Waves Chapters 11, 12, 13

CH 11-1 The Nature of Waves  wave: repeating disturbance or movement that transfers energy through matter or space  Figure 2 page 327  All waves are produced by vibrations.

Mechanical Waves  medium: the matter the waves travel through  The medium can be solid, liquid, gas, or a combination of these.  What is the medium for sound waves? air air  What is the medium for ocean waves? water water

 As a wave travels through a medium, particles of the medium do not travel with the wave.  So, what do waves carry?

Two Types of Mechanical Waves 1. transverse waves: matter in the medium moves back and forth at right angles to the direction the wave travels 2. compressional (longitudinal) waves: matter in the medium moves back and forth in the same direction that the wave travels

Transverse Waves

Compressional Waves

 The arrows represent motion of particles of a medium and the motion of a wave traveling through the medium. Which combination best represents transverse waves? A. B. C. D.

Three Types of Waves  Sound waves compressional wave compressional wave When a sound wave reaches your ear, it causes your eardrum to vibrate. Your inner ear then sends signals to your brain and your brain interprets the signals as sound. When a sound wave reaches your ear, it causes your eardrum to vibrate. Your inner ear then sends signals to your brain and your brain interprets the signals as sound.

Three Types of Waves  Water waves transverse (but not purely) transverse (but not purely) Ocean waves are caused by wind blowing across the water. The changing wind speed acts like a vibration. Ocean waves are caused by wind blowing across the water. The changing wind speed acts like a vibration.

Three Types of Waves  Seismic waves combination of compressional and transverse combination of compressional and transverse

CH 11-2—Wave Properties  Parts of a transverse wave crest: highest point on a transverse wave crest: highest point on a transverse wave trough: lowest point on a transverse wave trough: lowest point on a transverse wave

 Parts of a compressional wave compression: crowded regions of a longitudinal wave compression: crowded regions of a longitudinal wave rarefaction: spread out regions of a longitudinal wave rarefaction: spread out regions of a longitudinal wave

Properties of a Wave  wavelength: distance between one point on a wave and the nearest point just like it crest to crest, trough to trough (transverse) crest to crest, trough to trough (transverse) compression to compression, rarefaction to rarefaction (longitudinal) compression to compression, rarefaction to rarefaction (longitudinal)

 frequency: number of wavelengths that pass a fixed point each second  Finding frequency: transverse wave—count # of crests or troughs that pass by a point each second transverse wave—count # of crests or troughs that pass by a point each second compressional wave—count # of compressions or rarefactions that pass by a point each second compressional wave—count # of compressions or rarefactions that pass by a point each second  SI unit for frequency: Hertz (Hz)

 Frequency and wavelength are related. As frequency increases, wavelength decreases.

Calculating Wave Speed  velocity = wavelength x frequency v = λ x f  A wave is traveling at a speed of 18 m/s with a frequency of 3 Hz. A second wave is traveling at a speed of 16 m/s with a frequency of 4 Hz. What is the difference in the two wavelengths? 2 m 2 m

 amplitude: maximum distance the particles of a medium are disturbed from their resting positions transverse: distance from the crest or trough of the wave to the rest position of the medium transverse: distance from the crest or trough of the wave to the rest position of the medium compressional: related to how tightly the medium is pushed together at the compressions compressional: related to how tightly the medium is pushed together at the compressions  The greater amplitude—the more energy carried by the wave.

CH 11-3 The Behavior of Waves Reflection  Reflection occurs when a wave strikes an object and bounces off of it.  All types of waves, including sound, water, and light waves, can be reflected.

Refraction  A wave’s speed depends on the medium it is moving through.  Refraction is the bending of a wave caused by a change in its speed as it moves from one medium to another.  The greater the change in speed, the more the wave bends.

Diffraction  Diffraction occurs when an object causes a wave to change direction and bend around it.  Waves can also be diffracted when they pass through a narrow opening.

Interference  Interference occurs when two or more waves overlap and combine to form a new wave.  This new wave exists only while the original waves continue to overlap.

Resonance  The ability of an object to vibrate by absorbing energy at its natural frequency is called resonance.