154 THE REALITIES OF MODERN SCIENCE 



From equation (7) we see that the energy expended in 

 accelerating a body of mass m is mas. For as we may, 

 however, substitute v 2 /2 from the equation v 2 = 2as, 

 which was derived on page 135. Hence the energy due 

 to translation is mv 2 /2, where v is the velocity at the 

 moment of our consideration. This important relation is 

 entirely general and is applicable to moving molecules. 



