17.1: There are 2 types of waves. Electromagnetic: don’t need a medium to travel. Mechanical: need a medium to travel.

Electromagnetic Spectrum

Medium  The material through which a wave travels.  Solids, liquids, and gases all can act as mediums.

Mechanical wave  is created when a source of energy causes a vibration to travel through a medium.

Types of Mechanical Waves  Transverse waves  Longitudinal waves  Surface waves

Transverse Waves  A wave that causes the medium to vibrate at right angles to the direction in which the wave travels.

Transverse Wave

Longitudinal Waves  Is a wave in which the vibration of the medium is parallel to the direction the wave travels.

Longitudinal Wave  Compression: where the particles in a medium are space close together.  Rarefaction: where the particles in a medium are spread out.

surface wave  A wave that travels along a surface separating two media.

17.2: Properties of Mechanical Waves  Period  Frequency  Wavelength  Speed  Amplitude

Wavelength  The distance between a point on one wave and the same point on the next cycle of the wave

Period  The time required for one cycle, a complete motion that returns to its starting point.

frequency  The number of complete cycles in a given time.  Any periodic motion has a frequency.

Frequency & Hertz  For a wave, the number of wave cycles that pass a point in a given time.  Frequency is measured in cycles per second, or hertz (Hz).

Hertz

Frequency and wavelength for some typical sounds Frequency (Hz) WavelengthTypical Source 2017 metersrumble of thunder cm (27”)average male voice 2,00017 cm (6.7”)fire truck siren 10, cm (1.3”)whine of a jet turbine 20,0001.7cm (2/3”)highest pitched sound you can hear

Wave Speed  Speed = Wavelength x Frequency

amplitude  Of a wave is the maximum displacement of the medium from its rest position.

More amplitude = More energy

17.3: Behavior of Waves  Reflection  Refraction  Diffraction

Interference  Constructive  Destructive

Constructive Interference  When 2 or more waves combine to produce a wave with a larger displacement

Destructive Interference  When 2 or more waves combine to produce a wave with a smaller displacement

Constructive & Destructive Interference

Standing Waves  Is a wave that appears to stay in one place, it does not seem to move through the medium.

Standing waves  Node: a point on a standing wave that has no displacement from the rest position.  Antinode: a point where a crest or trough occurs midway between 2 nodes.

Standing Waves  Forms only if half a wavelength or a multiple of half a wavelength fits exactly into the length of a vibrating cord.

17.4: Sound and Hearing  Speed  Intensity  Loudness  Pitch