THE LEVER AND BALANCE 43 



attached a pointer, the end of which moves in front of an ivory scale, 

 fixed at the bottom of the upright which carries the beam. When not 

 in use, the beam and hooks are lifted off the knife edges by turning a 

 handle. 



FIG. 34. A simple balance, or pair of scales. 



QUESTIONS ON CHAPTER VIII. 



24. A uniform plank used as a see-saw is 16 feet long and weighs 90 Ibs. 

 Two boys, whose weights are 60 Ibs. and 100 Ibs. respectively, sit astride 

 it one foot from each end. Where must the plank be supported in order 

 that it may balance ? 



25. It is easier to balance a lever when weights are hung from it than 

 when the weights are placed on top of it. How do you explain this ? 



26. A scale whose length is a metre is balanced on a fulcrum at its centre. 

 A weight of 30 gm. is hung on the scale at 10 cm. from one end. Calculate 

 where each of the following weights should be hung in order to balance the 

 30 gm., namely, 40, 50, 60, 75, 80 gm. Point out the relation between the 

 weights and their distances from the fulcrum. What is the smallest weight 

 which you could use to balance the 30 gm. ? 



27. State the rules which you have been taught to observe in weighing 

 a body on a balance, and give reasons for them. 



28. Sketch and explain a simple apparatus for weighing bodies, making 

 use of only one known weight. 



29. Being given a metre scale and a known weight, show how these might 

 be employed to weigh bodies. 



30. A wooden lath used as a lever is first balanced on a fulcrum. On 

 one side of the fulcrum, 15 cm. from it, a weight of 42 gm. is then hung 

 from the lath, and on the other side of the fulcrum, 24 cm. from it, a weight 

 of 35 gm. is hung. 



Find whether the weights would or would not balance one another. 

 If they do not balance, find where the weight of 35 gm. must be hung from 

 the lath that the two weights may balance. 



