# Toronto Math Forum

## APM346-2015S => APM346--Home Assignments => HA8 => Topic started by: Chaojie Li on March 19, 2015, 09:13:07 PM

Title: Solution of Question 4
Post by: Chaojie Li on March 19, 2015, 09:13:07 PM
Using Newton shell theorem (see [Section 6 of Lecture 25]) prove that if Earth was a homogeneous solid ball then the gravity pull inside of it would be proportional to the distance to the center.
Title: Re: Solution of Question 4
Post by: Chaojie Li on March 19, 2015, 09:14:32 PM
Yes exactly: if you drill a tunnel and drop a ball it will be a harmonic oscillations $r'' = - kr$ with $k= g/R$.