W01M04 Vibrations of SDOF Systems 

excellent lecture sir... finally found a good teacher of this subject

For inelastic systems the stiffness force should be K(u).u as u have explained it in one of your earlier videos?

periodic motion and oscillatory motion are different. a periodic motion has a time interval after which it repeats. oscillatory motion is also periodic motion but there is an extra condition that an oscillatory motion has a mean position about which it goes to and fro

make a detailed video of these lectures

not understood properly