n8 ELEMENTARY SCIENCE 



it is either transmitted to some other body or transformed 

 into some other form. 



Take the case of the windlass and the well-bucket (see 

 P a g e 55)- Suppose, by winding, you have raised the 

 full bucket up to the axle on which the rope is wound. 

 The energy you expended hi pushing the handle of the 

 windlass is now transmitted to the full bucket at the top 

 of the well. The elevated position of the water in that 

 bucket, as compared with the water in the well from which 

 it came, is an investment of energy. All you have to do to 

 prove this is to drop the bucket. What happens ? Down 

 it plunges, and round and round the handle of the windlass 

 spins, far faster than you turned it in the opposite direc- 

 tion. Thus the energy which was transmitted to the 

 full bucket by the winding of the handle is rapidly trans- 

 mitted back again whence it came. Part of it is expended 

 in the force by which the axle unwinds, and part of it in 

 the force with which the bucket hits the surface of the 

 water in the well. 



Two Kinds of Energy. Here evidently are two kinds 

 of energy. The full well-bucket at the edge of the curb 

 had energy because of its elevated position. The handle, 

 when you were turning it, had energy because of its motion. 

 Energy possessed by a body because of its position or 

 condition is called latent or potential energy. Energy 

 possessed by a body because of its motion is called kinetic 

 energy. The former may be readily changed to the latter, 

 as when you dropped the bucket from the brim of the well. 

 A brick at the top of a building possesses an amount of 

 potential energy directly proportional to its weight and 

 its height above the surface of the earth. If the brick 



