Chap. 2 



LIFE IS A CONCERN OF MATTER AND ENERGY 



11 



Fig. 2.1. Change from the potential energy of position to the kinetic energy of 

 motion in the threads of a mayfly egg, the size of a sand grain. Before the egg is laid 

 a wiry thread is coiled like a watch spring around each end of it; the energy in their 

 coils is potential. Mayflies strew their eggs on lakes and streams. As the eggs touch 

 the water the coils spring loose; in so doing their potential energy becomes kinetic. 

 The threads catch on submerged twigs and the eggs are suspended above the mud 

 that otherwise would smother them. 



respiration of every living cell is a chemical reaction in which the chemical 

 energy in the cell's substance is transformed into the energy of activity and 

 heat. 



Transformations of one kind of energy into another are constantly going on 

 about us. The radiant energy of the sun becomes that which is stored in the 

 simple sugars of green grass. Cows feed on grass and its stored energy is even- 

 tually transformed into milk for calves or babies. 



Atomic Energy. The energy within the atom shows itself in qualities of 

 cohesion. It is liberated when under special conditions one kind of matter is 

 changed into another, e.g., nitrogen into oxygen. Such a change generally 

 occurs in atoms in which the particles in the nucleus are numerous. They may 

 be unbalanced for a long period and relatively unstable as in radium, uranium, 

 and thorium. Such atoms cannot hold themselves together and their radio- 

 activity is a long, continued breaking apart. 



The beginnings of the knowledge of radioactivity moved rapidly. In 1895 

 Rontgen concluded that some active radiation emitted spontaneously from 



