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Oscillatory motion is the type of motion where object moves to and fro about a mean position.
Periodic motion is the type of motion where object repeats its motion after a fixed interval of time (or its integer multiples). The smallest such interval is called time period.
For a sound wave, loudness increases with amplitude of the wave.
Pendulum works on the principle of gravity. When displaced from its mean position, it is gravity that pulls the bob to its mean position.