404 THE HUMAN MOTOR 



less Hubert recognised that with a light hammer, such as that 

 used by a nail-maker, a production of work, of as much as 160,000 

 kilogrammetres per diem might be attained. 



Gilbreth noted that the weight of the hammer was an import- 

 ant matter in the work of the stone mason. In splitting blocks 

 of granite a hammer weighing 12 kg. would effect as much in 5 

 blows as a hammer of 5 kg. could effect in a hundred strokes. 



Each trade needs an appropriate weight and shape of hammer. 

 A carpenter's hammer weighs about -55 kg. and has a handle 

 about half a metre long. The work of the smith necessitates a 

 very heavy implement (41). The rapidity with which the 

 hammer is used varies also in different trades. For example, 

 a carpenter driving stakes into the ground will deliver about 

 (JO blows per minute, his arm describing a semi-circle at a peri- 

 pheral speed of about 7-5 metres per second. The corresponding 

 expenditure of energy will be : 



* mv * = i Hi!? 7 ' 52 = 15 ' 75 k S m - 



For double oscillation of the hammer it will be 31-50 kgm. 



If a workman drives 350 stakes per diem, he will deliver 

 350 X 11 blows of the hammer, at 11 strokes per stake. The 

 total work done will be : 



31-50 X 11 X 350 = 121,276 kilogrammetres. 



If the small accessory operations are added to this, such as the 

 effect of the 350 X 11 = 3,850 oscillations of the arm^ 1 ) the total 

 muscular action will be about 130,000 kilogrammetres a day. 



310. The Use of the File. This operation in metal working has 

 received special attention. ( 2 ) The workman must exert both a 

 downward pressure, in order that the teeth of the file may obtain 

 a bite on the metal, and also the horizontal effort needed to tra- 

 verse the file over the work at the required speed. The general 

 conditions which will be found by an analysis of the operation, are 

 as follows (see fig. 276) . 



The efforts of both arms have horizontal and vertical com- 

 ponents, V V' and H H' respectively. The vertical components 

 keep the file down on the work, while the horizontal components 

 drive the file and, properly speaking, do the actual work. 



() The moment of inertia of the upper limb being 0'03, it is calculated 

 that about 0'60 kgm. of work is done at each oscillation, or altogether 

 3,850 X 0-6 = 2,310 kilogrammetres. 



( 2 ) Jules Amar (Journal de Physiol., Jan., 1913, p. 62 ; Comptes Rendus 

 Acad. Sciences, Nov., 1912). 



