Heres the basics: 1. Waves are caused by vibrations or disturbances. 2. A single wave is called a Pulse Wave (or wave pulse). 3. When waves are caused by vibrations/disturbances in a medium, and the wave NEEDS the medium to propagate (move) then it is called a Mechanical Wave. 4. Some waves are caused by vibrations but DO NOT need a medium to travel. These are called Electromagnetic Waves. Do I need to know this ?? R. Fonash Heres what you really need to know: Mechanical waves can be Transverse Waves (Light), Longitudinal Waves (Sound), or Combination Waves (Ocean waves) Electromagnetic Waves only can be Transverse Waves. All Waves have wavelength, amplitude, frequency, and velocity. R. Fonash Transverse waves are travelling waves that push the medium around it perpendicularly (or transversely) to the direction of travel of the wave. Key terms: Amplitude the height of a wave from the middle line to the crest or the trough. Crest the top of the wave. Trough the bottom of the wave. Wavelength the distance from a point on a wave to a repeating point. Lamda () the symbol for wavelength/ They look like a snake when they travel ! Key terms: Compression the part of the wave where the medium is compressed. Rarefaction the part of the wave where the medium is spread apart. Longitudinal waves are travelling waves that push the medium around it parallel to the direction of travel of the wave. It looks like a multi-car pile-up ! The wavelength is the distance between consecutive repeating points on the wave. Longitudinal Wave R. Fonash The amplitude of a longitudinal wave is the thickness of the compression. Large Amplitude R. Fonash The frequency is the rate at which waves pass a certain point. The frequency is the number of waves which travel past in one second. Its symbol is (f) and the unit for frequency is the Hertz (hz) Frequency is also called: cycles per second The time to complete one full wave cycle is called the Period. Its symbol is (T) and its unit is seconds (s). Remember: T=1/f and f=1/T so, if you know one, you can compute the other. R. Fonash When waves travel, they can move at different speeds. The speed that a wave travels is given by the mathematical equation: This means that the speed (velocity) of a wave is the product of the frequency and the wavelength. Practice problem: A wave begins in a stadium. The spectators wave their arms every time the wave comes around every 10 seconds. The perimeter of the stadium is 20 meters. How fast does the wave travel around the stadium? Lets work together to solve this.... v = f R. Fonash All waves both Transverse and Longitudinal, will REFLECT when the reach a hard surface. Sound waves are called Echoes Light waves are called Reflections Remember that since light waves (transverse) flip or invert, we see them in the mirror as being backward. Since sound waves (longitudinal) do not flip to either side but bounce straight back, we hear them just as we produced them echoes. R. Fonash When waves pass from one medium to another (like going from the air into water, or from water through oil), they will not only reflect; they can also continue going into the new medium. This is called Absorption. Sometimes when they make this change from one medium to another they stop. Sometimes they continue going but will usually change speed and/or direction when they do it. R. Fonash When waves reflect, we already know that they usually invert (flip). We also already know that when 2 waves pass through each other, they interfere with each others amplitude. Now, when incoming waves and reflected waves are in phase , or on the same side of the equilibrium line, they cause Constructive Interference. (This means that they form a single wave which has a greater amplitude than either of the two individual waves.) R. Fonash But, if the reflected wave is out-of-phase with the incoming wave, then the crests of one wave and the troughs of the other wave will match up. This is called Destructive Interference. R. Fonash In special circumstances, reflected waves will interact with each other JUST RIGHT. When they do, you will get combinations of constructive AND destructive interference and a STANDING WAVE appears. Different forms of standing waves are called harmonics in both Physics class and Music class. The most basic harmonic is called the fundamental harmonic. It is like a jump rope. (The points of a standing wave that DO NOT move are called the nodes. The parts of the wave that move are called anti-nodes.) R. Fonash When a wave goes from one medium to another, it will bend. This is called Refraction. Think of when you look into a pond or through a glass of water. An object in either of these will appear to be in a different spot from where it actually is. This is because light waves bend (refract) when they go from air to water or from water to air. R. Fonash Or think about when you are in a pool of water. The sounds and voices you hear are very different from when you are out of the water. This is because the sound waves bend and change speed when the medium changes. R. Fonash Or maybe think about when you look into a pond or lake for a fish. The fish are not exactly where you thought they would be. Remember that since light is a wave and it is passing from the air into the water, it will refract (bend) and the fish will not be where it appears to be. R. Fonash Refraction is also the reason why rainbows exist. When light passes through a raindrop, it refracts ( bends ). Under the right conditions, the light will also break into different colors. The raindrop is called a PRISM. Anybody remember the colors of the rainbow? R. Fonash This is how a prism works: When light is passed through a specially cut piece of glass (or a raindrop), the light will bend. Blue light bends more than red light. Green light is in the middle and bends somewhere in between. The amount the light bends depends on the frequency of the wave. R. Fonash White light is all colors of the rainbow added together. R + O + Y + G + B + I + V = WHITE LIGHT Red light has long wavelengths and low frequency. Green light is in the middle. Blue light has short wavelengths and high frequency. Color byPIGMENT (paint, ink, crayons) Primary Colors are: RedMagenta BlueCyan YellowYellow Color byLIGHT (what we see) Primary Colors are: Red Blue Green Sound is an extremely important aspect of our lives. Sound travels through the air (the medium) in waves. Sound is caused by vibrations which move the medium around the wave. The sound wave which results from the vibration is a LONGITUDINAL WAVE R. Fonash The areas where the medium is squashed are called the compressions. The areas where the medium is normal are called the rarefactions. The vibration of a tuning fork leads to sound waves The sound wave vibrates the drum in the ear with the same frequency as the original vibration R. Fonash When you listen to music, the music you hear is the result of a vibrating speaker cone. * The speaker periodically pushes the air to create a longitudinal wave. * The wave travels to your ear through the medium (air). * Every actual sound you hear is a compression. * The silence between sounds is a rarefaction. R. Fonash We all know that sounds can be quiet or loud. The level of loudness of sounds is called a Decibel Scale. By establishing a uniform standard to compare sound levels, we can better understand the energy associated with different sound levels. Hearing loss will result if you experience extreme sound intensity (decibels). The speed of sound depends on the medium through which it is travelling. Sound actually travels more quickly through water than it does through air. The speed of sound in air is approximately 340m/s or 761 m/hr This speed is referred to as Mach 1 Going double this speed is referred to as Mach 2 The cone around the plane is due to air particle disturbances caused by the sound waves. The sound waves that become compressed when you reach the speed of sound are called a Sonic Boom. It is like a giant thunder clap. We already know that when waves travel they have frequency. Another word for frequency is PITCH. Heres an example of waves with high frequency and low frequency: HIGH frequency (pitch) MEDIUM frequency (pitch) LOW frequency (pitch) R. Fonash When a wave travels TOWARD you, the waves get bunched up and the frequency increases. When the wave travels AWAY FROM you, the waves get spread out and the frequency decreases. This is why you can hear the pitch of the motor change as vehicles approach you or move away from you. What does the driver hear from his frame of reference? R. Fonash For sound waves, the frequency is called pitch and the pitch will rise as the object approaches you, and fall as the object passes. For light waves, the frequency will increase as the light approaches resulting in a BLUE Shift and the frequency will decrease as the light moves away resulting in a RED Shift. This is like Astronomy and the Expanding Universe the Great Red Shift. R. Fonash Try this yourself : close you eyes and try to fill a glass of water to the top without overfilling it. Sight impaired people do this every day. They use their hearing to pick up changes in the pitch of the sound of water flowing into the glass. You can actually hear when the glass is getting full. This is the Doppler Effect. R. Fonash We usually think of light when we consider Electromagnetic Waves. However, light is only a very small part of the all the Electromagnetic waves. Other ones include Radio waves, Micro waves, X-rays, InfraRed, UltraViolet, and Gamma Rays. All of these combined make up the Electromagnetic Spectrum. FYI: InfraRed (IR) and UltraViolet (UV) waves are part of light they are just not visible to the human eye. IR waves heat up your car in the summer and UV waves burn your skin. SunBlock ads say they fight UVA & UVB R. Fonash All waves in the E/M Spectrum are transverse waves. They do not need a medium to travel through. This means that they can travel through Outer Space. Longitudinal waves such as sound cannot travel through Outer Space. In space no one can hear you scream. ALIEN R. Fonash Waves in the E/M spectrum are categorized by wavelength. Radio waves are the longest waves, Gamma waves are the smallest, and light is somewhere in the middle. R. Fonash Radio waves (AM & FM) can be as long as a city block. Microwaves are basically the width of your finger. They are great at vibrating molecules. Infrared (also called near visible waves) are reddish in nature and are interrelated with heat. Visible waves are able to be seen by humans. Ultraviolet (also called near visible waves) are just outside the visible range of waves and oriented toward the violet side of the visible range. They are dangerous to human skin. UVA and UVB X-ray waves are very small, energetic waves that can pass through less dense material. Gamma rays are very small and extremely energetic waves therefore very dangerous to humans. R. Fonash 1. ALL Electromagnetic waves have the same speed: 3.0 x 10 8 m/s (the speed of light) 1. Energy of E/M waves is not determined by the amplitude (unlike mechanical waves), but by the frequency of the wave. Low frequency waves like radio waves have the lowest energy. High frequency waves like Gamma rays have the highest energy. R. Fonash Light is only a very small part of the all the Electromagnetic waves. Other R. Fonash