WAVES

Types of Waves Mechanical Electromagnetic Longitudinal Transverse Surface Electromagnetic

WAVES a disturbance that transfers energy Carries energy from one place to another Classified by what they move through (called a medium) Mechanical Waves (need a medium) the energy is transferred by vibrations of medium (medium = matter) Ex. ocean waves move through water, seismic waves, sound waves Electromagnetic waves (do not need medium) the energy moves through disturbances in the electromagnetic field. Ex. light waves, radio, cell towers Physics The act or process of propagating, especially the process by which a disturbance, such as the motion of electromagnetic or sound waves, is transmitted through a medium such as air or water. A medium is a substance or material which carries the wave

Energy of waves By definition, waves transfer energy. The energy spreads out as the wave travels. The bigger the wave the more energy it has. Stand right by some speakers – how does it sound? Look directly into a light – how does it look?

MECHANICAL WAVES require a medium (the material through which the disturbance is moving) to transmit energy travel through & gradually lose energy to that medium Examples: water, sound, rope, & spring waves Mechanical Media: water, air, rope, spring Making a pulse

MECHANICAL WAVES Classified by how medium vibrates                         Classified by how medium vibrates Pulse = direction of energy transfer Vibration = direction of vibration of medium relative to pulse 3 types: Longitudinal, transverse, surface

MECHANICAL WAVES Classified by how medium vibrates Longitudinal Waves: Vibration is in the same direction as wave pulse (parallel to wave pulse) Transverse Waves: Vibration is at 900 (right angles) to wave pulse Surface Waves: Vibration is circular Ex/ Ocean waves; seismic waves

LONGITUDINAL WAVES Vibration is parallel to the direction of the motion of the wave Back and forth (compression & rarefraction) Also called compression or pressure wave Examples: P-type earthquake waves Sound waves Rarefraction (expansion) Compression

TRANVERSE WAVES Sideways or up & down Examples:             Vibration is perpendicular to the direction of the motion of the wave Sideways or up & down Examples: S-type earthquake waves Electromagnetic (EM) or light waves

Waves describe the Earth P waves move through solids & liquids P waves move through solids & liquids S waves move through solids only!!! Are these MECHANICAL WAVES???? YES!! Seismic waves need a medium (the earth!)

WAVE STRUCTURE CREST (peak) AMPLITUDE resting to max peak WAVELENGTH TROUGH

CHARACTERISTICS OF WAVES Crest highest point of a transverse wave Trough lowest point of a transverse wave

AMPLITUDE Distance between “rest & crest” or “rest & trough” Gives indication of “power” or “strength” of wave (magnitude of earthquake = Richter scale) Does not affect velocity of wave Determines loudness (sound) or brightness (electromagnetic wave)

WAVELENGTH  Distance between any two repeating points on a wave crest-crest, trough-trough, expansion-expansion, compression-compression Determines what colors we see; what notes we hear (pitch) Shorter wavelengths have more cycles per minute because they aren’t as long

VELOCITY v the rate at which the energy travels; speed & direction Depends on medium Mechanical waves travel faster through dense mediums EM Waves are faster through less dense mediums

Frequency ƒ How often number of wavelengths that pass any point per second measured in wavelengths/second or cycles/second Hertz (Hz) = number of wavelengths in 1 second Frequency is related to velocity: v = ƒ 

PERIOD T How long Amount of time for one wavelength to pass a point Related inversely to frequency Period = 1 Frequency When an event occurs repeatedly, then we say that the event is periodic and refer to the time for the event to repeat itself as the period.

Internet resources http://www.glenbrook.k12.il.us/gbssci/Phys/Class/waves/wavestoc.html To test how well you understand go to http://www.physicsclassroom.com/Class/waves/u10l1c.cfm#emmech When an event occurs repeatedly, then we say that the event is periodic and refer to the time for the event to repeat itself as the period.