Vibrations+and+Waves

__Unit 4- Vibrations and Waves__ __Vibrations of a pendulum__ __**WAVE** Description__ __Parts of a Wave__ > Radar and Microwave Ovens operate at gigahertz __Wave motion__ >> -the air molecules themselves do no move, but they are medium through which the energy of sound waves travel > //The energy transferred by a wave from a vibrating source to a receiver is carried by a disturbance in a medium// __Wave speed__ __Interference__ __Doppler Effect__ __Light__ __Blue/Red Shifts__ __Bow Waves__ __Shock Waves__
 * A repeating, back-and-forth motion about an equilibrium position is a vibration.
 * A vibration canot exist in one instant.
 * It needs time to move back and forth.
 * A disturbance that is transmitted progressively from one place to the next with no actual transport of matter is a **WAVE**.
 * A wave cannot exist in one place but must extend from one place to another.
 * Light and sound are both forms of energy that move through space as waves.
 * A pendulum is a weight at the end of a string/cord/bar/stick/etc. that is allowed to swing back and forth.
 * The end without the weight is attached to some fixed point.
 * The regularity that some pendulum's swing with allowed them to be used as parts of clocks.
 * Galileo discovered that the time a pendulum takes to swing back and forth through small angels depends on the length of the pendulum, not on the mass.
 * Long pendulum = longer period
 * In other words, it swings back and forth more slowly (less frequently) than a shorter pendulum.
 * When we walk, we let our legs swing with the help of gravity, like a pendulum. A person with long legs tends to walk with a slower stride than a person with shorter legs. This is also noticeable in long legged animals such as giraffes and horses, which run with slower gait than short legged animals such as hamsters and mice.
 * The back and forth vibratory motion of a pendulum is called **SIMPLE HARMONIC MOTION.**
 * If the pendulum is suspended above a moving conveyor belt with a writing device on the bottom of the pendulum, it will sketch a **SINE CURVE**.
 * Like a water wave, the high points of a wave are called the **CRESTS**
 * The low points of the wave are called the **TROUGHS**
 * The line the middle is called the **MIDPOINT** of the vibration
 * **Amplitude** = the distance from the midpoint to the crest (or trough)
 * **Wavelength** = the distance from top of one crest to top of the next (or from trough to trough)
 * **FREQUENCY** - the number of vibrations an object in a specified unit of time
 * a complete back and forth vibration is one **CYCLE**
 * the unit for frequency is the **HERTZ**
 * one cycle per second is 1 hertz, 2 cycles = 2 hertz and so on
 * **higher frequencies are measured in kilohertz (kHZ) -** thousands of cycles per second, megahertz (MHz)- millions of cycles per second, or gigahertz (GHz)- billions of cycles per second
 * AM (Amplitude Modulation) radio waves are broadcast in kilohertz, and different stations are determined by changing the amplitude, not the frequency
 * FM (Frequency Modulation) radio waves are broadcast in megahertz, and different stations are determined by changing frequency
 * Most of the information around us get to us in some way of wave
 * **Sound** = energy that travels to our ears in form of a wave
 * **Light** = energy that travels to our eyes in the form of a different kind of wave (electromagnetic)
 * Signals that reach our radio and television sets also travel in the form of electromagnetic waves
 * When energy is transferred by a wave from a vibrating source to a receiver, no transfer of matter occurs to visualize this, take the end of a string/rope/sheet/garden hose/power cord/etc.
 * Sake it to make a wave
 * Watch the wave go through it to the other end
 * Energy was transmitted from your hand to the other end, but no matter was moved from one end to the other
 * Another example - drop a pebble in a body of water, watch the wave move from the center of the point the pebble entered
 * In this example too, it is the disturbance that moves, not the water
 * After the disturbance, the after remains where it was before
 * Another example - when someone talks to you, sound is a disturbance of the air molecules between their mouth and your ears
 * to sum it up -
 * The speed of a wave depends on the medium through which is moves
 * Sound waves travel at speeds of form 330 meters per second to 350 m/s (depending on temperature)
 * Sound waves travel about 4 times that in water
 * You can calculate the speed of a wave by multiplying the wavelength by the frequency
 * Transverse Waves
 * Suppose you create a wave along a rope by shaking the free end up and down
 * The motion of the rope is at right angles to the direction in which the wave is moving
 * Whenever the motion of the medium is at right angles to the direction in which a wave travels, the wave is a **TRANSVERSE WAVE**
 * Waves in the stretched strings of musical instuments and the electronmagnetic waves that make up radio waves and light are transverse.
 * Longitudinal waves
 * Sometimes the particles of the medium move back and forth in the same direction in which the wave travels
 * When the particles oscillate parellel to or along the direction of the wave rather than at right angels to it, the wavve is **LONGITUDINAL WAVE**
 * Sound waves are longitudinal waves
 * two pieces of matter cannot occupy the same space at one time, but two waves can
 * If you drop two rocks in water, the waves produced by each can overlap and form an interference pattern
 * An interference pattern is a regular arrangement of places where waves effects are increased, decreased, or neutralized
 * **Constructine interference** = when the crest of one wave overlaps the crest of another wave and their individual effects add together
 * **Destructive interference** = when the crest of one wave overlaps with the trough of another, so their effects are reduced, sometimes canceled
 * In an interference pattern, the dark and light areas are where crests and troughs of the waves are in phase with each other
 * The gray areas are where troughs are meeting with crests, and the waves are out of phase with each other
 * Interference is characteristic of all wave motion, whether the waves are water waves, sound waves, or light waves
 * If you tie a rope to a wall, then shake the rope to produce a wave, the wall is too rigid to vibrate, so the wave is sent back through the rope in the opposite direction
 * When it is done just right, a standing wave will be created
 * A **STANDING WAVE** is one where the wave appears to stay in place, not to move through the medium
 * **NODE** - the part of standing wave that remains stationary
 * With the rope on the wall, if you get a standing wave going, you could put your fingers on either side of the rope at the nodes and it will not touch them
 * In between the nodes are the areas with the largest amplitude, the **ANTINODES**
 * Standing waves are the result of the interference the nodes are the stable regions of destructive interference
 * You can produce a variety of waves by shaking the rope at different frequencies
 * //A standing wave forms only if half a wavelength or a multiple of half a wavelength fits exactly into the length of the vibrating medium//
 * Standing waves are set up in the strings of musical instruments that are struck
 * Standing waves can be produced in either transverse or longitudinal waves
 * Imagine a bug jiggling and bobbing up and down in the middle of quite puddle
 * Suppose the bug is just sitting there in one place, treading water the crestes are all connected as a circle, because the wave speed is the same in all directons
 * Now suppose that bug moves across the water at a speed less than the wave speed
 * In effect, the bug is chasing the crest of the wave it created
 * The wave pattern will no longer be concentric
 * The waves will be closer together ahead of the bug, and farther apart behind the bug
 * As a wave source approaches, an observer encounters waves with a higher frequency
 * As the wave source moves away, the observer encounters waves with a lower frequency
 * This apparent change in frequency due to the motion of the source (or reciever) is called the Doppler Effct (named after Christian Doppler- Austrian scientist)
 * Sound
 * The Doppler effect is evident when you hear the changing pitch of a siren as a fire truck approaches you
 * When the fire truck approaches, the pitch sounds higher than normal, because the sound wave crests are encountering you more frequently
 * When the truck passes you and moves away, the pitch drops, because the sound wave crests are encountering you less frequently
 * Police Radar
 * Police make use of the Doppler Effect in radar waves
 * Radar waves are higher in frequency than radio waves, but lower than light waves
 * the officer aims the radar at the vehicle
 * The computer in the radar measures the waves bounced off the vehicle and compares it to the waves from the radar
 * Bats hunt insects in the dark by using the Doppler effect and echo location
 * Some moths are covered by a thick covering of fuzzy scales that deaden the echos
 * The Doppler effect also occurs for light
 * When the light source approaches, the frequency increases(blue shift)
 * When the light source recedes, the frequency decreases(red shift)
 * The shifts are named according to the visible light spectrum **ROYGBIV**
 * As a rapidly spinning star spins, the side spinning away from the earth, there is the red shift, and the side spinning towards earth is the blue shift, allowing astronomers to measure the rate of spin
 * Also being measured by the red/blue shift are entire galaxies, as they move away from us, they are shifted in the red
 * When the speed of the source of the wave is as fast as the wave speed, something interesting happens, the waves pile up
 * When an airplane travels at the speed of sound, the sound waves pile up in front of the airplane, disrupting the flow of air over the wings, making it difficult to control the airplane
 * When the plane travels faster than the speed of sound(**SUPERSONIC**), it flies in front of the sound waves, making it much easier to fly, no sound waves interfering with the airflow
 * A shock wave occurs when an object moves faster than the speed of sound
 * A shock wave is a 3-Dimensional wavw that consists of overlapping spheres that form a cone
 * A common misconception is that sonic "boom"s are only produced the instant that an airplane breaks the sound barrier
 * The fact is that a shock wave and the resulting "boom" are swept continuously behind an aircraft while it is travelling supersonic
 * It is not necessary for an object to produce sound to break the sound barrier
 * The fact that an object is moving faster than sound creates sound
 * A supersonic bullet passing overhead will produce a small sonic boom
 * The larger the bullet, the bigger the boom
 * Cracking a whiip is a small sonic boom
 * Snapping a also a small sonic boom