Waves and Sound Feel the Beat….

Mechanical Waves Require a medium to travel. Transverse, Longitudinal, Surface

Wave Description Frequency Unit Equation How frequently a wave pulse occurs. Unit Hertz (Hz) 1 Hz = 1/seconds or s-1 Equation  

Wave Description Period Equation The time (in seconds) that it takes for one wave to pass. Equation T = Period (in seconds)  

Wave Description Frequency and Period are Inversely Related    

Types of Waves Transverse Waves Matter moves perpendicular to the direction of wave movement.

Types of Waves Longitudinal Waves Matter moves parallel to the direction of wave movement.

In the standing wave shown, what is the amplitude? In the standing wave shown, what is its wavelength? In the standing wave shown, how many nodes are there?

Key Principles Transverse wave particles vibrate perpendicular to the wave direction and longitudinal wave particles vibrate parallel to the direction of the wave propagation. Sound waves are mechanical longitudinal waves. Light waves are electromagnetic transverse waves. The speed of a wave depends only on the properties of the medium. The energy of a wave is directly proportional to the square of the amplitude. Superposition Principle: When two or more waves exist simultaneously in the same medium, the resultant amplitude at any point is the algebraic sum of the amplitudes of each wave.

Key Formulas

Wave Encounters When a wave meets an object 4 things could happen Reflection – wave bounces in new direction Refraction – wave bends as it passes thru Diffraction – wave bends as it passes around Absorption – wave is absorbed and disappears

Superposition Principle Constructive vs destructive Moving waves allow for this to change as the wave moves

Key Principles - Sound The speed of a wave depends only on the properties of the medium. The intensity of sound is inversely proportional to the distance. The harmonics produced in open pipes are similar to those produced in strings. The fundamental occurs when the length of the pipe (or string) equals 1/2 λ. The fundamental on a closed pipe occurs when the length of the pipe equals 1/4 λ. Only the odd harmonics are possible for a closed pipe. Whenever two waves exist simultaneously in the same medium and they are nearly at the same frequency, beats are set up. Doppler effect is the apparent change in frequency of a source of sound when there is relative motion of the source and the listener.

Key Formulas

vsolids > vliquids > vgases Wave Speed Speed of sound is determined only by the medium it travels through. The closer the molecules are, the faster it travels. Sound travels fastest through solid vsolids > vliquids > vgases Slower than sound is subsonic Faster than sound is supersonic Material Sound Speed Air 330 Helium 965 Water 1530 Wood 2000 Gold 3240 Steel 5940

Sound Wave Properties Pitch is determined by frequency Most sound waves have multiple frequencies – timbre Energy determines loudness of the sound Intensity decreases as the wave moves away from the source Loudness measured in decibels

Intensity Scales Examples Hearing threshhold 0 dB Whisper 20 dB 102X Ordinary talk 60 dB 106X Jackhammer 90 dB 109X IPOD Maxed 100 dB 1010X Front Row Concert 110 dB 1011X Pain Threshold 130 dB 1013X

Doppler Effect Effect of moving objects and sound waves Sound waves get closer together as the source approaches Sound waves spread out as the source goes away

Resonance Every wave has a natural frequency Constructive interference increases energy causing resonance Increased amplitude = increased energy

Harmonics Almost all sounds are a mix of various frequencies – harmonics. Different mixes can produce the same overall frequency but a slightly different sound….

Developing the harmony

Creating a sound…