134 



CENTRE OF GRAVITY 



CH. IX 



Fig. 65. 



cause the centre of suspension and the centre of 

 gravity coincide. 



If we suspend it from some other point, A, we 

 find that the board will hang- steadily in one posi- 

 tion only, namely : when the centre of gravity is 

 vertically under the point of suspension. 



If we flatten one corner slightly, as shown in Fig. 

 65, we can make the board stand upon it, when G 

 is vertically above A, but it will be in 

 unstable equilibrium and will fall to 

 the rieht or left at the slightest touch. 

 We therefore say that the board is 

 in equilibrium when the centre of 

 gravity is vertically above the point 

 of support. Conversely, the centre 

 of gravity is vertically above the point of support 

 when the body is in equilibrium. 



Now, a coach, looked at from behind, is sym- 

 metrical as to the distribution of its parts about its 

 vertical centre line, and its centre of gravity must 

 be, therefore, somewhere in that cen- 

 tre line. If we tip the coach on the 

 two wheels of one side until it ex- 

 actly balances and would fall to either 

 side, the centre of gravity must be in 

 the vertical line passing through the 

 point of support. Since it is also in 

 the centre line of the coach, it must be at the inter- 

 section of these two lines, as shown in Fig. 66. 

 We can determine by this experiment the angle 



y/////////////////// 

 Fig. 66. 



