1. Aug 11, 2011

nami habib

if a tunnel is bored through the centre of the earth and a pebble is dropped into it then the pebble will do what ?....A)stop at centre...b)perform s.h.m.

2. Aug 11, 2011

SHM for a considerable period of time, given that it would have gained enough momentum to defy gravity and travel to the other end of the hole by the time it reaches the centre. And then gravity pulls it right back.

[EDIT: And that's if the hole is drilled from pole to pole.]

3. Aug 12, 2011

torquil

But you are neglecting the considerable air resistance. So it will not be close to SHM in the beginning.

I'm of course assuming that molten rock/metal will not refill the hole when the drill is removed...

4. Aug 12, 2011

Ryan_m_b

Staff Emeritus
Assuming the tunnel was bored through a perfectly spherical Earth and was in a vacuum then it would SHM for quite a while if not indefinitely.

5. Aug 12, 2011

HallsofIvy

IF you are ignoring air resistance then you will have harmonic motion- just as vhbelvadi says. Energy will be conserved so the pebble will accelerate until it reaches the center of the earth, decelerate so that it stops just as it reaches the surface at the other end of the tunnel, then repeat its motion.

IF you are not ignoring air resistance, then Energy is not conserved. Depending upon just how much energy is lost to friction, the pebble may perform "damped" harmonic motion for several repetitions, eventually stopping at the center of the earth, as torquil says.

6. Aug 12, 2011

nami habib

thnx guys

7. Aug 12, 2011