Hole straight through the Earth?

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Discussion Overview

The discussion revolves around the hypothetical scenario of dropping an object through a hole that passes straight through the center of the Earth. Participants explore the motion of the object, considering factors such as oscillation, energy conservation, and the effects of Earth's rotation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that the object will oscillate back and forth due to kinetic energy, similar to a pendulum, assuming no air resistance.
  • Others argue that the object will pass through the center, slow down, and eventually stop before emerging on the other side, influenced by factors like air resistance and Earth's shape.
  • A participant mentions that the force on the object as it falls is a linear relationship, suggesting simple harmonic motion if air resistance is neglected.
  • One participant introduces the consideration of Earth's rotation, noting that the object would collide with the wall of the tunnel due to the Earth's movement during its descent.
  • Another participant acknowledges the thought experiment nature of the discussion while highlighting the implications of Earth's rotation.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the motion of the object, particularly concerning the effects of air resistance and Earth's rotation. The discussion remains unresolved with no consensus on the final outcome.

Contextual Notes

Key assumptions include the neglect of air resistance, the perfect spherical shape of the Earth, and homogeneous mass distribution, all of which are challenged by participants as unrealistic.

Holocene
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If a hole is somehow made to pass straight through the center of the Earth, and out on the opposite side, what would happen to an object dropped down the hole from one side?

Would it stop and "hover" at the center? Or would it fall straight through to the other side, and than fall back again and again?
 
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It will oscillate back and forward because there is a kinetic energy involved.
 
The action is similar to a pendulum. It will slow down only through friction (air resistance).
 
Oscillate back and forth through the center of the earth.
What will happen is when it will reach the center, it will possesses enough kinetic energy and will pass through the center.
Then it will slow down, building Potential Energy and will stop after emerging at the other side.
Then it will fall again, and the cycle will continue...

Important assumptions made are.
1)There is no air resistance.
2)Earth is a perfect sphere.
3)Mass is distributed homogeneously throughout the earth.

All are actually false and the first two will start affecting the motion and will start opposing its motion, so that, each time it stops before emerging out the other surface and will start slowing down.
This dampening will continue and after a huge amount of time, it will virtually stop at the center of the earth.
 
If you work out the force on the dropped object as a function of its distance from the center of the earth, you will find that it is a linear relationship (i.e., F = k * x), so it would be simple harmonic motion (this is, of course, neglecting air resistance).
 
It will hit the Eastern wall of the hole.
 
Granted this is a thought experiment, but Lurch mentions a wrinkle that I'm surprised no one else has: the Earth rotates. In the ~90 minute passage of the dropped object, the Earth will have rotated 22.5 degrees. The object will collide with the wall of the tunnel.

You'd have to do this experiment along the polar axis.
 
lurch mentioned a good point...
 

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