122 Domestic Science 



performed. The energy possessed by the weight because 

 of its position is termed " Potential Energy ". As long 

 as the weight remains on the table, no work may be 

 done by it, but it can do a certain amount of work 

 during its fall. 



Suppose the weight to be on the table as before. 

 A nail may be placed in such a position that the weight 

 will strike the head of the nail if it be allowed to fall 

 from the table. On letting the weight fall, it will 

 drive the nail into the floor for a distance which will 

 depend on the nature of the floor and the sharpness 

 of the point of the nail. That is to say, the force 

 applied by the moving weight will overcome the 

 resistance offered by the material to the passage of 

 the nail, and the point of application of this force 

 the head of the nail will move a certain distance 

 in the direction of the line of action of the force, i.e. 

 vertically downwards. Thus work will be done. The 

 moving weight, at the instant of hitting the head of 

 the nail, evidently possesses energy by virtue of its 

 motion. Such energy is termed "Kinetic Energy". 



78. A few other examples of bodies possessing 

 potential energy are : 



(a) A bent bow. 



(b) A freshly wound watch-spring. 



(c) The weight of a Dutch clock while the clock 



is going. 



(d) The muscles of a runner about to start in 



a race. 



(e) The water in a mountain lake. 



(/) The coal stored in the bunkers of a ship. 



Exercise for Student. 



Try to account for the possession of potential energy by these 

 bodies by reasoning from what has been already stated. 



