SCIENCE OF COMMON THINGS. 



IT 



Stability of buildings. 



Centre of gravity in walking. 



Hence, tlie broader the base of a body, the more securely 

 it will stand. 



Thus, in Fig. 3, the line directed vertically from the centre of gravity, 

 G, falls within the base of the body, and it remains standing ; but in Fig. 

 4 a similar line falls without the base, and the body consequently cannot 

 be maintained in an upright position, and must fall. 



96 How long will a watt or tower stand securely ? 



So long as the perpendicular line drawn through its 

 eentre of gravity falls within its base. 



The celebrated leaning tower 

 pf Pisa, 315 feet high, which 

 inclines 12 feet from a per- 

 fectly upright position, is an 

 example of this principle. For 

 instance, the line in Fig. 5, 

 falling from the top of the 

 tower to the ground, and pass- 

 ing through the centre of gra- 

 vity, falls within the base, and 

 the tower stands securely. If, 

 however, an attempt had been 

 made to build the tower a lit- 

 tle higher, so that the perpen- 

 dicular line passing through 

 the centre of gravity would 

 have fallen beyond the base, 

 the structure could no longer 

 have supported itself. 



Fig.5. 



7* What is the advantage of turning out the toes when we walk f 



It increases the breadth of the base supporting the 

 body, and enables us to stand more securely. 



98 Why do very fat people throw hack their head and shoulders when 

 they walk ? 



In order that they may effectually keep the centre 

 of gravity of the body over the base formed by the 

 soles of the feet. 



99 W?cy cannot a man, standing with his heels close to a perpendicular 

 watt, bend over sufficiently to pick up any object that lies before him on the 

 ground, without falling ? 



Because the wall prevents him from throwing part 

 of his body backward, to counterbalance the head and 

 that must project forward. 



