Pure substances made up of two or more elements combined in fixed ratio is called a compound. The compound can be split into its constituent elements by chemical methods, and also they have a different set of properties than its constituent elements. Water, carbon dioxide, sugar are some examples of it.

The process of separating heavier and lighter components of a mixture by wind or by blowing air is called winnowing. This method is used by farmers to separate lighter husk particles from heavier seeds of grain. For example, wheat is separated from husk by using the winnowing method. Wheat and husk mixture is allowed to fall from a height. Husk being lighter than wheat grains gets separated from wheat because of wind or air blowing. Dirt particles can be removed from grains by winnowing.