Which feels a greater pull due to the earths gravity: a 10-kg stone or a 20-kg stone? If you drop the two stones, why doesnt the 20-kg stone fall with twice the acceleration of the 10-kg stone? Explain.

● All particles attract each other through gravity ● Force on x by y = force on y by x ● Inverse square law: double the distance, force/4 ● Fg = G*M*m/r^2 ● Don’t forget though that f=ma , so small things fall towards the earth quickly, while the earth doesn’t move ● Cavendish used a torsion balance to determine G ○ Gravity produced torque on the bar - used that to solve for G ● Grav potential energy: ○ W = Force dot distance ■ Force is attractive (gets a -) ○ GMm/r1 - GMm/r2 = W ● To determine escape velocity: set ½ mv^2 = GMm/r(earth) ○ Simplifies to v = sqrt (2GM/r(earth)) Chapter 21: Electrostatics ● Electrostatics deals with the charges, fields and forces on and around unmoving charged particles. ● Force between two