MECHANICS. 



[Lesson IX. 



other machines, what is gained in power, is 

 lost in time or velocity. 



105. T. What have we to overcome in 

 drawing a body up an inclined plane? 



P. Friction, and the gravity of the body, 

 which always tends to make it occupy the 

 lowest level. 



106. T. What do you mean by the gra- 

 dient of an inclined plane ? 



P. It is the proportion of the height to 

 its length, and therefore the gradient may 

 be said to be 1 in 100, or 1 in 50, as the 

 case may be. 



107. T. W r hat do you mean by the 

 gradient being 1 in 100, or 1 in 50 ? 



P. It signifies, that the road rises 1 

 foot in height, for every 100 or 50 of its 

 length, and therefore the additional load to 

 be impelled up the inclined plane, will be 

 the one-hundredth or fiftieth part of the 

 weight to be impelled. 



108. T. Can you give me some familiar 

 examples of the use of the inclined plane ? 



P. Yes ; the common chisel is an in- 

 clined plane, and the wood to be cut is 

 the resistance or power to be overcome. 

 Hatchets act in the same manner ; planks 

 placed in various positions for the purpose 



of wheeling barrows to heights, or rolling 

 hogsheads to or from heights ; ladders 

 placed against houses or walls ; flights of 

 stairs ; some kinds of printing-presses ; 

 the shovel, and many other things are 

 familiar enough to most of us. 



109. T. Are not roads over hilly coun- 

 tries constructed on the principle of the 

 inclined plane ? 



P. Yes ; and when a road has to be 

 made to the top of a hill, it is usual to 

 make it either wind round the hill, or 

 ascend in a zigzag line. Carters usually 

 make their carts describe a zigzag line of 

 direction when ascending steep roads, 

 because it saves their horses expending too 

 much power. 



GENERAL QUESTIONS ON LESSON VIII. 



1. Are inclined planes always fixed ? 



2. Describe an inclined plane. 



3. Are inclined planes advantageous or 

 not? 



4. Why do we use inclined planes ? 



5. In using the inclined plane, what 

 have we to overcome ? 



6. Give some familiar examples of the 

 inclined plane. 



LESSON IX. 



IN our last lesson we considered the inclined plane as a fixed body; we have now to 

 regard it in the condition of a movable body, or movable inclined plane. When we 

 considered the inclined plane as a fixed body, the load or weight was movable ; but in 

 the present case we shall find that the load or resistance is fixed, and the inclined plane 



movable. In Fig. 31 you will see that we 

 have an inclined plane (i, p), with a heavy 

 weight (w) resting upon its small end (B). 

 This will illustrate the double capacity of 

 the inclined plane. For example, [Experi- 

 ment 5,] if we drag the weight up the 

 inclined plane by means of a cord, which is 

 represented by the dotted line, we raise the 

 weight from the level of B, c, to the height A. [Experiment 6.] We will now reverse 

 the thing, and move the inclined plane by pushing it under the weight, and you now 

 see we have moved the inclined plane through the space c, B, and the weight has been 

 raised through the height c, A. In the former experiment it acts as an inclined plane ; 

 in the latter experiment it acts as a wedge. 



