76 ENERGY. 



of a Pendulum ; Laws and Formulas for the Pen- 

 dulum ; the Cycloidal Pendulum ; the Second's 

 Pendulum ; the Use of the Pendulum in Clock- 

 work; Compensation Pendulums. 



V. 



ENERGY, 



150. Work. This is a world of work, a world in 

 which the necessity of working is imposed upon every 

 living creature. If a man is poor, he must work for the 

 means of living; if he is rich, still he must work to live. 

 But in physical science, the term worTc has a broader 

 meaning, and signifies the overcoming of resistance 

 of any kind. Whether this overcoming of resistance is 

 pleasant or not does not enter into consideration here, all 

 play being a species of work. The word is here used in 

 this enlarged, technical sense. 



151. Energy. Energy is the power of doing 

 work. If one man can do more work than another, he 

 has more energy. If a horse can do more work, in a given 

 time, than a man, the horse has more energy than the man. 

 If a steam-engine can do more work than a horse, it has 

 more energy. If a moving cannon-ball can overcome a 

 greater resistance than a base-ball it has more energy. 



152. Elements of Work Measure. Imagine a 

 flight of stairs, each step having a rise of twelve inches. 

 On the floor at the foot of the stairs are two weights, of 



