- Editor H

# Physics and Math - 1. Introduction

Introduction

This appendix discusses selected aspects of **biophysics**, the study of physics as it applies to biological systems. Because living systems are in a continual exchange of force and energy, it is necessary to define these important concepts. According to the seventeenth-century scientist Sir Isaac Newton, a body at rest tends to stay at rest and a body in motion tends to continue moving in a straight line unless the body is acted upon by some force (Newton’s First Law).

Newton further defined **force** as an influence, measurable in both intensity and direction, that operates on a body in such a manner as to produce an alteration of its state of rest or motion. Put another way, force gives **energy** to a quantity, or mass, thereby enabling it to do work. In general, a driving force multiplied by a quantity yields energy or work. For example:

*force * distance = work*

Energy exists in two general forms: kinetic energy and potential energy. **Kinetic energy **{*kinein*, to move} is the energy possessed by a mass in motion. **Potential energy** is energy possessed by a mass because of its position. Kinetic energy (*KE*) is equal to one-half

the mass (*m*) of a body in motion multiplied by the square of the velocity (*v*) of the body:

*KE = 1/2 mv²*

Potential energy (*PE*) is equal to the mass (*m*) of a body multiplied by acceleration due to gravity (*g*) times the height (*h*) of the body above the earth’s surface:

*PE = mgh*, where *g* = 10 *m/s²*

Both kinetic and potential energy are measured in joules.

*Richard D. Hill and Daniel Biller University of Texas*