CENTER OF GRAVITY 



45 



10 IIoTf many cubic feet in a ton of gold ? 



11. How many cubic feet in two tons of anthracite coalf 



12. How many cubic feet in a ton of cork ? 



13. A fragment of metal lost 5 ounces when weighed in water ; what were its dlmen- 

 Eions, supposing a cubic foot of water to weigh 1 ,000 ounces ? 



Sobition: The loss of weight in water, 5 ounces, is the weight of a bulk of water equal 

 to that of the body. As we know the weight of a cubic foot of water, we can determine 

 the number of cubic inches or feet in any given weight, thus : as 1,000 (the weight of a cubic 

 foot of water in ounces) is to 5 ounces, so is 1,"2S (the number of cubic inches in a cubi« 

 foot) to 8.G4 cubic inches, the dimensions of the fragment. 



14. Wishing to ascertain the number of cubic inches in an irregular fragment of stone, 

 it was weighed in water, and its loss of weight observedto be 4.25 ounces. "What were its 

 dimensions ? 



SECTION III. 



CENTER OP GRAVITY. 



What is the 

 Center of Grav- 

 ity in a body ? 



Fig. 10. 



86. The Center of Gravity in a body, is 

 that point about which, if supported, the 

 whole body will balance itself. 



If we take a rod, or beam, of 

 equal size throughout, and suspend 

 it from the middle, Fig. 10, the 

 two sides will exactly balance each 



other, and it will remain at rest in 



a horizontal position. There being 

 as much matter similarly situated on one side of the support as on the other, 

 the force of attraction exerted on both sides will be alike, and therefore one 

 side can not overpower, or outweigh the other. 



In eveiy body, of whatever size or form, a point may be 

 found, about which, if supported, all the parts of the body will 

 balance, or remain at rest. Every body may be considered as 

 made up of separate particles, each acted upon separately by- 

 gravity, but as by supporting this one point we support the 

 whole, as by lifting it we lift the whole, and as by stopping it 

 we cause the whole body to rest, the whole attraction excrtc-d 

 on the entire mass may be considered as concentrated at tins one point, and 

 tliis point we cidl the Cester of Gravity. 



87. The Center of Magnitude of a body, 

 is the central point of the bulk, or mass of the 

 body. 



88. When a body is of uniform density, the 

 Center of Gravity avIU coincide with its 

 center of magnitude ; but when one part of a 



body is composed of heavier materials than another part, 



now may we 



consider the 

 whole attrac- 

 tii>ii exerted on 

 a body concen- 

 trated at its 

 Center of Grav- 

 ity? 



What is the 



CenterofMag- 



nituda? 



Wliere is the 

 Center of Grav- 

 ity of a body ? 



