Question

why is a oscillatory motion always periodic but a periodic motion may not be oscillatory ?​

Answer 1

Oscillatory motion means to and fro motion or back and forth motion. For example motion of a pendulum etc.

Periodic motion is the motion that repeats itself after a fixed interval of time.

Now oscillatory motions always repeat after certain interval of time, thus they are periodic but all periodic motion are not oscillatory. Like motion of planets around sun is periodic as because it repeats itself after sometime but cannot be said to perform to and fro motion so they are not oscillatory motion.

Answer 2

Oscillatory motion is the motion in which a body goes to and forth like in a swing or pendulum. A body in periodic motion repeats its path at certain interval of time. For example, a body in circular motion with constant speed.

One can say that all oscillatory motion are periodic but all periodic motion are not oscillatory.

Hope it is clear to you!!

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