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# 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

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