118 Domestic Science 



6. Explain why it is easier to sit on a horizontal bar than 

 to stand on it. 



7. For what reason are the legs of a three-legged stool spread 

 outwards ? (Note that the base of the stool, with respect to its 

 stability, is the figure formed by passing a piece of string around 

 the legs at the ground-level.) 



8. The centre of gravity of the moving parts of a chemical 

 balance is always situated at a point near and vertically below the 

 centre knife-edge. Why ? How would the balance be affected if 

 its centre of gravity were (a) exactly at the middle point of the centre 

 knife-edge; (6) at a point immediately over this middle point; 

 (c) at one side of the middle point ? 



CHAPTER VIII 



WORK, POWER, AND ENERGY. 

 THE NATURE OF HEAT 



73. In Chapter in a force was defined as that 

 which produces or tends to produce motion in a body. 

 If the force actually does produce motion, and the 

 point of application of the force moves in the direction 

 of its line of action, the force is said to do work on the 

 body. We measure the quantity of work done by 

 finding the product of the force and the distance through 

 which its point of application moves as described above. 

 Thus a man pushing a wheelbarrow along a garden 

 path is doing work on the wheelbarrow. The force 

 exerted in this case is the muscular force applied by 

 the man in a horizontal direction, its points of applica- 

 tion lie at the ends of the handles of the barrow, and the 

 distance through which the point of application moves in 



