Question
A particle is vibrating in a straight line with amplitude A. What is the total distance travelled and displacement of particle in one complete oscillation?
Solution
Let the particle be vibrating between points L and M.
In one complete vibration the particle moves from O to L, then from L to O and then from O to M and finally from M to O as shown in figure. 
Therefore the total distance travelled by particle in one complete oscillation is,
S = SOL + SLO + SOM + SMO
= A + A + A + A = 4A
As the particle comes back to same position after one complete oscillation, therefore the net displacement of particle is zero.
