 second. Heck we can be generous and make it two seconds to allow for inertial effects in the water. Still quick, but not instant.
That’s a darn good point I think most of us have missed. I certainly missed it.
The atmospheric pressure and hence density gets real close to zero at about 100K feet. Down on the ground it’s about 15 psi and about 0.1 pound/cubic foot. All that air is going to be going straight up/out at the speed of sound. Which itself will diminish as the atmosphere vents to the vacuum above.
In military munitions design, an overpressure of just a few PSI is plenty to trash nearly any man-made structure except a bunker. The rather sudden application of ~15 psi to everything everywhere as the atmosphere departs will carry all the wreckage of what was civilization with it almost immediately.
I now say this is how the experiment ends. The atmosphere, and all the entrained gasses in the upper layers of the ocean and the land will blast outwards very quickly, as in a few seconds tops. The rest of the oceans & the rocky parts of the planet will take a lot longer by comparison. But also gain speed as the destruction drives deeper into the Earth’s interior. As @dtilque said just above.
Truly amazing volcanic eruptions happen when a heavy cap of rock fails, releasing the gas pressure in the magma below. It’s Mentos & Pepsi on a gigantic scale. Mt. St. Helens was one such event.
I’d bet we’d also get some really amazing volcanic eruptions occurring almost immediately; only the inertia of the rock caps would slow the gassy magma below. Vesuvius? Yellowstone Caldera supervolcano?
Think of a circle, you are standing on point A. As the earth rotates, let’s pick point B an hour later, 15° further on. But you without gravity continue straight along a tangent, the same distance as the arc to B but at point C.
ABC form a triangle, which we can approximate with a right-angle triangle. Approximate the arc AB with a straight line AB. The earth is 8,000 miles diameter, so 4,000 radius, roughly 24,000 miles circumference. In one hour, AB is about 1,000 miles.
By equal triangles rule (if I still remember my high school geometry) ABC is also 15° at the angle A. After an hour, you would have separated from earth by 1000(sin15) miles, or about 259 miles up in the … assuming it’s still there… air.
This approximation is probably close enough for anything under 15°.
This is an acceleration thing, so you don’t immediately launch at 259 mph. If t is in seconds, for each t=1 you can calculate the earth rotates 1/240 of a degree, or 1467 feet per second roughly (15 degrees into 1000 miles per hour, converted to feet and seconds).
h=dsin(t/240) where d=t1467
First second - h = (1467)sin(1/240) = 0.1 feet upward
30 seconds - h = (146730)sin(30/240) = 96 feet
60 seconds - h= 384 feet high.
That’s about 0.21 ft/sec^2 or about 0.007g (so in the ballpark of previous answers)
But, apparent acceleration upward due to the tangent path is cumulative, so you do “pick up speed” for while compared to the ground.
Of course, if the ground comes with you, all bets are off. So our speculation goes on the premise that the earth stays intact by the same magical means that gravity switched off. (In the movie Real Genius, one character says “would you be ready if gravity reversed itself?” which was also something I wondered about as a child…)
I do wonder - one of the lessons of Hurricane Andrew was to nail the roof rafters down with anchors, not just toe-nailed 2x4’s. (Plus, don’t skimp on the roofing nails). I wonder if that is sufficient to hold the roof on with that mild upward pull? I also assume that is code anywhere where high winds would be an issue. The wood frame of the house would stay intact due to the sheeting being nailed sideways into the frame. Generally floor joists are toe-nailed into place. Not sure if there is any positive connection between the base and the foundation, but I’m assuming building codes are a bit more strict than just “place it there”. Possibly the lack of gravity and steady upward pull would eventually loosen the soil and the buildings would start flying away one by one depending on the depth, cohesion, and dampness of the soil they are embedded in - slab houses and trailer parks go first? Concrete basements produce a suction effect and take longer…
Thanks for answering my questions, SD!
A related but more somber point -
The death toll in last week’s Turkish-Syrian earthquake is much higher because it happened in the middle of the night while a lot of people were at home asleep in those high-rise buildings. The toll might have been less during the daytime. Timing always matters.