EXPEEIMENTS ON THE LAWS OF MOTION. 53 



of translation. Every part of the weights has at any 

 instant the same velocity as every other ; but this is 

 not the case with every part of the wheel ; the velocity 

 of the particles at the circumference is greater than that 

 of the others, and it continually diminishes towards the 

 centre which is at rest. It follows from this, that less 

 force is required to give a certain velocity to the cir- 

 cumference of the wheel than would be necessary for 

 giving the same velocity to the whole mass of it. The 

 force actually required is only half of the force which 

 would give the velocity of the circumference to the 

 whole wheel. The weight of the wheel being 100 

 grammes, the force required is that which would com- 

 municate the same velocity to a weight of 50 grammes. 

 In the third experiment the total weight moved by 

 the action of gravity upon the extra weight of 6^ 

 is therefore not only 70 + 76 = 146^, but the wheel 

 must be included and reckoned as a weight of 50^. The 

 mass moved in this experiment was 50 + 70 + 76 

 = 196 gr , the moving force was 6 gr , and the space 

 traversed was 6 decimetres in 2 seconds. 



Fourth Experiment. A weight of 98 gr is now added at 

 each side. The whole mass moved is (50 + 70 + 98) 

 on the left, (70 + 98 + 4 + 1 -f 1) on the right, or 

 392 gr altogether. The moving force is still 6 gr , but the 

 mass moved is exactly twice that moved in the third 

 experiment. The plate will now have to be fixed at a 

 distance of three decimetres from the starting point, in 

 order to hear the extra weight strike it after two seconds. 

 Half the space only is now traversed in the same time. 



Fifth Experiment. New weights, again of 98 gr each, 

 are added to both sides. The moved mass is now 



