o In general , F1 + F2 + F3 + ------ + Fn = 0
Friction o Friction is a contact force that opposes relative motion . o No friction exists till an external force is applied . There are 3 types of Friction : o
Static friction o
o
Force that resists initiation of motion of one body over another with which it is in contact
Opposes Impending motion o
Denoted by fs Let the ball be at rest initially Applied force , Fa = 0 ; Static friction , fs = 0