Chapter 8.2 Notes Wave Interactions Wave Interactions

When 2 or more waves of the same type are combined at the same place at the same time, the result is interference. interference When two waves combine and produce a larger wave, this is called constructive interference.

When two waves combine and produce a smaller wave, this is called destructive interference. The principle of adding displacements of overlapping waves is called the principle of superposition.

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

The reflected wave changes direction but the wavelength does not change. The reflected wave is also inverted; A crest becomes a trough and a trough becomes a crest. inverted

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

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

When two sources of sound waves that are nearly in the same frequency will interfere with each other and produce beats which are variations in loudness. The natural frequency of an object is a single frequency at which the object vibrates in nature. Example is a pendulum or a vibrating spring. It will always swing or vibrate at the same frequency.

Beats Demo

Force Vibration Force Vibration is when an object is forced to vibrate at the frequency of the force. Force Vibration When the forced vibration of an object matches its natural frequency, it causes the object to have an increased amplitude. This is called resonance.

Wine Glass Forced Vibration

Resonance Demos Chinese Spouting Bowl Tibetan Bowl PVP Pipes Iron Tube

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