PHYSICAL SCIENCE
Physics Unit
Chapter 15 – Waves
Section 1 – Types of Waves
A. What is a Wave?
1. wave – periodic disturbance that carries energy through matter or space;
Fig. 1, p. 505, bottom
2. most waves travel through a medium; Fig. 2, p. 506, bottom
a. medium – physical environment in which phenomena occur
b. mechanical wave – waves that require a medium; almost all waves
3. electromagnetic wave – wave that consists of oscillating electric and magnetic
fields, which radiate outward at the speed of light; light does not require a medium;
Fig. 2, p. 506, bottom
4. waves transfer energy and can do work;
a. are able to exert a force over a certain distance
b. tsunami – huge ocean wave caused by earthquakes; may be as high as 30 meters;
carry enough energy to cause damage to coastal towns; Fig. 3, p. 507, top
c. energy of normal ocean waves breaks up rocks into pieces to form sandy beaches
5. energy may spread out as a wave travels
PS 15-1b
B. Vibrations and Waves
1. waves are related to vibrations; most are caused by a vibrating object
2. vibrations involve transformations of energy
a. mass hanging on a spring provides a good example
b. cycle of a mass hanging on a spring; Fig. 4, p. 508, bottom
c. simple harmonic motion – periodic motion which has a path formed by one or more
vibrations that are symmetric about an equilibrium position
3. wave can pass through a series of vibrating objects
a. disturbance that starts with first mass travels down the row; a wave that carries
energy from one end of the row to the other; Fig. 5, p. 509, top
b. damped harmonic motion – vibration that fades out as energy is transferred from
one object to another
4. motion of particles in a medium is like the motion of masses on springs
C. Transverse and Longitudinal Waves
1. transverse wave – waves in which the particles of the medium move perpendicular to the
direction the wave is traveling; Fig. 6, p. 511, bottom
a. crest – highest point of a wave; Fig. 8, p. 512, bottom
PS 15-1c
b. trough – lowest point of a wave
2. longitudinal wave – waves in which the particles of the medium vibrate parallel to the
direction of the wave motion; Fig. 7, p. 512, top
a. compression – point of highest density in a longitudinal wave; corresponds to crest;
Fig. 8, p. 512, bottom
b. rarefaction – portion of wave in which the density and pressure of the medium are at
a minimum; stretched out areas of a longitudinal wave; corresponds to trough
3. surface wave – wave that occurs at the boundary between two different mediums and in
which the particles move both perpendicularly and parallel to the direction that the
wave travels; Fig. 9, p. 513, top