38 SOME PHYSICAL FORCES EXEMPLIFIED IN MAN 



may result. These facts are the physical basis of the salt-free diets and other 

 chemical attempts to control water balance. 



ELECTRICAL FORCES 



Electrostatic Force 



Like the gravitational and osmotic forces, we know little about the nature 

 of electrical and magnetic forces either, but we can go a long way by study- 

 ing and applying their effects. 



The basic concept of electrostatics is that of the potential, ^ (psi), at a 

 point. The potential is defined as the work required (hence it is an energy) 

 to bring one positive charge from an infinite distance and place it at the 

 point or position in question. The unit of potential is, therefore, joules/ 

 coulomb. 



Potential itself is impossible to measure, but differences in potential can be 

 measured very accurately by the work they can do in the field or volume of 

 space in which they exist — work of repulsion of pith balls, for example, or 

 the work involved in deflecting the needle of a voltmeter or driving electric 

 charges through some closed circuit. The potential difference, ^ 2 - ^ 

 between two points is usually called " Fjou/cou, or volts." 



The term "charge" should be amplified. It is the quantity or amount of 

 electricity in a bundle — whatever electricity is. We know there are, for- 

 mally, two kinds of electrical charge; they are called positive and negative. 



