(ii)    Periodic and non-periodic changes
(a)      Periodic change :  A change which is repeated after regular intervals of time is called a periodic change.
        Swinging of a pendulum, rising and setting of the sun at a given place, and change of seasons are some examples of periodic changes.

(b)      Non periodic change : A changes which does not occur after regular intervals of time is called a non-periodic change. Most of the changes happening around us are non-periodic changes, occurrence of floods and cyclones are some of them.

(iii)    Desirable and undesirable changes
(a)      Desirable change : Some changes are beneficial for the mankind and we desire them to happen. Such changes are called desirable changes.
        eg. ripening of fruits, photosynthesis

(b)      Undesirable change : Some changes are harmful for us, and we need to stop them. Such changes are called undesirable changes.
        eg. Spoilage of food, rusting of iron.

(iv)    Natural and Man-Made changes
(a)     Natural  change  : A change that occurs naturally on its own is called a natural change.
        eg. changing of season, occurence of tides, eclipses.

(b)      Man-made  change  : A man-made change is the one that occurs because of human activities. 
        e.g. Changing the direction of flow of a river by building a dam.

(v)    Slow and Fast changes
(a)    Slow changes : Some changes take place at a slow rate, such changes are called slow changes.
        eg. Growth of plant, rusting of iron 
(b)    Fast changes : Some change take place in a fraction of second, such changes are called fast changes
        eg. Occurence of lightning during thunderstorm, earthquakes.