CHAPTER IX 



CERTAIN MOVEMENTS IN MAN 

 From the Point of View of Dynamics 



Summary. — Object of dynamics — Measurement of the forces which 

 play a part in human locomotion— Traction dynamograph — 

 Dynamograph for expressing the amount of pressure exercised 

 by the feet on the ground— Combination of the dynamograph 

 with a method of recording movements — The laws of ballistics as 

 applied to the mechanism of jumping — Combined employment of 

 dynamograpliy and chronophotography— Mechanical work done 

 ill human locomotion; work in the vertical direction; work in 

 the horizontal direction; work done in maintaining the move- 

 ment of the lower limbs during their period of suspension — 

 Relative amount of work done during different kinds of paces 

 — Practical applications. 



The movement of a solid body, and the force which 

 produces it, are necessarily closely associated, so that 

 knowledge of movement implies knowledge of force, 

 and vice versa. At the same time, in practice it is 

 easier to measure force directly by means of the 

 dynamometer. 



Now, in human locomotion, the forces which are 

 concerned are ever variable quantities, and to thoroughly 

 understand each individual phase, a registering appa- 

 ratus which affords a continuous record must be em- 

 ployed. Such an apparatus is called a " dynamometer," 

 and indicates by the variations in its curve the amount 

 of force which acts upon it at any particular moment. 



Dynamometers are constructed on the principle that 



