A Mighty Woosh
If Earth suddenly stopped spinning, mayhem would ensue.
What would happen to the objects on the surface?
For simplicity , assume that the objects start near the equator.
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22 solutions
The atmosphere would still be moving at around 1000mph so pretty much everything would be caught up in a mega hurricane. It would be like being shot out of gun, so you'd have something of a ballistic trajectory.
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The mega hurricane, because it has friction, would actually slow objects down. If the objects did not have the required velocity to leave the Earth's surface before the stop in rotation, they certainly wouldn't after being slowed down, with the obvious exception of air resistance and lift which are not included in the question. Note that the range and speed of a bullet is fairly negligible compared to the size of the Earth.
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Yes, it is negligible in terms of the size of the earth. Whether it affects the answer depends on what is meant by "skid across the Earth's surface."
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@David Stewart – Skidding across the Earth's surface definitely should include - some objects being bounced around, - big objects collapsing, and - some stuff being launched temporarily, because of the potential energy of the things collapsing.
So I would say it would definitely be a rather wide interpretation of skidding across the surface. Still, it is the only option that makes sense out of those given. For individual objects C, or less likely B, or even less likely A, might apply, but for the wide majority D will definitely be the case.
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@Roland van Vliembergen – Of the options presented D is clearly the best, but it really only deals with the question of momentum and the effect of gravity. There are lots of other forces that would be at play.
I think the easiest way to think of the problem is to make yourself the frame of reference and imagine the earth suddenly moving at 1000 mph beneath you. You’d certainly skid some distance but you’d pretty quickly be engulfed in a very hot torrent as the atmosphere heats up and starts filling with debris. Then a local hill is likely to run into you at super sonic speed.
This is the crux of the problem, It is an impossible solution. The atmosphere is a part of the rotating earth. If improbably and contrary to the laws of physics the earth just stopped rotating without slowdown, nothing would happen because the same improbable forces that are at work on the earth would be at work on everything on the earth.
What about gravity? Does that come into play at all?
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Gravity is the reason objects stay on the surface. The method of this solution is that since the Earth has the same gravitational attraction regardless of how fast it is spinning (as the force of gravity is dependant on mass), gravity should work almost exactly the same before and after the halt in rotation. Thus we do not need any exact values; if objects had the momentum to counteract gravity after the halt in rotation they would have already flown off beforehand, which we know does not happen.
Were saying it just instantaneously stopped dead, not even a "foot off the accelerator and then slamming on the breaks" kinda thing? Cause if it just stopped like that, that's be one hell of a way to go. Ayah!
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Yea, wouldn't that tear the earth apart?
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Well, not the entire Earth. Maybe just the surface layer. The Earth is big enough for gravity to hold it all together in any circumstance. Actually, something suddenly stopping like this is physically impossible, but hey, it's all hypothetical.
https://image.gsfc.nasa.gov/poetry/ask/q1168.html
Doesn’t the effect (skid vs fly off a bit) depend upon the mass of the object?
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Gravitational acceleration is the same regardless of mass. If an object gets launched up, it would be because of running into something on the ground, or air resistance and lift. In either case, this path of motion is not tangent to the Earth's surface, and so the answer cannot be any of the other options.
Joan, I had this problem too, because I was trying to explain why answer "d" was correct. It seemed intuitive at first, but after, "because, drrr...gravity.", I was trying to explain this to friends and used an analogy of, "Say you're a passenger in a car and you happened to neglect to use your seatbelt. The driver unexpectedly crashes into an immovable (concrete) object. What happens to you?" To co-opt your phrase, they answered, I crash through the windscreen and then "fly off a bit" :) and then land and skid across the pavement (i.e. - they answered "C").
Maybe I used a bad analogy because it didn't take into consideration scale (wee humans vs. earth gravitational pull). Not so much mass as the ratio between mass vs. velocity?
Would someone please explain why "C" is not correct in layman's terms so I can share it with some of my friends? (non-sciency people). Thank you. :)
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When you are in the car, you are already moving relative to the ground, despite the fact that you are stationary relative to the car. This is the same for the Earth: if you are stationary relative to the ground, you are still rotating relative to the centre of the Earth, because the entire Earth is spinning.
In a car, your motion is in a straight line. As soon as you crash, you continue in a straight line, through the windscreen. Now, consider what happens when the Earth stops spinning: if you retain the same momentum, which you do, you should continue around the same path as before. As it happens, that path is following the Earth's curvature.
The point of my solution is that the rotation of the Earth has no effect on the gravitational force between you and the Earth, so if the Earth stopped spinning, and was completely smooth frictionless, nothing would change; objects on its surface would still continue in the same circular motion. Thus, if an object were able to "fly off a bit" after the Earth stopped spinning, it should have already "flown off a bit" before the Earth stopped spinning, which we know doesn't happen.
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@Joseph Newton – Thank you! It was the "stationary relative to..." part that I was having difficulty articulating.
things on the moon are stationary, are they not.
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Depends from which reference frame; they are obviously not stationary relative to the Earth. How does the moon come into this?
The moon does not turn on an axis.
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Yes it does. It takes 27.32 days. We see the same side of the moon because it's rotational period and orbit are the same.
consider any traveling vehicle of which you occupy, a train, a car, a boat. It stops and you go flying, into the windshield, into the water.
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That is because you retain the same velocity as before. You accelerate relative to the vehicle, but relative to the ground your motion stays the same. My solution is considering how objects move relative to the centre of the Earth, and the force of gravity is enough to keep objects from flying off into space regardless of whether the Earth is rotating under them or not.
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Sooooo, you contend that gravity hold something or some one to the ground as a condition of the earth spinning or is it the electromagnet field. The electrical charge you get when you grab hold of electricity. Then they turn it off and the electrical force is not there.
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@Frank Salinas – It is gravity. The electromagnetic field is negligible. The main point of my solution is that objects that could fly off into space without the Earth spinning should also be able to fly off into space with the Earth spinning, because whether the Earth is spinning or not should have no effect on gravity. Since objects don't fly away with the Earth spinning, we can conclude they don't fly away without the earth spinning.
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@Joseph Newton – I agree. What creates the gravity? Mass, energy, other?
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@Frank Salinas – Earth's gravity comes from all its mass. All its mass makes a combined gravitational pull on all the mass in your body. That's what gives you weight. And if you were on a planet with less mass than Earth, you would weigh less than you do here. Your premise of the earth stopping abruptly could not happen. If anything the earth would slowly decelerate. Like a train, a car, or a boat that ran out of gas.
And there was me looking up the rotational speed of the earth and the orbital speed on earth's surface…
Ah yes, that's obviously true. I knew the tangential velocity wasn't anywhere near escape velocity but I failed to apply that simple logic. Slightly embarrassed now.
I don't see this as a "Basic" question. I see it as "Intermediate."
Let's imagine we have a solid ball on a frictionless Earth's surface. The circumference of the Earth is (let's say) approximately 2 4 , 0 0 0 miles, which means the ball is moving at a maximum speed of about 1 , 0 0 0 miles per hour (only at the equator). The orbital speed around the Earth near the surface is approximately 1 8 , 0 0 0 miles per hour. This is the reason why the solid ball stays put. Let's suppose a day is not 2 4 hours, but only 3 4 hours. Then the ball will be moving at a maximum speed of about 1 8 , 0 0 0 miles per hour at the equator. What will happen is that the ball will become weightless but still stay where it is. If the Earth were to then stop moving, the ball will be in orbit around the Earth just above its surface.
In other words, even in the extreme case of a day only 3 4 hours long, the ball will appear to "skid across the Earth's surface, following its curvature". The same would be true for any day longer than 3 4 hours.
Objects at latitudes other than the equator will drift down towards lower latitudes, which can be easily visualized by holding a straight edge tangent to the circle of an object's latitude on the surface of the sphere. So, for example, objects near the North Pole will drift nearly southward. If the Earth's surface is frictionless, then everything will move endlessly in great circles.
If an object were to fly off the surface of the Earth if the Earth were to stop, that object would have to fly off the Earth now. Nothing is holding it but gravity, and in this far fetched scenario I am assuming gravity still works. If it doesn't, the problem should state so.
Also, while the graphic indicates the object is on the equator, the text does not. Some may think this may influence the solution.
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If gravity was shut off too, then everything will fly off in tangents into space. But with the gravity still on, everything will skid along the surface in some direction. Nothing would leave the ground.
I am not seeing your answer, because I don't see gravity still working, my understanding from geology and solar systems courses is that the magnetic field is created by the spinning of earth and the elements therein. Without the spin, as I understand it, we have no gravity. Tests that I have participated in seem to verify this.
Could you provide an explanation for how gravity continues when no energy is being applied that creates magnetism?
I am theorizing that that one answer may be that the magnetism of electrons to the nucleus of their own atoms would not have abated, and the pull, though lessened, would then still be considerable. We know that matter in space still has atomic structure in spite of the lack of a magnetic contribution from the spinning of the entire object.
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Gravity is a property of mass, not a property of magnetism. https://www.youtube.com/watch?v=Xc4xYacTu-E
We have a flat earther here lol
I have never really done any astronomy before in my life but I decided to give this problem a shot. I don't really get the reason why the objects will skid across the surface, what causes them to do that. I would rate this problem a 9 because I still don't really understand it. While solving this problem, I didn't really know what it meant and I didn't really get it.
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Let's say you're sitting in the back of a moving pickup truck. If the truck suddenly stops, you're going to skid forward. it's the same thing here. Right now the Earth is spinning, so that you are likely to be moving a few hundred miles per hour, even though it doens't feel like it. If the Earth were to suddenly stop spinning, you're going to lurch forward towards East a few hundred miles per hour. This problem is really about whether or not you'll also leave the ground. The answer is no, you need to be moving a lot faster in order to leave the ground, even if only temporarily.
Please don't use miles...
If the earth were to stop spinning in the next second, in order for us to orbit at the surface of the earth; the square of the velocity with which we move must be equal to g × radius of the earth.
I.e v^2 = gR
The surface of earth (near equator) moves with 463.17 mps approximately. gR near the equator is about 6.24 × 10^7
Putting the values in the equation we see that v^2 is in fact not equal to gR.
Now this means that the gravitational force we experience is more that that required for circular motion. So, if the earth suddenly stopped spinning. We sure would skid along the surface of earth but this not means we're orbiting the earth. Instead we would continue to some distance and eventually stop. However other effects would we more dangerous than this one like we won't have day cycles and temperature of one side will rise up enormously and stuff.
The dependence of a planet's acceleration due to gravity at a point on it's surface and angular velocity of the planet is given by
g(φ)=g-R(ω^2)•cos^2(φ), where "g(φ)" is the gravity at the latitude angle φ "ω" is the planet's uniform angular velocity about it's axis (NS); "R" is the radius of the plane(the planet is usually assumed to be a uniform sphere); "φ" is the latitude; "g" is the acceleration due to gravity at the poles(which is the maximum possible value of g(φ) ). Although there are some approximations in the formula, that doesn't matter(Note that this formula was taught to us in class XI and I'm still a student and therefore don't consider my words to be having a strong base). So, coming to the question, where the angular velocity of earth becomes zero, the second term in the formula becomes zero and thus acceleration due to gravity on every point of the earth's surface becomes same(at the equator, your weight slightly increases and....). So what I want to conclude is that option 'D' might also be considered as correct answer...
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I love this app! How did I not find it earlier?
@Sai Ram Charan Panguluri Your inference just means that when the earth has stopped rotating then the gravitational acceleration at the surface of earth is uniform everywhere and it has nothing to do with the motion of an object when the earth will stop spinning. For an object kept at the equator, v^2 = gR will always be the equation which will determine whether the object will orbit at the surface or not.
P.S If you want to figure out what happens to an object some where at the tropical line then we have the equation v^2 = gR + f(Φ) where f(Φ) is some function of angular position (latitude) and this function can be calculated easil but I'll give you a qualitative analysis ; when earth stops spinning, an object not at the equator will also move to some distance along the latitudnal line and will try to move to some distance towards the equator. I'll leave it to you to verify that.
The Earth stopping in any time less than billions of years would lead to level 10 earthquakes- solid rocks are not capable of relieving stresses.
We don’t have to think about day/night and temperature because we are all dead when this happens. Imagine we are in a car of speed 1000 miles/hour and it crash. We would have no chance of survival.
All of these other explanations seem way overthought. I got the right answer simply by remembering that Earth's gravity is not caused by the centrifugal force of Earth's rotation but instead, the curvature of spacetime. Or to put it in layman's terms, if Earth stoped rotating, it would still have gravity, so all of the answers where things fly off were eliminated because with gravity intact, the only option is that objects would skid on the surface because they would still be in motion and gravity would keep them on the surface.
Could you explain a bit concerning the curvature of space time. I am assuming (very dangerous, I know) that this is a reference to quantum physics.
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Simply put, gravity still applies even the Earth stops spinning. There's no reason why any objects would start flying off, there is always a force pushing them down on the surface.
Not quantum physics so much, but same era: the Einsteinian view of how the Whole Thing is.
Yup. I was surprised to see such technical explainations.
Let's say you were spinning around while holding a string with a ball tied to the end. By spinning around while constantly facing the ball and keeping string straight, this can model the objects on Earth's surface while it rotates. If you were to suddenly stop spinning, the string would wrap around you, and the ball would eventually hit you. Now imagine that the ball was on Earth's surface. The ball would've skidded along the surface, but the ball isn't on a surface so it came crashing into you.
Sorry but in my opinion this is another poor question. If the planet suddenly stopped spinning objects would skid across the surface mostly at the equator. The oceans wold wipe out everything on land with diminishing affect to zero at the poles.
Hey John, nobody asked what would happen to the ocean or land mass. Just an object. Don’t overthink a question meant to be taken lightly, then blame it on the person who wrote the question. Especially when they are just trying to spark some thought from young minds. And yes I’m glad you realize it’s just your opinion. So maybe it’s best to keep it to yourself.
Hi, in my opinion, it not fair to think about the floods taking over everything because clearly intentions of the problem is to ask how would an object move over land if the Earth stopped spinning suddenly.
We need to consider two forces here to analyse this problem
- Force of gravity
Gravity is the force pulls the body down on earth. There is no change in gravitational force whether earth rotates or not.
- Inertia force
Experienced by the body moving(rotating) along with the earth. Like we sitting/standing in a moving bus.
When earth stops rotating, there is no change is force of gravity, thus we remain on the surface but the inertia force moves us along the earth surface. (Like when bus stops, passengers doesn't get airborne. They just swing forward)
Only when radius of Earth bigger than semi major axis of GEO, object on Earth would fly around Earth in space. Because gravity is still, so A is wrong: it just enabeld when we remove gravity. And also B and C is wrong because object hasn't enouge velocity to leave surface. First cosmic velocity V 1 = 7 . 9 k m / s , and rotation speed of Earth at the equator V r = 8 6 1 6 4 s 2 × 3 . 1 4 × 6 3 7 1 k m = 0 . 4 6 4 5 k m / s . Because V 1 > V r , so it can't fly out of surface. So true answer is D.
Because the Earth suddenly stopping its spin wouldn't change Gravity, we can rule out A—they wouldn't fly off the earth in a straight line.
The Earth's spin at the equator (the fastest) is ~1000 mph (or ~447m/s). Geosynchronous orbit (where an object orbits at the same rate the earth rotates) is ~6710mph or ~3000m/s at 35,786km/22,236 miles altitude. The International Space Station is in Low Earth Orbit (approximately 408km; LEO is 160km to 2000km) and has an orbital velocity of 17,150mph or ~7666m/s. The closer you are, the faster you have to go. Even ignoring air resistance, 1000mph just isn't fast enough to enter orbit. So B is not right.
Let's check C. Much for the same reason as B, we just don't spin fast enough to have any real arc. The Earth's curvature is 'about 8 inches per mile'. Basic trig gives us about 0.008 degrees—you'll leave the ground for a fleeting moment, or perhaps more accurately, you'll be thrown the tiniest bit further before you fell over and started skidding along the ground.
Through process of elimination, the answer is D.
Yeah, I don't buy the elimination of C. A ballistic arc is a ballistic arc, even if it's very small. If you and everything around you were suddenly shot out of a canon horizontally at ~1000mph, "skid" is not the first or best word to describe what happens.
If you shout out a cannon ball perfectly horizontal at "only" 1000 mph, then the starting height is the maximum height it will get. To really gain height you need a speed high enough so all the gravity force the earth is making to the object is "used" to maintain the circular motion, so that object would be "weightless". In this limit the objects could take a trajectory like C. This is, a speed equal to \sqrt{g*R} ~ 17700 mph. So C is eliminated.
The question was about the (spinning), the earth has many movements, around itself, around the sun, with the sun around the galaxy and with the galaxy where the galaxy itself is moving. The objects on earth my fly if the earth stops both of the spinnings around itself and around the sun. This would have a greater impact than just stop spinning.
Can the reason for the answer also be Inertia (Newton's First Law)?
I just assumed the earth was a bucket and the object was water if i'm rotating the bucket the water would still stay in but if i let go the water (object) would still be inside, of course that's my way of seeing the proplem. Hope you liked it. Also because of this explanation i got the question correct
As many have already stated, objects in the surface do not already have the energy required to become airborne. Another fact is that the perceived effect of gravity would increase slightly due to the lack of centripetal force of the rotation of the Earth. That's even more reason to believe that nothing would escape Earth's gravity.
Even if Earth stopped spinning, there is still gravity, which is pushing you down, therefore you will not fly off.
It's D because earth stopped, but gravity still exists.
D is what is already happening to us. Earth suddenly stopping won't change gravity!
I misinterpreted the way the answers were phrased. I thought the correct answer was that the objects would movie straight on a relatively infinitesimally small tangent to the surface and arc immediately downward, which in effect looks the same as skidding on the surface. I guess I should have taken the image they provided more literally before answering C.
I did a science project on this in 4th grade; it is D because the objects would keep moving along Earth’s surface at its speed, since we are not glued to the ground. Only the earth stops, and the objects stop when they hit some sort of force (for example a wall). Hope this helped^_^
The objects on earth would not move faster than they already are if the earth stopped suddenly, they would just keep going at the same speed, because they currently do not fly away from earth I would assume that the same would apply if the earth was not spinning.
It depends on how fast is the rotation. In ordinary speed of the earth is of 1 thousand miles/hr will only skid us in a due to gravity. Friction is also one of the factors if you will skid in a smooth surface, but still you if your distance in only as far as Italy to Iceland the surface is nearly flat on earth's surface.
If earth stops spinning, it would not have any fundamental affect on the gravity using which earth pulls on stuff. So the question of flying off is out of question. Secondly, the impact would be similar to the force which act on our bodies when a fast moving bus suddenly comes to a halt. We may skid along the surface but in the end once the initial impact is over the body would come to rest.
Any trajectory where the object would left the ground, would happen with or without stopping earth normal rotation.
It is assumed that whatever stops Earth rotation doesn't stop the object's velocity, and this is imparted to the objects by the rotation... meaning the initial velocity that configures their trajectory is the same with the rotation or not. Since surface objects don't take-off by themselves by definition, it is safe to exclude any trajectory proposed where that happens.
What if the earth spun twice as fast as it does now (12 hour days instead of 24) and then stopped.....would that make a difference in the answer? If it does, then is it just coincidental that the earth's current rotational speed makes objects slide along the surface, and that objects would get launched along a parabolic path until it landed back on earth's surface at greater rotational speeds?
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Actually no, that wouldn't change my answer. The operational word is "surface" (objects).
Surface objects are, I assumed this definition, objects that's stay fixed to earth surface. That happens through two pathways: either they are disconnected from the surface but stay quiet because their natural movement is blocked by surface contact forces, or, they are chemically connected to surface Earth and in that case, we'll exclude them because that made them part of the surface, which must also be stopped. In the present moment, fixed objects of the first kind have a "naturally" trajectory due to gravity forces which is an ellipse... where they are in the most distant position from the center of the ellipse. They "want" to "dive" below surface but they can't. Had Earth rotation more speed imparting to the object, and the ellipse would have be more open but still, diving into Earth, unless... if Earth is rotating a little more than 16 times faster and your object is in the equator, the centripetal force might correspond to the gravity one, and the natural trajectory will be a circle coinciding with the Earth surface. Stop Earth and the object will continue its circular movement. Or, the rotation is faster, and the centrifugal force will exceed the gravity... but in that case, we cannot call the object a surface one because he will not stay on it, stopped Earth or not.
If objects on the Earth's surface travelled at a rotational speed such that they could become airborne, then the Earth wouldn't need to stop rotating; objects would already be flung off due to their momentum. However, we know from experimental evidence that objects on the Earth's surface do not have the velocity to fly away of their own accord, so if the Earth stopped rotating the objects would just skid along the Earth's surface.