An interesting thought experiment about oscillation is the hypothetical motion of an object dropped down a hole that extends from one side of the earth, through its center, to the other side of the earth.
With the (admittedly unrealistic) assumption that the earth is a sphere of uniform density, a) prove that the motion is simple harmonic, and
b) calculate the period T of the objects oscillatory motion.
Hints:
a) Take note of the formula on Slide 2 of lecture note file Lec 28 which gives the
functional dependence of the gravitational restoring force F pulling the object
toward the center of the earth in terms of the objectās radial distance r from the
center of the earth, when r ? RE .
Then, use Newtonās Second Law with this formula to derive how the objectās acceleration a and its displacement r from equilibrium are related in the
SHM manner shown in the third equation up from the bottom of Slide 4
of lecture note file Lec 29.
b) The proportionality constant for how a depends on r is just the square of the
angular frequency ? of the oscillation.
From ?, you can then calculate T = 2 ? / ? .