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

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• *What are waves?These are just one of many examples of waves...

• *Waves Are a Form of Harmonic MotionMotion that repeats over and overThe pendulum is an example.There and Back Again -- this represents 1 cycle or period.

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

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

• *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.

• *Waves can travel through a medium.is the material in which a wave moves.How dolphins communicate

• *But there are some waves that dont travel through a mediumMore on this later...

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

• *Crest top of the waveTrough bottom of the wave

• *AmplitudeWavelengthorWavelength distance to include 1 crest and 1 trough- represented by ( Lambda) symbolAmplitude (volume) height of crest or trough from nodal line measured in decibels (db) and is the total energy of the wave. Nodal LineNodal Line-resting line

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

• *Calculating the Velocity of a WaveTo find the velocity or speed of a wave, use the following equation:Velocity = Wavelength X FrequencyV = x fV = Velocity in m/s() = Wavelength in meters (m)

f = Frequency in hertz (Hz)

• *Calculating the Velocity of a WaveA 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 Hz5 m10m/sV= x f5m x 2Hz10 m/sRemember the 4 step process to solving equations

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

• *Longitudinal WavesAlso called compressional waves.

• *Longitudinal WavesRarefaction - part where molecules are spread apartCompression - part where molecules are pushed together

Wavelength 1 Compression and 1 Rarefactionnodal lineamplitude

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• *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

• *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.

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• *Refraction

To change the direction of a wave as it passes from one medium to another. The frequency doesnt change, but the speed and wavelength do they slow down.

• *AbsorptionA 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

• *Interference

When 2 or more waves pass through a medium at the same time.ConstructiveDestructiveHit the nodal line together.Basically music.IN PHASEHit the nodal line at different times.Basically noise.OUT OF PHASE

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• *Natural Frequency and ResonanceNatural FrequencyA special frequency at which objects vibrate if they are disturbedAll things in the universe have a natural frequencyChanging the natural frequency:of a string-by tightness, lengthening or weight of stringin a system-change the factors that affect the size, inertia or forces in the system.ResonanceHaving the natural frequency of the system exactly in tune with your force-amplitude grows, Example-swing set

• *Standing waves on a stringStanding waveA wave that is trapped in one spotFundamentalNatural frequency of a waveHarmonicFundamental and multiples of its frequencyNode-point where the string does not moveAntinode-points of the greatest amplitudeWavelength is the length of one complete S shape of the string

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• Seismic Waves*Seismic waves are vibrations that travel through Earth, carrying energy released during an earthquake. Earthquakes produce three main types of seismic waves:P wavesS wavesSurface waves

• P wavesP 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.

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• 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.

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• Surface WavesSurface waves are waves that develop when seismic waves reach Earths 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.*

• *Earths 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.

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