110 Domestic Science 



Pass the hook through one of the holes in the rectangle, 

 and tie the other end of the thread to a nail fixed in 

 a drawing-board or other convenient wooden board. 

 Support the board in a vertical position so that the 

 rectangle hangs freely in front of it. Allow the figure 

 to come to rest. Mark on the surface of the millboard 

 the point at which the thread crosses the edge of the 

 figure and draw with a straight-edged ruler a line 

 from this point, through the centre of the hole, to the 

 opposite edge of the figure. Repeat these operations 

 with the hook in each of the other holes in turn. It 

 will be noted that the three lines drawn all pass through 

 one point, which in this case will be found to correspond 

 with the point of intersection of the diagonals of the 

 rectangle. 



In the above experiment two forces are acting 

 the pull of the thread upwards and the weight of the 

 millboard downwards. These two forces balance one 

 another, since the rectangle remains at rest. Now two 

 forces can only balance one another when their lines 

 of action are in one and the same straight line. (This 

 may be tested by displacing the rectangle, suspended 

 as above, to one side, so that the line of action of the 

 pull of the thread is no longer vertically upwards. 

 On releasing the rectangle, so that it is acted upon 

 by the two forces mentioned above, it will move from 

 its position of displacement and, after swinging for 

 a short time, will come to rest with the thread hanging 

 in a vertical direction, i.e. in the same direction as 

 that in which the force of gravity acts.) From the 

 above considerations it is clear that the weight of the 

 body acts in each case in directions which all pass 

 through a certain point. As stated previously, this 

 point is called the centre of gravity of the body. 



