Churning of buttermilk | Centrifugal force pulls object away from center
We know that butter comes up when buttermilk is churned. There is a scientific principle behind the coming up of butter cream from the churning of butter milk. In rotatory motion, every object experiences two forces. One is the Centripetal force which pushes the object towards the center. Other is Centrifugal force which pulls the object away from the centre.
During the churning of buttermilk, many particles of curd undergo rotatory motion. Then the particles with less weight experience more centripetal force and hence those particles accumulate at the center. Heavier particles experience more centrifugal force and so they are forced to the walls of the container away from the centre. Hence, light butter particles accumulate at the center due to centripetal force and heavy buttermilk particles thrown away from the center to the walls of the container due to the centrifugal force. In this way butter cream gets separated from the butter milk. Similarly butter can also be taken from the raw milk using the similar procedure. Similar method is used to know the percentage of butter existing in the milk.