Waves http://www.youtube.com/watch?v=OGyRe_SGnck Bill Nye Tsunami http://www.youtube.com/watch?v=Q5x6a5kAke0

What is a wave? Wave: A repeating disturbance or movement that transfers energy Examples: ocean waves, sound, light

How do waves travel? Waves travel though matter, this matter is called a medium Solid: earth Liquid: water Gas: air Light waves do not need a medium to travel through

Mechanical Waves Mechanical Waves: can only travel through matter Transverse waves: the medium moves at a right angles to the direction of the wave Example: in the ocean Compressional waves: the medium moves along the same direction of the wave Example: a coiled spring (slinky), sound waves

Waves and Energy Waves and energy: waves transport energy without transporting matter

Sound waves Sound waves: compressional waves caused by air molecules vibrating Can travel through solids, liquids and gases

Water waves Caused by wind Anything on the surface of the water absorbs some of the energy of the wave The size of the waves depends on Speed of the wind How long the wind blows Distance the wind blows over the water http://www.youtube.com/watch?v=5WleqFcMP8s http://www.youtube.com/watch?v=Ti7nZwxUEjU

Seismic Waves Seismic waves: waves that travel through the earth’s crust They transfer some of the energy to the earth and things on the surface of earth (buildings etc.) http://www.classzone.com/books/earth_science/terc/content/visualizations/es 1002/es1002page01.cfm

Wave properties Crest: the highest point of the wave Trough: the lowest point of the wave Wavelength: the distance from trough to trough or crest to crest Frequency: the number of wavelengths that pass a fixed point in one second (measured in hertz) 1 Hz = 1 wavelength per second Period: the time it takes for one wavelength to pas a fixed point (measured in seconds) Amplitude: the height of the wave

Sound Waves Rarefaction: area of the wave that is not as compressed

Wave Properties Amplitude and energy: the higher the amplitude, the more energy the wave is transferring Frequency and wavelength: the higher the frequency, the shorter the wavelength Frequency and energy: the higher the frequency the more energy the wave has Calculating wave speed: v = ƒλ λ = v/ƒ ƒ= v/ λ

Learning check What is the material called that waves pass through? What type of wave is above? What causes waves in the ocean? Which part is the trough? Crest? Amplitude? Wavelength? c d

Learning Check 8. Frequency is measured in _____________. 9. What is the equation to find out the speed of a wave? 10. Which wave has the longest wavelength? 11. Which wave has the highest frequency? 12. Which wave has the most energy?

Behavior of waves Reflection: when a wave strikes an object and bounces off of it Light: reflection in a mirror Sound: echoes in a canyon

The Law of Reflection The Law of Reflection: the angle of incidence is equal to the angle of reflection

Refraction Refraction: the bending of a wave caused by a change in its speed as it moves from one medium to another The wave bends more when there is a greater change in speed between the 2 substances

Diffraction Diffraction: when an object causes a wave to change direction and bend around it

Diffraction of sound Sound waves diffract around openings in solid surfaces easily

Diffraction and light Light waves are tiny so diffraction doesn’t affect them very much

Diffraction Light bending to create invisibility http://www.youtube.com/watch?v=ScaxoyDIrqs

Radiowaves AM frequency waves have longer wavelengths than FM radiowaves AM radiowaves can diffract around buildings and mountains much easier so the reception is clearer FM radiowaves sound much clearer but have a shorter range

Interference Interference: when 2 waves combine to make a new wave http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/light.htm

Interference Constructive interference: two waves over lap and their amplitudes are added together Crest lines up with crest Said to be “in phase”

If this was a sound wave, what would happen to the sound? If this was a water wave, what would happen to the water? If this was a light wave, what would happen to the light?

Interference Destructive interference: two waves overlap and their amplitudes are subtracted Crest of 1st wave meets trough of the 2nd wave Said to be “out of phase”

If this was a sound wave, what would happen to the sound? If this was a water wave, what would happen to the water? If this was a light wave, what would happen to the light?

Standing Waves http://www.youtue.com/watch?v=NpEevfOU4Z8 Standing wave: when waves that have the same wavelength and amplitude traveling in opposite directions interfere with each other Nodes: places where 2 standing waveswaves cancel each other Antinodes: where vibrating occurs between nodes

Standing waves in music Violin or guitar string: vibrates creating a standing wave Flute: vibrates a column of air creating a standing wave Drums: vibrates a tightly stretched material creating a standing wave http://www.youtube.com/watch?v=lImQH0RD0NU &feature=related

Resonance http://www. youtube. com/watch. v=1yaqUI4b974 http://www Resonance: an object vibrates by absorbing energy at its natural frequencies If enough energy is put in, the object could break apart Bridge affected by constructive interference of its natural resonance frequency http://www.youtube.com/watch?v=3mclp9QmCGs Resonance and tuning forks http://www.youtube.com/watch?v=hiHOqMOJTH4

Learning Check What is it called when waves overlap and either increases or decrease their effect? What is it called when a wave bounces off an object and returns? What is it called when a wave bends when it travels around an object? What is it called when light bends when it enters a different medium? All objects vibrate at a natural frequency called ________________.

Learning Check 6. Which type of radiowave will give you better reception if you are traveling through the mountains? 7. If 2 waves combine to make a bigger wave it is called ______________________. 8. If 2 waves combine to make a smaller wave, it is called _____________________.