Vibrations and Waves 12-3 Properties of Waves

Wave Motion A wave is the motion of a disturbance. Waves of almost every kind require a material medium to travel through. Waves that require a material medium are called mechanical waves. Medium – material through which a disturbance travels. Ex: water, air Mechanical waves : waves that require a material medium Ex: Sound waves – without air as a medium to travel through, there would be no sound. Figure 12-10 A pebble dropped into a pond creates ripple waves similar to those shown here.

Wave Types A wave that consists of a single traveling pulse is called a pulse wave. When you have several pulses generated, these pulses form a periodic wave. Figure 12-11 A single flip of a wrist on a taut rope creates a pulse wave.

Wave Types When a waves displacement is perpendicular to its motion, this is called a transverse wave. When particles vibrate parallel to direction of wave motion, this is called a longitudinal wave.

Longitudinal waves These are also known as Compression Waves. Compressions – More dense; darker area (crest) RareFactions – Less dense area (trough)

Parts of a Wave Crest - Highest point above equilibrium. Trough – Lowest point below equilibrium. Wavelength – Distance the wave travels during one cycle ().

Wave Speed Wave speed equals frequency times wavelength. Formula = Speed of Wave = frequency x wavelength v = f

Waves Transfer Energy The rate at which waves transfer energy depends on amplitude. The greater the amplitude, the more energy a wave carries in a given time interval.

Guided Practice Open Books to page 457 Sample 12D

Vibrations and Waves 12-4 Wave Interactions

Wave Interference Two different material objects can never occupy the same space at the same time. Waves, however, can pass through one another. When this happens, the waves form an interference pattern. Figure 12-17 This ripple tank demonstrates the interference of water waves.

Types of Interference Constructive interference – displacements on same side of equilibrium. The method of summing the displacements of waves is known as the superposition principle. Figure 12-18 When these two wave pulses meet, the displacements at each point add up to form a resultant wave. This is an example of constructive interference.

Types of Interference Destructive Interference – displacements on opposite sides of equilibrium. Complete Destructive Interference – two pulses equal in amplitude but on opposite sides of equilibrium completely cancel each other. Figure 12-19 In this case, known as destructive interference, the displacement of one pulse is subtracted from the displacement of the other.

Reflection At a free boundary, waves are reflected. At a fixed boundary, waves are reflected and inverted.

Standing Waves Standing waves have nodes and antinodes. The points at which two waves cancel are nodes Between two adjacent nodes where the amplitude is the greatest, these points are called anti nodes.