Chapter 8.2 Chapter 8.2 NotesNotes

Wave Wave InteractionsInteractions

When 2 or more waves of the When 2 or more waves of the same type are combined at same type are combined at the same place at the same the same place at the same time, the result is time, the result is interferenceinterference..

When two waves combine When two waves combine and produce a larger wave, and produce a larger wave, this is called this is called constructiveconstructive interference.interference.

When two waves combine When two waves combine and produce a smaller and produce a smaller wave, this is called wave, this is called destructivedestructive interference. interference.

The principle of adding The principle of adding displacements of displacements of overlapping waves is overlapping waves is called the principle of called the principle of superpositionsuperposition..

When a wave is reflected it When a wave is reflected it changes changes directiondirection..

If a rope is tied to a wall If a rope is tied to a wall and a wave is created that and a wave is created that is heading towards the is heading towards the wall, when the wave hits wall, when the wave hits the wall it will change the wall it will change directiondirection..

The reflected wave The reflected wave changes direction but the changes direction but the wavelength does not wavelength does not changechange..

The reflected wave is also The reflected wave is also invertedinverted; A crest ; A crest becomes a becomes a troughtrough and a and a trough becomes a trough becomes a crestcrest..

StandingStanding waves are waves that waves are waves that are a result of reflections of waves are a result of reflections of waves that are constantly being reflected that are constantly being reflected and interfering with each other.and interfering with each other.For example, when guitar strings For example, when guitar strings are plucked, the waves created are are plucked, the waves created are reflected back and forth on the reflected back and forth on the strings and are constantly strings and are constantly interferinginterfering with each other. with each other.There is one point in the string or There is one point in the string or on a wave that is stationary called on a wave that is stationary called the the nodenode..

When two waves interfere When two waves interfere with each other and produce with each other and produce a larger wave in constructive a larger wave in constructive interference the waves are interference the waves are said to be said to be in phasein phase..

When two waves interfere When two waves interfere with each other and produce with each other and produce a smaller wave in destructive a smaller wave in destructive interference the waves are interference the waves are said to be said to be out of phaseout of phase..

When two sources of sound waves When two sources of sound waves that are nearly in the same that are nearly in the same frequency will interfere with each frequency will interfere with each other and produce other and produce beatsbeats which are which are variations in loudness.variations in loudness.

The The natural frequencynatural frequency of an of an object is a single frequency at object is a single frequency at which the object vibrates in nature. which the object vibrates in nature. Example is a pendulum or a Example is a pendulum or a vibrating spring. It will always vibrating spring. It will always swing or vibrate at the same swing or vibrate at the same frequency.frequency.

Beats DemoBeats Demo

Force VibrationForce Vibration is when an is when an object is forced to vibrate at object is forced to vibrate at the frequency of the force.the frequency of the force.

When the forced vibration of When the forced vibration of an object matches its natural an object matches its natural frequency, it causes the frequency, it causes the object to have an increased object to have an increased amplitude. This is called amplitude. This is called resonanceresonance..

Wine Glass Forced VibrationWine Glass Forced Vibration

Resonance DemosResonance DemosChinese Spouting BowlChinese Spouting Bowl

Tibetan BowlTibetan Bowl

PVP PipesPVP Pipes

Iron TubeIron Tube

Imagine you’re sitting on a Imagine you’re sitting on a swing and want to go swing and want to go higher. You pump your legs higher. You pump your legs at a certain rate to increase at a certain rate to increase your swinging. This is an your swinging. This is an example of you creating example of you creating resonanceresonance by matching by matching the frequency of the swing.the frequency of the swing.