CENTRIFUGAL FORCE. 119 



quite different, however, in creaming milk in centrifugal separators, 

 for in this case the force can be regulated at will within compara- 

 tively wide limits. In such a method, the aim is to separate the 

 largest possible amount of the fat, by centrifugal action, which is 

 much more powerful than the force of gravity, and which in the 

 older methods, depending on the force of gravity, was not obtainable. 

 An accurate indication of how far this is effected is furnished by the 

 percentage of fat present in the skim-milk. The creaming coefficient 

 is not an indication of this. 



54. Centrifugal Force. One of the common properties of matter 

 is its inertia. This is manifested in a body by the opposition it 

 offers to any change in its motion. Any such change must be 

 effected by force. Inertia acts in such a way, that a body set in 

 motion tends to maintain the direction of its motion unchanged, i.e. 

 in a straight line. If a body is forced to move in a circle, in every 

 point of its movement it manifests a tendency to move at a tangent 

 to each point of the circle. The direction, therefore, to which it 

 tends to go has to be changed from point to point. The force 

 which effects this is known in physics as centripetal force. It is 

 produced when a body is swung round in a circle at the end of a 

 string by the tenacity of the thread, and in the case of a liquid 

 being put in circular motion in a vessel by the sides of the contain- 

 ing vessel. Since every force requires a counter force, a force 

 which acts in exactly similar but opposite direction, every body 

 moving in a circle is subjected to a force which moves from the 

 centre in the direction of the circumference along the radius, a force 

 exactly similar in its manifestation to the centripetal force. This 

 force is called the centrifugal force. The centrifugal force is the 

 force which overcomes the inertia of the material, and represents 

 the resistance offered by a body in motion, to change in its direction 

 of movement, and acts upon every body, moving in a curve, that is, 

 in a line, the direction of which changes from point to point. In 

 6 the acceleration 0, which the fatty globules experience when they 

 are subjected to the action of centrifugal force, was shown to be 

 capable of being calculated as follows: 



In which a L indicates the factor, representing the inertia, 8 and 8 1 

 the viscosity of the milk-serurn, and the butter- fat; n the Ludolph 



