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# Waves and vibrations

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### Waves and vibrations

1. 1. What is a wave? A disturbance that moves through matter or space. Energy moving from place to place. The matter or space that the wave travels through is called a medium
2. 2. Classification of waves There are two main categories of waves:1. Mechanical Waves (our focus now ) ~ Require a medium in order to transport their energy from one location to another. ~ Ex: Sound2. Electromagnetic Waves (we will look at these in more detail next week) ~ EM waves are capable of transmitting energy through a vacuum (i.e., empty space). ~ Ex – Photons of light
3. 3. Mechanical Waves  Two types of waves: 1. Longitudinal (aka Compressional)•Longitudinal waves look like a slinky•Direction of medium is parallel to the direction of wavepropagation (motion)•Ex: Sound Waves - move air back and forth
4. 4. Characteristics of a Longitudinal Wave 2 areas Compression- an area of high molecular density and pressure Rarefaction - an area of low molecular density and pressure
5. 5. Mechanical Waves  Two types of waves: 2. Transverse•Transverse waves look like a sine curve•Direction of medium is perpendicular to direction of wavepropagation (motion)•Ex: Water Waves - move stick up and down in a pond
6. 6. Characteristics of a Transverse Wave 1)Crest- highest position Crest of the wave 2) Trough- lowest position of the wave 3) Wavelength- the distance between two ‘like’ points on a wave (crest to crest; trough to trough) 4) Amplitude- Height of Trough the wave (from origin to crest or trough) 5) Frequency- The number of crests that pass by a point each second.
7. 7. Measuring a Wave Frequency vs. Period Frequency is how many  Period is the number of waves pass by you (or an seconds (usually it’s less than arbitrary point) per 1 second) it takes for 1 WAVE second, measured in to pass by you, measured in Hertz. seconds or seconds per wave. 1 1 f T T f
8. 8. Measuring a Wave Wave motion compared to linear motion Wavelength is comparable to displacement Period is comparable to time To find linear speed you use the equation: distance speed time v f To find wave speed do the same thing, just with wave variables: wavelength( ) wave speed (v) period ( ) Since frequency is the inverse of period you will usually see the equation : wave speed = wavelength x frequencyUnits: Since a “cycle” is not a standard unit this gives you m/s.
9. 9. Stan and Anna are conducting a slinky experiment. They are studyingthe possible affect of several variables upon the speed of a wave in aslinky. Their data table is shown below. Fill in the blanks in the table. Medium Wavelength Frequency Speed Zinc, (1.75)(2)= 3.5m/s 1.75 m 2.0 Hz ______ 1-in. dia. coils Zinc, (0.9)(3.9)= 3.51m/s 0.90 m 3.9 Hz ______ 1-in. dia. coils Copper, (1.19)(2.1)= 2.499m/s 1.19 m 2.1 Hz ______ 1-in. dia. coils Copper, 0.60 m 4.2 Hz (0.6)(4.2)= 2.52m/s ______ 1-in. dia. coils Zinc, (0.95)(2.2)= 2.09m/s 0.95 m 2.2 Hz ______ 3-in. dia. coils Zinc, (1.82)(1.2)= 2.18m/s 1.82 m 1.2 Hz ______ 3-in. dia. coils