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What are waves? These are just one of many examples of waves... 1 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.” 2 Scientists use pendulums to determine predictable cycles in things such as: Because these cycles are predictable, we can use them to “mark” time. 3 (Harmonic Motion) Rhythmic disturbances that carry energy through matter and space Results when matter vibrates. 4 Waves can travel through space. Waves are made when you speak. And make the light you see as light. 5 How dolphins communicate Waves can travel through a medium. Music from your radio to your ear Solid – earth quake is the material in which a wave moves. 6 But there are some waves that don’t travel through a medium… Microwaves Radio Larger Waves Infrared Visible X-Ray Ultraviolet Gamma Smaller Waves Electromagnetic waves such as visible light travel throughout “matter-less” space. More on this later... 7 Waves can be easily understood through... ...a wave whose oscillations are perpendicular to the direction the wave travels. 8 Crest – top of the wave Trough Crest Trough – bottom of the wave 9 Wavelength Nodal Line Amplitude Wavelength – distance to include 1 crest and 1 trough- represented by ( – גLambda) symbol or Amplitude – (volume) height of crest or trough from nodal line measured in decibels (db) and is the total energy of the wave. Nodal Line-resting line 10 11 Wave frequency is the amount of waves that move through a point per second and is measured in the units of Hertz (Hz). Point A The diagram above shows 3 waves going through point A in 1 second. The frequency would be 3 Hz. 12 Calculating the Velocity of a Wave To find the velocity or speed of a wave, use the following equation: Velocity = Wavelength X Frequency V=גxf V = Velocity in m/s ( = )גWavelength in meters (m) f = Frequency in hertz (Hz) 13 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? Remember the 4 step process to solving equations … = 5 m F = 2 Hz V = 10m/s Formula Substitute Answer V= x f 5m x 2Hz 10 m/s 14 Do problems 1, 2 & 3 in your notes. Hint: You may have to manipulate the formula – make a triangle. 15 Longitudinal Waves Also called compressional waves. 16 Longitudinal Waves Compression - part where molecules are pushed together Rarefaction - part where molecules are spread apart nodal line Compression Wavelength amplitude Rarefaction Wavelength – 1 Compression and 1 Rarefaction 17 18 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 19 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! 20 21 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. 22 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 23 Interference • When 2 or more waves pass through a medium at the same time. Constructive Hit the nodal line together. Basically music. IN PHASE Destructive Hit the nodal line at different times. Basically noise. OUT OF PHASE 24 25 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 forceamplitude grows, Example-swing set 26 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 27 28 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 waves • S waves • Surface waves 29 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 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. 33