CHAPTER XXX 



DEFINITIONS AND PRINCIPLES 



A Tool. A tool is an instrument such as a hammer, fork, 

 or spade used in performing manual operations. Tools so 

 denned will not be discussed in this text. The term may be 

 used, perhaps incorrectly, to designate a machine or an imple- 

 ment. Machines for making hay, for instance, are some- 

 times called hay tools. 



Implements. The term implement is applied to both 

 tools and machines. A dealer in these wares is generally 

 known as an implement dealer. 



Machines. A machine is any device consisting of two 

 or more parts arranged to modify forces and motions, to 

 produce a desired effect or do some useful work. Machines 

 require energy from an outside source to drive or operate 

 them, and of this energy a part is "required to drive the 

 machine itself and a part is required to do the useful work. 

 As will be explained later this energy is generally designated 

 as work. The ratio between the work put to any useful end 

 and the total amount of work given to the machine is known 

 as the efficiency of a machine. For instance, suppose that 

 a certain machine, like a pump, requires one horsepower of 

 energy to operate it. Suppose that of this amount, one- 

 half horsepower is used in the actual lifting of the water 

 and the remainder is used in overcoming the friction in the 

 pump. Then the efficiency of the pump is 50 per cent. 



Elements of Machines. All machines, regardless of their 

 intricacy, may be reduced to the elements of machines, or 

 the simple machines, as they are called. These comprise 



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