1. 12-3 Properties of Waves

2.  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.

3.  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.

4. 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.

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

6.  Crest - Highest point above equilibrium.  Trough – Lowest point below equilibrium.  Wavelength – Distance the wave travels during one cycle ( ).

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

8.  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.

9.  Open Books to page 457  Sample 12D

10. 12-4 Wave Interactions

11.  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.

12.  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.

13.  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.

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

15.  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.