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Physical Science Sound and Waves Introduction Slide 2 Mechanical Wave Mechanical waves require a medium Examples: shaking a rope or string, ocean tides, slinky and spring, diffusion of heat, etc. Waves carry energy from one location to another Slide 3 Types of Mechanical Waves Three types Transverse Waves Longitudinal Waves Surface Waves Slide 4 Transverse Waves Particles vibrate perpendicular of the direction the wave travels. Trough is the lowest point and crest is the highest point. Examples: A shaken string; electromagnetic radiation, radio waves, cell phone signals; AC current; etc. Slide 5 Longitudinal Waves Particles vibrate in the direction of propagation! Experiences compression: the area where the particles are most close together and rarefaction: the area where the particles are most distance from one another. Examples: Sound waves, can be made on slinky, air cannons, etc. Slide 6 Surface Waves A surface wave travels along a surface that separates two medium. Slide 7 Wave Properties Period (T) The time required to complete one cycle for a wave. Units are in seconds. Frequency (f) The number of complete cycles in a give time. Units of f are in Hertz (Hz). AKA inverse seconds 1/s This means T=1/f and f=1/T Slide 8 Wave Length! Wavelength () is the distance between crest or toughs for transverse waves and the distance between compressions or rarefactions for longitudinal. Lambda is how your pronounce Wave length units are meters Slide 9 Wave Speed!!!!!! Wave speed is equal to wave length times frequency that is V= x f or if you hate wave speed = frequency x wave length Wave speed has units of meters per second (m/s) The speed of light is always c however! Slide 10 Amplitude This is how big the wave is or rather how large the displacement of the wave is from the origin. Slide 11 Behavior of waves So very many properties. Reflection, Refraction, diffraction, interference, standing waves Slide 12 Reflection Reflection occurs when a wave bounces off a surface/barrier it is on able to pass through. The speed and frequency of the wave does not change during a reflection. Slide 13 Refraction Refraction occurs when the wave enters a new medium at an angle and changes direction. Wave speed does change upon entering a new medium This is how rainbows are created and how ocean waves change direction. Slide 14 Diffraction Diffraction is the bending of a wave through or around an obstacle. This is an important property of light and is often used in quantum mechanics. Slide 15 Interference!!!!!!!!!!!oneone1!!11! This is an extremely important property of waves! There are two types: constructive and destructive Constructive and destructive interference are both examples of the superposition. Superposition is how sound canceling headphones work, amplifiers, musical instruments (via the formation of standing waves There is no music without superposition! Slide 16 Constructive Interference Two like waves combine to have there amplitudes add forming an over all larger amplitude wave. For sound, this makes the sound louder! Slide 17 Destructive Interference Two waves combine to make a smaller amplitude wave. This makes sound more quite and is how sound canceling head phones work! Slide 18 Standing Wave Standing waves only form if multiple half of wavelengths fit into the length of a vibrating cord or string. They have nodes and antinodes Nodes are at a location of zero displacement Antinodes are at the highest points of the wave Slide 19 Sound waves Sound, is again, a longitudinal wave! Sound travels at about 343 m/s at room temperature Slide 20 Decibels The louder a sound is the higher its intensity Larger intensities mean higher decibels A rock concert is often at the threshold of pain and you will lose hearing with out protection Slide 21 Pitch and Frequency A pitch is the frequency of sound as you perceive it. High frequencies yield a high pitch and low frequencies a low pitch Middle C has a frequency of 261 Hz, while an F# has a frequency of about 370 Hz. Well for first harmonics anyways. Slide 22 Doopppplllllleeeeeeerrrrrrrrrrrrrr The Doppler effect is the change in frequency of a sound caused by the motion of the listener and/or source. This effect also affects light from distance stars and is known as red/blue shifted light. http://www.youtube.com/watch?v=Y5KaeCZ_AaY Slide 23 Electromagnetic Waves! AKA light and much more! Electromagnetic waves are created from accelerating electrons. Electromagnetic waves can travel through a vacuum and matter. This means an electromagnetic wave require no medium to travel! Slide 24 Electromagnetic Wave Speed All electromagnetic waves travel at c, the speed of light in a vacuum. Also, Electromagnetic is often abbreviated as EM. Slide 25 EM frequency Electromagnetic waves can vary in wavelength and frequency Again v = f x However, v = c for EM waves unless otherwise stated. Slide 26 EM Waves Behavior EM waves behave very peculiar, they behave both like waves and particles. This is known as wave particle duality and was discovered by Albert Einstein during his studying of the photoelectric effect. EM energy is carried by little particles called photons and a photons energy is dependent on a waves frequency. Slide 27 Wave Spectrum!!! EM waves come in all sorts of variety and are not just limited to visible light. Slide 28 Radio Waves Includes both FM (frequency modulated) and AM (amplitude modulated) wavelength Also includes: TVs Slide 29 Microwaves Includes microwaves (hopefully obviously) Microwaves work by hitting the dipole moments in fats and water stored in food producing thermal energy Also includes: radar Slide 30 Infrared Waves Infrared is the wave length of light are bodies give off and most objects produce. Infrared light is also used in TV remotes Some infrared light can be seen by your cell phones camera! Slide 31 Visible Light This is the ROY G. BIV we see from a rainbow and is the light we can see. Slide 32 Ultraviolet Waves This is the invisible light produced by the sun responsible for sun burns! It can kill a large amount of germs and bacteria and is often used for medical sterilization Slide 33 X-Rays X rays have very short wave lengths and have a high energy They can penetrate a large amount of matter and are often used in medical applications Slide 34 Gamma Rays The highest frequency waves possible. These waves can slice through cell membranes and damage your DNA possibly causing cancer It is also used to treat cancer however, by destroying the cancer cells! Slide 35 Video of light colors! If theres time http://www.youtube.com/watch?v=S9dqJRyk0YM