Characteristics of Waves Chapter 15 Notes Characteristics of Waves

Section 15.1 - What are waves? Wave - a disturbance that transfers energy from place to place (Remember, energy is the ability to do work.) Medium - material through which a wave travels (solid, liquid, gas) Mechanical waves – waves that require a medium through which to travel. Chapter 15

What are waves? (cont.) Waves travel through the medium, but do not carry the medium itself with them. Ducks pg 511. Waves crashing on beach do move medium due to shallow water Mechanical waves are created when a source of energy causes a medium to vibrate Vibration - repeated up-and-down or back-and-forth motion Chapter 15

2 Types of Waves Mechanical waves are classified by how they move. There are two types of mechanical waves: transverse waves and longitudinal waves. Transverse - waves that move the medium at right angles to the direction in which the waves are traveling. Example - long spring (label crest, trough and amplitude) Longitudinal (Compression) - waves that move the particles of the medium parallel to the direction in which the waves are traveling. Example – slinky (label compressions and rarefactions) (Surface - Combinations of transverse and longitudinal waves. Example - waves on surface of the ocean) Chapter 15

Section 15.2 - Properties of Waves The basic properties of waves are amplitude, wavelength, frequency, and speed. Amplitude - maximum distance the particles of the medium carrying the wave move away from their rest positions. Transverse wave – amplitude is maximum distance up or down from its rest position. Longitudinal wave – amplitude is how comnpressed or rarefied the medium becomes. Chapter 15

Section 15.2 - Properties of Waves Wavelength - The distance between two corresponding parts of a wave (crest to crest, trough to trough) Transverse – distance from trought to trough or crest to crest Longitudinal – distance between compressions Frequency - The number of complete waves that pass a given point in a certain amount of time. Measured in hertz (Hz) cycles/sec. Chapter 15

Properties of Waves (cont.) Wave diagrams page 518 Speed - How far the wave travels in one unit of time Speed = Wavelength  Frequency Frequency = Speed / Wavelength Wavelength = Speed / Frequency Math Sample Problems pg.519 Chapter 15

Section 15.3 - Interactions of Waves Reflection - When a wave hits a surface through which it cannot pass, it bounces back. Law of relection Angle of incidence = angle of reflection (diagram pg.522) Demo - bounce ball off wall Chapter 15

Interactions of Waves (cont.) Refraction - When a wave enters a new medium at an angle, one side of the wave changes speed before the other side, which causes the wave to bend. Example - shopping cart wheel in water, light in water in pool, troops marching in mud Diffraction - When a wave moves around a barrier or through an opening in a barrier, it bends and spreads out Photos on page 524 Chapter 15

Interactions of Waves (cont.) Interference – the interaction between waves that meet. There are two types. Constructive interference - two waves combine to make a wave with larger amplitude Destructive interference - two waves combine to make a wave with a smaller amplitude Example - use slinky for constructive and destructive interference Chapter 15

Interactions of Waves (cont.) Standing wave - If the incoming wave and a reflected wave have just the right frequency, they produce a combined wave that appears to be standing still. (wave appears not to move) nodes - locations of zero amplitude antinodes - locations of maximum amplitude Demo - spring Resonance – an increase in the amplitude of a vibration that occurs when external vibrations match the object’s natural frequency Example - child on swing Chapter 15

Section 15.4 - Seismic Waves When the stress in rock builds up enough, the rock breaks or changes shape, releasing energy in the form of waves or vibrations. Seismic waves – waves produced by earthquakes. Three types of seismic waves: P waves - (Primary waves) longitudinal waves (compressions and rarefactions). Fastest seismic waves. Travel through all parts of the earth. S waves - (Secondary waves) transverse waves. Cannot travel through liquid (earth’s core) Surface waves – P and S waves reach the surface, combination of longitudinal and transverse waves. Move slower than P or S waves. Produce the most severe ground movements. Chapter 15

Seismic Waves (cont.) Tsunami – (huge) surface waves on the ocean caused by underwater earthquakes. Seismograph - device that records the ground movements caused by seismic waves as they move through the earth to detect and measure earthquakes Chapter 15