1 What are waves? These are just one of many examples of waves...

2 Waves Are a Form of Harmonic Motion Motion that repeats over and over… The pendulum is an example. “There and Back Again” -- this represents 1 cycle or “period.”

3 Scientists use pendulums to determine predictable cycles in things such as: Because these cycles are predictable, we can use them to “mark” time.

4 Rhythmic disturbances that carry energy through matter and space (Harmonic Motion) Results when matter vibrates.

5 Waves are made when you speak. Waves can travel through space. Waves can make the earth move and shake. And make the light you see as light.

6 Waves can travel through a medium. is the material in which a wave moves. How dolphins communicate Solid – earth quake Music from your radio to your ear

7 But there are some waves that don’t travel through a medium… Electromagnetic waves such as visible light travel throughout “matter-less” space. More on this later... Radio Microwaves InfraredUltraviolet Visible X-Ray Gamma Larger Waves Smaller Waves

8 Waves can be easily understood through......a wave whose oscillations are perpendicular to the direction the wave travels.

9 Crest – top of the wave Trough – bottom of the wave Crest Trough

10 Amplitude Wavelength or Wavelength – distance to include 1 crest and 1 trough- represented by (ג – Lambda) symbol Amplitude – (volume) height of crest or trough from nodal line measured in decibels (db) and is the total energy of the wave. Nodal Line Nodal Line-resting line

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12 Wave frequency is the amount of waves that move through a point per second and is measured in the units of Hertz (Hz). The frequency would be 3 Hz. Point A The diagram above shows 3 waves going through point A in 1 second.

13 Calculating the Velocity of a Wave To find the velocity or speed of a wave, use the following equation: Velocity = Wavelength X Frequency V = ג x f V = Velocity in m/s (ג) = Wavelength in meters (m) f = Frequency in hertz (Hz)

14 Calculating the Velocity of a Wave A wave moves through water. The length of the wave is 5 meters. The frequency is 2 waves per second (2 Hz). What is the velocity of the wave? = F = V = 2 Hz 5 m 10m/s V= x f 5m x 2Hz 10 m/s Remember the 4 step process to solving equations …

15 Do problems 1, 2 & 3 in your notes. Hint: You may have to manipulate the formula – make a triangle.

16 Longitudinal Waves Also called compressional waves.

17 Longitudinal Waves Compression Rarefaction Wavelength Rarefaction - part where molecules are spread apart Compression - part where molecules are pushed together Wavelength – 1 Compression and 1 Rarefaction nodal line amplitude

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19 Reflection the bouncing back of a wave as it strikes a hard surface. Reverberation – Combination of reflected waves Multiple Echoes like in concerts Example: when a water wave from the ocean hits the beach

20 Diffraction when waves spread out past the edge of a barrier or through holes in the barrier. Example: You can hear someone talking around a corner, because the waves move beyond the wall. This is going to be a great surprise! Not anymore!

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22 Refraction To change the direction of a wave as it passes from one medium to another. The frequency doesn’t change, but the speed and wavelength do – they slow down.

23 Absorption A wave that can be absorbed by the medium material and disappear. The amplitude of the wave gets smaller and smaller. Examples: sponge absorbs water wave heavy curtain absorbs sound waves and dark glass absorbs light waves

24 Interference When 2 or more waves pass through a medium at the same time. Constructive Destructive Hit the nodal line together. Basically music. IN PHASE Hit the nodal line at different times. Basically noise. OUT OF PHASE

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26 Natural Frequency and Resonance Natural Frequency –A special frequency at which objects vibrate if they are disturbed –All things in the universe have a natural frequency –Changing the natural frequency: of a string-by tightness, lengthening or weight of string in a system-change the factors that affect the size, inertia or forces in the system. Resonance –Having the natural frequency of the system exactly in tune with your force- amplitude grows, Example-swing set

27 Standing waves on a string Standing wave –A wave that is trapped in one spot Fundamental –Natural frequency of a wave Harmonic –Fundamental and multiples of its frequency –Node-point where the string does not move –Antinode-points of the greatest amplitude –Wavelength is the length of one complete “S” shape of the string

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Seismic Waves 29 Seismic waves are vibrations that travel through Earth, carrying energy released during an earthquake. Earthquakes produce three main types of seismic waves: P waves S waves Surface waves

P waves P waves are longitudinal waves similar to sound waves. P waves compress and expand the ground like an accordion. They are the fastest seismic waves. They can travel through both solids and liquids. 30

S waves S waves are transverse waves, like light and other electromagnetic radiation. S waves cause particles in the material they pass through to vibrate at right angles to the direction in which the waves move. Unlike P waves, S waves cannot travel through liquids. 31

Surface Waves Surface waves are waves that develop when seismic waves reach Earth’s surface. Surface waves move more slowly than P waves or S waves. Surface waves usually produce larger ground movements and more damage than other types of seismic waves. Some surface waves are transverse waves, and others have a rolling motion similar to ocean waves. 32

33 Earth’s liquid outer core blocks S waves and refracts P waves. The result is a shadow zone where no direct seismic waves from an earthquake are detected.