Something has been bugging me a bit as of late.
Imagine a hole being drilled down through the center of the earth and actually reaching the surface on the other side. A tube is then inserted into the hole and pushed all the way through. (Like a drinking straw piercing an orange.)
What happens when an object is dropped into one end of the tube?
My guess is that the object would travel past the center of the earth and then gravity would again pull it back toward the center point, which it would again pass but to a lesser degree. Eventually the object's position would be "stabilized" at the center of the sphere, perpetually floating in place. :cool2
Any other ideas?
lw
interesting question.
gravity would keep it close to the earth's surface - would centrifugul force allow it to satellite around the earth?
Interesting take, sistah-j.
However, in my reality, the object would be working with gravity until it passed the center of the earth and then it would be straining against gravity as it made its way toward the surface.
My guess on the centrifugal force issue would be that it would take an initial muzzle velocity greater than just gravity to allow the object to actually reach the surface on the other side of the earth and maybe launch into orbit.
THanks for playing along, sistah. :smoke2:
lw
falling down, down, down, but the earth is spinning. how long a trip is it from side to side?
i think we'd have to build a model and replicate some galactical forces in order to observe.
obviously, my mind is somewhere between the hole in the orange and Star Trek blasts through the cosmos.
The poor object is without any additional force except those acting upon its own weight from without.
And, worse, it's warm in the earth's core. Wouldn't the thing simply burn up before it got a chance to traverse mid-point?
Or is the tube protected from those x-treme temperatures?
OK... Let's protect the tube from the heat.
However, the object is only falling down until it reaches the center of the earth. Then it is falling up. :e_surprised:
lw
the earth spins round once every 24 hrs.
How long a trip is it from surface to mid-point?
would not the object be also falling sideways. ( as you projected, falling up looms into the equation, or not?)
What is gravity within the earth's surface? what is down?
i need to see this, my mind isn't able to construct the physical reality. There has to be a physicist who can talk me through this.
Where are the physicists among us? This question is fascinating, lw.
Quote from: "judih"Where are the physicists among us? This question is fascinating, lw.
Yah, I've got a degree in Physics, but I'm a little rusty on the ordinary differential equations needed to give a good answer -- university was a long time ago.
Approaching it as a physicist, you have to adopt a simplified model. Ignoring the rotation of the earth and air resistance for the nonce, the object will fall to the center, start moving back up, slowing down until it reaches the antipodes, at which point it begins "falling down" again. This will repeat forever. (As good physicists, we'll assume a spherical earth, because the equations come out more elegantly that way.)
If we account for air resistance on each segment of the journey will will move less far, eventually becoming stationary, "floating" at the center of the earth.
If you want to account for the rotation of the earth you should probably speak with someone who's knowledge is a little more fresh -- unless you do it at the poles, in which case you can ignore the rotation. If you want to accurately account for the sordid details of air resistance you should probably talk to one of those engineering types (yuck!).
...oh, and I think you'll want to assume that the earth has uniform density. My intuition tells me that if you do that the downward force becomes a simple function of distance from the center of the earth, making the ODE's simple. But to justify that intuition... like I said, University was a long time ago....
Thanks, amom.
But now please explain to me the science behind the idea of an object "floating" without visible means of support. Does this mean gravity can be a physical place or just stronger in this particular physical space? :beek:
lw
Each little bit of the earth -- every molecule, if you will -- pulls on the object with a gravitational force. But because you're at the center of the earth (again, it is best to assume uniform density and sphericity) the symmetry of the situation exactly balances. For every little bit at one distance and in one direction there is another little bit at the same distance and in an opposite direction, canceling each other out. The net force is zero, and as F=ma (force = mass * acceleration, Newton's law) a zero force means a zero acceleration.
I saw a cool animated demonstration of this on PBS about a year ago. Dr. Nye the Science Guy, or something like that.
The object takes on enormous speed the farther it drops, and begins decreasing as it arrives at the opposite side. There is math behind this, for those who know the formula; and unless stopped, it will fall again and repeat the cycel. In reality, nothing we have now would prevent the falling object from heat perhaps more than the surface of the sun.
Thanks amon,
I thought of doing this at the poles, but seeing lw didn't start the question at that location, i left it aside. It absolutely makes it simpler, and I like your inclusion of Einstein's equation: a simple, recognizable equation makes life so much 'neater'.
Kosmo, your observation seems reasonable and should be addressed before the actual attempt.
lw - thanks for the thoughts, so far.