IO ANSWERS TO PRACTICAL QUESTIONS 



5. How deep is a well, if it takes three seconds for a stone to 

 fall to the bottom of it ? 



(2) equation of falling bodies, d = 1W ; hence d = 16 x 3 a a 144 feet. 



_6. Is the centre of gravity always within a body as ', for 

 example, a ring? 



It is not. In the case given it is at the centre of the circle. 



7. If two bodies, weighing respectively i and 4 pounds, be 

 connected by a rod 24 inches long, where is the centre of gravity ? 



To be In equilibrium the weight of one multiplied by its distance from the 

 c:nt-re of gravity must equal the weight of the other multiplied by its distance. 

 24 -+- 6 = 4 ; hence 4 in. is the unit for each pound. Therefore the centre of 

 gravity is 8 in. from the larger weight and 16 in. from the smaller. 



- 8. In a ball of equal density throughout, where is the centre 

 of gravity ? 



At the centre of the ball. 



9. Why does a ball roll down hill? 



Because the line of direction falls without the small base of the 

 ball. 



10. Why is it easier to roll a round body than a square one f 

 Because the base of the ball is so much smaller, and therefore 



the centre of gravity need not be raised to bring the line of di- 

 rection without. 



1 1. Why is it easier to tip over a load of hay than one of 

 stone ? 



Because the centre of gravity in a load of hay is very high, 

 and in a load of stone very low. Therefore the centre of 

 gravity in the former need not be raised much to bring the 

 line of direction without the base, while in the latter it must be. 



12. Why is a pyramid the stablest of structures ? 



Because the base is so broad and the centre of gravity so 

 low. The centre of gravity must therefore be lifted very high 

 before the line of direction will fall without the base. 



13. When a hammer is thrown, on which end does it always 

 strike f 



On the heavy end or head, because that part is attracted by 

 the earth more strongly. 



