44 APPLIED SCIENCE 



43. The Wedge. A combination of two inclined planes 

 joined at their bases is called a wedge. This simple machine is 

 used to split wood, rocks, etc., and to raise heavy weights short 



distances. The power of the wedge cannot 

 be accurately estimated, as the force, number 

 of blows, and incline all have to be taken into 

 account. In splitting wood (Fig. 27), the 

 sides of the opening in the log act as levers, 

 and thus force the mass apart in advance 

 of the point of the wedge. More power is 

 gained by striking the head of the wedge 

 with either a small or a large hammer, than 



FIG. 27. Wedge, by pressure, as the momentum of the blow 

 tends to shake the particles of matter and 



cause them to separate. 



The lifting power of the wedge is utilized in dockyards, where 

 large vessels are raised by its agency. The heads of hammers are 

 fastened on by wedges driven in at the part of the handles near 

 the heads. Nails, knives, needles, razors, hatchets, chisels all 

 act on the principle of wedges. A saw in motion represents a series 

 of wedges which are drawn along and pressed on the object to be 

 cut. When the edge of a razor is examined by a microscope, it 

 is seen to be sawlike in formation; by being drawn along the 

 beard, it cuts off the hairs. 



44. Application of the Principle of the Wedge. Just as 

 the power of the inclined plane is proportional to the height 

 and length of the plane, so is the power or force applied to 

 the wedge proportional to its height and length. In this 

 latter case, however, the length is the horizontal length or 

 base ac (Fig. 28) and not the sloping face bg. By the prin- 

 ciples of similar triangles, we can easily prove that when a 

 force acts in a direction parallel to the base of a wedge, the 



