PHYSICAL FORCE MAN'S SERVANT 

 OR HIS MASTER? 1 



THE words "physical force" in my title probably 

 convey to you the correct notion of what is the main 

 subject of my address without any further explana- 

 tion. As a matter of fact, the term "force," in a 

 strictly scientific sense, is slightly different from that 

 in which it is popularly employed. The word in the 

 title is to be taken in its popular meaning 1 , which is 

 not the passive force or pressure exerted, for example, 

 by a column supporting a roof, but force actively at 

 work, moving something against a resistance ; or, if 

 passive, like the force of a coiled spring, or of an 

 explosive, waiting, as it were, the opportunity to 

 become active and do work. In scientific language 

 energy is the term now used to signify what once 

 was, and still is, popularly called force. Energy is 

 the power of doing work (kinetic energy), or anything 

 which can be converted into work (potential energy). 

 When a gun is fired, for example, the potential 

 energy of the explosive is converted into the kinetic 

 energy of the bullet, and this bullet possesses then 

 the power of doing work, of moving itself against a 

 resistance the resistance of the air and the resistance 

 of the target it strikes. 



In ordinary language physical force is often 

 referred to as "brute force," but science does not 



1 Address to the Independent Labour Party, Aberdeen, i;th 

 November 1915. 

 36 



