Waves Chapter 15

Waves Wave a disturbance that carries energy through matter or space If there is a leaf floating on water and a wave comes through the area the leaf will not move with the wave After the wave passes the leaf will return to its original location The only thing to pass with the wave is energy

Waves Most waves travel through a medium Medium matter through which a wave travels Air Water Mechanical waves require a medium Most waves are mechanical waves

Waves Electromagnetic waves waves that do not require a medium light does not need a medium The light that the sun radiates can travel to earth through empty space meaning no medium Radio waves are another example of electromagnetic waves

Waves Energy is the ability to do work We know waves have energy because they can do work Sound waves do work on our ear drum Water waves do work on boats The larger the wave the more energy it has Tsunamis’ are huge waves that have enough energy to destroy coastal land and homes (which is essentially doing work to this area)

Waves The energy waves have spread out as it travels through a medium If you stand right next to a loud speaker this could damage your ear drum If you stand 100 meters from the speaker it will not damage your ear drum The reason for this is because waves spread out and lose energy as they spread out in space

Waves & Vibrations Most waves are caused by vibrations Sound waves are produced by the vibration of vocal cords Electromagnetic waves are cause by charged particles vibrating

How we hear Sound waves travel through the area Sound waves are gathered by the tympanic membrane of the ear The tympanic membrane vibrates the bones in the ear to amplify the sound The vibrations made by the bones trigger electrical pulses to our brain which decipher sounds

Harmonic Motion If you have a spring and pull it down and release it the spring will bounce up and down until it releases all of its energy simple harmonic motion If you have masses connect by springs and you cause one mass to vibrate the vibrations will move to each mass through the springs that connect them this is called damped harmonic motion

Transverse waves Transverse wave is a wave in which the wave motion is perpendicular to the particle motion Examples electromagnetic waves

Longitudinal waves Longitudinal wave is a wave in which the wave motion is parallel to the particle motion Examples sound waves

Parts of a transverse wave

Parts of a longitudinal wave

Surface waves Surface waves are water waves The particles move both perpendicularly and parallel to the direction in which the wave travels Surface waves move in an ellipse

Surface wave

Wave properties Amplitude from the rest point to the trough or the rest point to the crest The larger the amplitude the more energy a wave has

Wave properties Wavelength distance between two identical points on a wave The shorter the wavelength the more energy it carries

Wave properties An ideal transverse wave has the shape of a sine curve Sound waves’ wavelengths are difficult to find because of their odd shapes When calculating wave length in an equation it is represented by the greek letter lambda Wave length is measured in meters

Period Period is a measurement of the time it takes for a wave to pass a given point In a equation period is represented by the letter “T” SI unit is seconds

Frequency Frequency the number of wavelengths that pass a point in a given time The symbol for frequency is “f” The SI unit is hertz 1 hertz is equal to 1 vibration in 1 second

Wave speed SI units is m/s

Wave speed

Speed of waves Sound waves travel so quickly through air that we do not notice the time delay between the sound made and us hearing the sound Sound travels faster through water (3 to 4 times faster) Sound travels 15 to 20 times faster on a solid surface such as a metal The speed of a wave depends on the medium it is passing through

Speed of sound waves Kinetic theory determines how fast waves move Sound moving through air is moving through a gas which means that the particles are far apart and it takes longer for the particles to collide together and connect the wave to the next particle Liquids have particles closer together and take less time However, solid particles are so closely packed together it takes very little time for the particles to communicate the wave between each other

Light Light does take time to travel from place to place The speed that light travels is known as the speed of light The speed of light in empty space is equal to 3.00 x 108 This constant is represented by the symbol “c” Light passes slower through a medium than empty space

Light We are able to see light with frequencies of 4.3 x 1014 Hz to 7.5 x 1014 Hz The light we can see is known as visible light Each color has its own frequency which gives it the color we are able to see Frequency x wavelength = speed of light

Doppler Effect The closer you are to a sound the louder the sound is The pitch changes depending on the frequency of the sound Higher pitches have a high frequency Distance from you and the sound source can change the frequency which changes the pitch that we hear The closer we are to the sound the higher pitch that it has

Reflection Reflection the bouncing back of a wave when it meets a surface or boundary

Diffraction Diffraction a change in direction of a wave when the wave finds an obstacle or an edge If you walk past a door and can hear voices inside talking their voices are diffracting through the door and edges in the room to your ear to be heard Depending on what objects the wave diffracts from determines how well you can hear the sound waves

Refraction Refraction the bending of a wave as they pass from one medium to another The part of the straw under the water has a different medium so it changes the angle of refraction

Interference Waves can share space with other waves, unlike human bodies Interference when several waves are in the same location, they combine to produce a single, new wave that is different from the original wave Once the wave passes the other particles will return to their original state

Con vs. De Constructive Interference Destructive Interference When two or more waves combine together and increases their amplitude A wave of 3 cm meets a wave of 4 cm The new wave has an amplitude of 7 cm When two or more waves hit each other and they work against each other to decrease their amplitude A 3 cm wave meets a 4 cm wave Forms a 1 cm wave

Interference

Interference If you use two tuning forks with different frequencies you create a beat Each wave reaches your ear at a different time which change the sound of the beat The alternating loud and soft sounds from different frequencies help create beats

Standing waves Standing waves results from interference between a wave and its reflected wave