HEALTH AND FOOD STANDARDS 91 



128. Units of energy. To measure the energy expended by 

 the body, or to measure anything else, we must have a unit. 

 We measure length in inches or yards or miles. In a similar 

 manner we are able to measure energy by ivork done. But as 

 different forms of energy do different kinds of work, it is 

 necessary to find some common unit for measuring. For 

 example, motion can be measured by the quantity of matter 

 moved and the distance through which it is moved, as one 

 ton raised five inches, three pounds raised two feet. The unit 

 of measuring this kind of work may be the foot pound, or the 

 amount of energy it takes to raise one pound of matter one foot. 



It takes a certain quantity of heat to change the temperature 

 of a pint of water from ordinary room temperature (about 18° C. 

 or about 65° F.) to the boiling point (212° F.). For a quart of 

 water it would take twice as much heat to do the required work. 

 As a unit of energy we might use, for example, the pint degree. 

 Among engineers the quantity of heat needed to raise one kilo- 

 gram of water (a little more than a quart) from the temperature 

 of 0° to the temperature of 1° C. is called a calorie. This unit 

 is sometimes called a "large calorie," to distinguish it from the 

 "small calorie" (i gram of water, one degree Centigrade), 

 which is used in very delicate measurements. 



In dealing with fuel or the conversion of fuel energy into other 

 forms, it is customary to record energy in terms of calories. In deal- 

 ing with mechanical work it is customary to record energ)' in terms of 

 foot pounds, or horse-power hours.^ 



From these figures it will be seen that a given quantity of fat contains more 

 than twice as much latent energy as the same quantity of protein or carbohy- 

 drate, and that the latter two classes of compounds have the same fuel value. 



