Chapter 11 and Chapter 12-7,8 Waves © 2014 Pearson Education, Inc. Info in red font is extra explanation and examples and is probably not necessary to write

Waves © 2014 Pearson Education, Inc. Big Idea 6: A wave is a traveling disturbance that can transfer energy and momentum from one location to another without the permanent transfer of mass and serve as a mathematical description of other phenomena A wave travels along its medium, but the individual particles just move up and down.

Wave characteristics: Amplitude, A Wavelength, λ Frequency f - number of waves per second Period T - time for one wavelength to occur Wave velocity: λ = v/f

Types of Waves Mechanical waves – a wave that must travel through a medium Electromagnetic waves (light) – waves that can travel through space Pulse wave – a single disturbance Periodic wave – a periodic disturbance Sine wave – a wave that’s source vibrates with simple harmonic motion

Transverse Waves – a wave whose particles vibrate perpendicular to the motion of the wave – Crest –highest point of the wave above the equilibrium – Trough –lowest point below the equilibrium – Wavelength – the distance between two similar points Equilibrium

Longitudinal waves – a wave whose particles vibrate parallel to the motion of the wave – Compression –particles are close to each other – Rarefaction –particles are far from each other – Wavelength – the distance between two compressions

Sound waves are longitudinal waves: Seismic Waves: Earthquakes produce both longitudinal and transverse waves, plus a 3 rd kind called surface waves A water wave is technically a surface wave because it is on the boundary between two different media. Particles of surface waves have circular or elliptical motion.

Wave Dimensions – how many dimensions does the energy travel in

Energy Transported by Waves The energy carried by a wave depends on and increases with amplitude. The energy and intensity (power of wave) increase with amplitude and the frequency Inverse square law: Due to damping, intensity decreases as the inverse square of the distance, r from the source Amplitude also decreases with distance from damping (substitute in A 2 for I) © 2014 Pearson Education, Inc. f2f2

Wave Front Diagrams © 2014 Pearson Education, Inc. 2D and 3D waves can be represented by wave fronts Lines perpendicular to the wave fronts are called rays; they point in the direction of propagation of the wave.

© 2014 Pearson Education, Inc. Refraction: If the wave enters a medium where the wave speed is different, it will be refracted—its wave fronts and rays will change direction. Law of Reflection: If a wave comes in at an angle (the angle of incidence) it will be reflected at that same angle Wave Behaviors

© 2014 Pearson Education, Inc. More Reflection: A wave hitting an obstacle will be reflected (diagram a with fixed rope), and its reflection will be inverted due to equal and opposite forces. A wave reaching the end of its medium, but where the medium is still free to move, will be reflected (b with free end of rope), and its reflection will be upright. Change of Medium: A wave going into a denser medium will be partly reflected and partly transmitted and speed may change

© 2014 Pearson Education, Inc. Interference – when two waves pass through the same space and time The Principle of Superposition - when two waves cross, they travel through each other and the resulting displacement is determined by adding the 2 wave displacements

© 2014 Pearson Education, Inc. Destructive interference – when two or more waves cancel each other out to create a smaller or nonexistent wave (out of phase) Constructive interference – when two or more waves add together to create a larger wave (in phase)

Doppler Effect The observed frequency of a wave depends on the relative motion of the source and the observer. © 2014 Pearson Education, Inc. A source moving toward an observer has a higher f and shorter λ; opposite when source is moving away. Also occurs with a fixed source and moving observer Pitch getting higher Pitch getting lower Pitch getting higher

Doppler radar – use Doppler effect to locate and track speed of storm Radar guns – use Doppler effect to get speed of car Redshift – use Doppler effect and fact that red light is the lowest frequency light wave to determine that galaxies are moving away from us – expanding universe from Big Bang © 2014 Pearson Education, Inc.

Shock Waves and the Sonic Boom If a wave source is moving faster than the wave speed, waves cannot keep up and a shock wave is formed. a)Source not moving, f not altered b)Source moving less than speed of wave, f altered according to Doppler effect c)Source and wave speed are equal, wave fronts pile up in front of source, f is altered d)Source moving faster than wave, wave crests overlap to create one large wave (same as boat in water) © 2014 Pearson Education, Inc.

Aircraft exceeding the speed of sound in air will produce two sonic booms, one from the front and one from the tail.