430 



THE HUMAN MOTOR 



2. A journey, on the level, of about 3 kilometres. 



3. A total effort, by the muscles of the upper limbs, of 1,862 kg. 

 The work done by a subject weighing 70 kg. was : 



3,000 X 70 = 13 12 



This, foi a day of 10 hours, is 131,250 kgm. 



327. The use of the two-wheeled stone truck (cabrouet) requires 

 some attention. If the handles of the truck are held at the 

 proper height, the centre of gravity 

 of the load can be brought to lie 

 vertically above the axis of the 

 wheels. The labourer propelling 

 the truck has then only to over- 

 come the fractional resistances of 

 the ground and the wheels (fig. 

 289). If, however, this is not the 

 case, the centre oi gravity will lie 

 in front of, or behind, the axis of 

 the wheels (vide fig. 290). If, foi 

 example, the centre of gravity of 

 the load lies behind the axis of the 

 wheels, at G 2 in fig. 291. the force 

 will act partly on the axis O and 

 partly on the arms of the labourer, and the " couple " will 



G! 



Fio. 2 



Position of the load on a 

 stone truck. 



o 



"o"" 1 "^ 



Fig. 290. Fig. 291. 



tend to turn the truck in the direction of the arrow. If, on the 

 other hand, the centre of gravity of the load is 

 in front of the axis, at G x the labourer will have to 

 exert a downward pressure on the handles of the 

 truck. 



On sloping ground the conditions will be further 

 modified. In fig. 292 let the centre of gravity G 

 of the load lie vertically above the axis O (the 

 inclined surface of the ground being shown by the 

 shaded line). The force P has a component V 

 at right angles to the surface of ground and 

 producing the friction therewith, which friction 



(*) The ratio of 1:16 between the metre-kilogramme and the kilogram- 

 metre is here made use of. 



FIG. 292 





