Periodic and non-periodic change
Depending on whether or not a change repeats itself after a definite period of time, it can be classified as periodic change or a non-periodic change.
Changes that repeat themselves after a definite interval of time are called periodic changes.
Rotation and Revolution of earth, beating of the heart, clock striking every hour, motion of the seconds-hand / minute-hand / hour-hand of a clock are some examples of periodic changes.
Every year we observe that seasons changes. We go from rains to winter and winter to summer and so on.
* What types of clothes are worn in winter? Beanie, Sweater, Gloves, Fleece jacket, Jeans, Mittens, Scarf, Socks
* What are the clothes that we wear in summer? Cotton dress
If the winter season changes into summer, we observe change in the texture type of clothes we wear. We wear woolen clothes in winter and cotton clothes in summer. Similarly, we observe that the winter season is cool and summer season is hot. In winter, duration of night is longer than in summer. We take cold drinks in summer but prefer hot tea, coffee or milk in winter. These changes that we observe show the change of seasons.
The seasons and changes in weather occur because earth rotates on its fixed axis. Changing seasons are almost periodic in nature.
Changes that do not repeat themselves after a definite interval of time and occur randomly are called non-periodic changes. Eruption of a volcano, occurrence of an earthquake, a streak of lighting flash across the sky during a thunderstorm, running of a batsman between the wickets, movement of legs while dancing are a few examples of non-periodic changes.