MEASUREMENTS 305 



R x D = T = 2Fd. 



So that, knowing T or R, we can deduce the value of the average 

 pressure F on the pedals. A value of R, sufficiently accurate 

 for practical purposes, is given by the equation : 



R = 0-012P + 0-0738SV 2 , 



P being the total weight of the bicycle and the rider, S the surface 

 area of the latter, about 0-60 sq. metres and V the speed in 

 metres per second. 



If the slope is inclined by * per metre : 



R = P (0-012 *) + 0-073SV 2 . 



Example : A speed of 18 kilometres an hour is maintained on 

 a slope where i 0-02 metre ; the bicycle weighs 15 kilogrammes 

 and the rider 65 kilogrammes. 



Then P = 65 + 15 = 80 kilogrammes. 



18,000 



V = = 5 metres per second. 



Therefore : 



R = 80 X 0-032 -f 0'073 X 0-6 x 5 x 5 = 3-655 kilogrammes. 

 The work done will be 



Per hour : 



3-655 X 18,000 = 65,790 kilogrammetres. 

 Per metre : 



10 ' A = 3-655 kilogrammetres. 



lo,UUU 



In the descent the value of R will be : 

 R = 80 X ( 0-008) + 0-073 x 0-6 x 5 x 5 = 0-455 kilo- 



grammes. 



Of course the nature of the ground, and the state of the tyres 

 will modify the preceding values. 



The ordinary work of the legs is that of locomotion (see below, 

 26S) ; they then support the weight of the human body with 

 variations depending on the nature of the movement. They 

 often have to resist, in addition, the weight of loads carried, 

 whilst displacing this total weight on the horizontal or on a slope. 

 The useful work is obviously the product of the weight displaced 

 by the sum of the amplitudes of the vertical oscillation of the 

 body walking on level ground, or by that sum increased by the 

 total slope that has been climbed.. But the horizontal journey 

 modifies the expenditure of energy to such an extent for a similar 

 amount of mechanical work that it is advantageous to use as 

 Coulomb did, a unit other than the kilogrammetre, one which 



