Bottomless pit
Discussion
Question in today's Times debate section:
If it were possible to dig a bottomless pit, right through the core of the earth and coming out the other side (notwithstanding temperature etc) then, if you dropped a stone down the hole would it decelerate and hang in suspended state at the equivalent of the Earth's centre?
If it were possible to dig a bottomless pit, right through the core of the earth and coming out the other side (notwithstanding temperature etc) then, if you dropped a stone down the hole would it decelerate and hang in suspended state at the equivalent of the Earth's centre?
Question in today's Times debate section:
If it were possible to dig a bottomless pit, right through the core of the earth and coming out the other side (notwithstanding temperature etc) then, if you dropped a stone down the hole would it decelerate and hang in suspended state at the equivalent of the Earth's centre?
The terminal velocity will vary from stone but it wont be enought to achieve escape velocity (assuming consistent atmospheric density).
As a result the stone would "yo-yo" up and down and eventually come to a rest dead centre of the hole.
Think of it as rolling a ball into a bowl. It will never quite reach the other side and will eventually come to a halt in the middle.
What would attract the stone "down" the hole? If the hole goes all the way through the centre of the earth there is no mass to attract the stone. I believe it would come down to the atmospheric pressure differences at each end which would create a "wind" through the hole, which would force an object one way or the other.
Jinx said: What would attract the stone "down" the hole? If the hole goes all the way through the centre of the earth there is no mass to attract the stone. I believe it would come down to the atmospheric pressure differences at each end which would create a "wind" through the hole, which would force an object one way or the other.
Even if there is a hole in the middle, then the pull will still be towards the centre of mass, which in this case would be a hollow space.
P*Ting said: Gravity doesn't work in straight lines. Think of it is analagous (sp?) to magnetism.
If you have something metal and an earth shaped magnet the metal something will be pulled towards the centre of the magnet, the fact there's a dirty great hole in it just reduces the force a bit.
I thought gravity DID work in straight lines, they are only viewed as curved as a way of visualising space-time distortion...
Correct me here if im wrong though, please.
Yep, gravity distorts time (Einstein) so this is just a question of dynamics. I think it would fall towards the centre and then oscillate until it came to a dead stop in the centre. It would stop in the centre because assuming that the earth is a perfect sphere the mass of the earth would be pulling equally from all directions on the stone... so eventually it would stop... yeah, I think I've convinced myself now
What a weird question to ask ...lol.
I reckon itd fall into the hole, go flyin almost say a third of the way past the middle , then eventually stop dead centre, cos all the forces acting on it would be cancelled out....ahem...
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But thats just given me a weirder thought: What would happen if you attached a torch to the front of a missile and fired it at the speed of light....would the light still come out? Would the light be travelling faster than the speed of light?....My head hurts..
I reckon itd fall into the hole, go flyin almost say a third of the way past the middle , then eventually stop dead centre, cos all the forces acting on it would be cancelled out....ahem...
. But thats just given me a weirder thought: What would happen if you attached a torch to the front of a missile and fired it at the speed of light....would the light still come out? Would the light be travelling faster than the speed of light?....My head hurts..
Jinx said: What would attract the stone "down" the hole? If the hole goes all the way through the centre of the earth there is no mass to attract the stone. I believe it would come down to the atmospheric pressure differences at each end which would create a "wind" through the hole, which would force an object one way or the other.
Nerdy boy says that if we think of the earth in this problem as two hemispheres then if we are droping the stone from north to south initially most of the 'pull' would come from the southern hemisphere. The amount of 'pull' from the south would decrease as the stone falls but this would be equalled by an equal amount of 'pull' from the northern hemisphere. When the stone is in the centre of the earth both northern and southern hemispheres are exerting an equal force on the stone, so there is no net force in any direction and (according to Newton) no acceleration.
This makes me revise my earlier theory about the stone oscillating around the centre. I think the stone would fall, eventually reaching a terminal velocity. It would then experience a 'braking' force from the hemisphere it had fallen through which would slow the stone until its velocity was reduced to zero at the dead centre of the earth... Thank you and goodnight!!
??This is not a subject for debate as such, since the answer is pretty easy, and anyone with a good understanding of Newton's Laws ought to be able to answer it. Assuming : holes were dug N and S pole, earth is homogeneous, stationary air in hole, perfectly spherical stone: the stone will accelerate until it has reached the centre, then start to decelerate, until it eventually starts to fall back toward the centre. Repeat until stone is stationary due to frictional losses with air.
Question in today's Times debate section:
If it were possible to dig a bottomless pit, right through the core of the earth and coming out the other side (notwithstanding temperature etc) then, if you dropped a stone down the hole would it decelerate and hang in suspended state at the equivalent of the Earth's centre?
If the holes are not at the poles, then the coriolis effect will lead to the stone experiencing an apparent force (due to the rotation of the earth) orthogonal to its velocity, which would mean it would repeatedly hit the side of the hole. Otherwise as above.
Incidentally, gravitational forces anywhere inside an homgeneous hollow sphere sum to zero. Basic 'A' level phsyics.
>> Edited by MEMSDesign on Thursday 6th February 13:52
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