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Is it Matter? Slide 2 7.1 Waves Mr. Perez Slide 3 What are waves? Waves are disturbances that move through matter or space Waves TRANSFER ENERGY, NOT MATTER from place to place Waves are made by vibrating objects The energy in the vibrations transfer the waves outward Slide 4 Types of Waves Mechanical waves- waves that can only travel through matter and not through space Transverse waves Longitudinal (Compressional) waves Electromagnetic waves- waves that can travel through both matter and space Slide 5 Transverse waves Type of mechanical wave Causes particles in matter to move at right angles to the direction in which the wave travels Slide 6 Longitudinal (Compressional) waves Type of mechanical wave Causes particles in matter to move back and forth along the same direction in which the wave is traveling Slide 7 Seismic waves Type of mechanical wave Waves move through the ground during an earthquake Some are compressional (longitudinal) and others are transverse Rolling waves: cause the ground to move up and down and back and forth Slide 8 Electromagnetic waves Type of transverse wave Contain electric and magnetic parts that vibrate up and down perpendicular to the direction the wave travels Light, radio waves and X rays are some examples Slide 9 Properties of Waves All waves have properties that depend on the vibrations that produce them 1.Wavelength 2.Frequency 3.Amplitude 4.Speed Slide 10 Wavelength () The distance between any point on a wave and the nearest point just like it Transverse: crest to crest or trough to trough Longitudinal (compressional): compression to compression or rarefaction to rarefaction Measured in meters (m) Slide 11 Frequency Number of wavelengths that pass by a point each second Measured in Hertz (Hz) 1 Hz = 1 wavelength per second 1 Hz = 1/s Slide 12 Amplitude Maximum distance that matter moves as the wave passes Transverse: top of crest or bottom of trough to resting position Longitudinal (compressional): more squeezed together compressions and more spread apart rarefactions Slide 13 Amplitude and Energy The larger the amplitude of a wave, the more energy the wave carries Slide 14 Speed How fast a wave travels Measured in meters per second (m/s) Wavelength formula: Slide 15 Closing Questions Create a venn diagram comparing and contrasting mechanical waves and electromagnetic waves. If a wave is traveling at a speed of 45 m/s, and has a frequency of 9 Hz, what is the waves wavelength ( )? How do waves transfer energy, but not matter? Slide 16 Waves can change direction When you see your own reflection, light is changing direction back at you Waves can also travel from one material to another REFLECT- bounce off a surface REFRACT- bend DIFFRACT- bend around an obstacle Slide 17 Law of reflection The angle that the incoming wave (i) makes with the normal equals the angle that the outgoing wave (r) makes with the normal Slide 18 Refraction Speed of a wave depends on the properties of the material through which it travels Change in speed causes waves to bend Refraction is the change in direction of a wave when it changes speed as it travels from one material to another Slide 19 Diffraction Bending of waves around an object Depends on the size of the obstacle The bigger the wavelength compared to the size of the obstacle, the amount of diffraction increases Slide 20 Particles and Waves Both particles and waves transport energy from one place to another However, Particles have mass and volume and can carry an electric charge Waves have wavelength, frequency, amplitude Slide 21 Links http://www.bbc.co.uk/schools/gcsebitesize/science/ed excel/visiblelight_solarsystem/wavesact.shtml http://www.bbc.co.uk/schools/gcsebitesize/science/ed excel/visiblelight_solarsystem/wavesact.shtml http://www.classzone.com/books/ml_science_share/vis _sim/wslm05_pg18_graph/wslm05_pg18_graph.html http://www.classzone.com/books/ml_science_share/vis _sim/wslm05_pg18_graph/wslm05_pg18_graph.html http://phet.colorado.edu/sims/wave-on-a-string/wave- on-a-string_en.html http://phet.colorado.edu/sims/wave-on-a-string/wave- on-a-string_en.html Slide 22 References Florida Science Grade 7, Glencoe Science & McGraw Hill Publishing Google image search