PAPERS ON CHEMISTRY AND PHYSICS 



141 



A LABORATORY EXPERIMENT FOR TESTING 

 THE EFFICIENCY OF A SCREW JACK 



A. P. Carmen axd R. F. Paton, Univebsity of Illinois 



Our object in devising this experiment has been to get 

 a feasible quantitative college experiment which would 

 fix the principle of work and the concept of efficiency of 

 a machine. "We chose as the machine a small screw jack, 

 the particular jack being an inexpensive one used to lift 

 light weight automobiles. The apparatus is shown in 

 s. 1 and 2. The hand lever was removed from the gear 



Fig. 1 



Fig. 2 



wheel of the jack and a disk was substituted. The 

 " power" force is applied as a weight hung by a wire cord 

 which is wound in a groove on the periphery of the disk. 

 This applies a moment of force to the small gear wheel 



