17 - Weebly
Wave Properties:
Objectives:
• Define mechanical waves and relate waves to energy
• Describe transverse, longitudinal, and surface waves and discuss how they are produced
• Identify examples of transverse and longitudinal waves
• Analyze the motion of a medium as each kind of mechanical wave passes through it
Waves carry energy from one place to another
Mechanical waves move energy through matter called a medium
The wave causes a disturbance in the medium
So, a mechanical wave is created when a source of energy causes a vibration that travels through a medium
There are three main types of mechanical waves:
1. Transverse waves – causes the medium to travel at right angles to the direction in which the wave travels
highest point from resting
lowest point from resting
2. Longitudinal waves – causes the medium to travel parallel to the direction in which the wave travels
3. Surface waves – a wave that travels along
a boundary separating two mediums
Can be a combination of perpendicular (transverse)
and parallel (longitudinal)
Properties of Mechanical Waves
Objectives:
• Define frequency, period, wavelength, and wave speed and describe these properties for different kinds of waves
• Solve equations relating wave speed to wavelength and frequency or period
• Describe how to measure amplitude and relate amplitude to the energy of a wave
Period - the time required for one cycle (crest to crest OR trough to trough)
Frequency – the number of cycles in a give unit of time
Measured in cycles per second = hertz
Wavelength –
Transverse is the distance between a point on one wave and the same point on the next wave
Longitudinal is the distance between adjacent compressions or rarefactions
Speed of wave = frequency x wavelength ( = ((
Speed of wave = wavelength/period ( = (/T
Units: speed = m/s frequency = hertz wavelength = m period = s
Amplitude – The maximum displacement of a medium from its rest position
The more energy a wave has, the greater the amplitude
Objectives:
• Describe how reflection, refraction, diffraction, and interference affect waves
• State a rule that explains refraction of a wave as it passes from one medium to another
• Identify factors that affect the amount of refraction, diffraction, or interference
• Distinguish between constructive and destructive interference and explain how standing waves form
Reflection occurs when a wave bounces off a surface that it cannot pass through
Reflected wave is flipped upside-down when it returns
Refraction occurs when a wave bends as it enters a medium
One side of the wave moves slower than the other side of the wave causing the bend
Diffraction occurs when a wave bends around an obstacle or passes through a narrow opening
Diffraction is greater if the wavelength is greater than the obstacle or opening
Interference occurs when two or more waves overlap or combine with one another
Crest align with crest: Crest align with Trough:
Two or more waves combine to produce a Two or more waves combine to produce a
wave with a larger displacement wave with a smaller displacement
Standing waves occur when incoming and reflected waves pass through each other
The resulting wave appears to stay in one place
Node is a point on the standing wave that has no displacement
Antinode is a point on the standing wave that has the greatest displacement
Objectives:
• Describe the properties of sound waves and explain how sound is produced and reproduced
• Describe how sound waves behave in applications such as ultrasound and music
• Explain how relative motion determines the frequency of sound an observer hears
• Analyze the functions of the main regions of the human ear
Properties of sound waves include speed, intensity/loudness, and frequency/pitch
Speed – sound travels faster in solids, slower in liquids, and the slowest in gases
Speeds depends on the density and elasticity of the medium
Intensity – rate at which a wave’s energy flows through a given area
Unit = decibel (dB)
Decibel is based on powers of ten = for every 10 dB, the intensity goes up 10 times
Example: a 20 to 40 dB increase in sound is 100 times louder than 20 alone
Loudness – is the physical response to the intensity of sound depending on the health of ears
Frequency – depends on how fast a wave is moving
Pitch is the perceived frequency of a sound wave depending on the health of ears
Ultrasound – sounds waves with frequencies below human hearing
humans hear between 20Hz and 20,000Hz
Used in medical procedures
Sonar – Sound Navigation and Ranging – used to find depths in the ocean
Distance is determined by taking the speed of sound in water
divided by time takes for wave to travel to a surface
Doppler Effect – Sound travels in waves but moving objects with compress waves in front of the moving object and stretches out the wave behind the moving object
• When the object moves toward listener, sound has a higher pitch and intensity
• When the object moves away from listener, sound has a lower pitch and intensity
Hearing and the Ear: depends on three sections of the ear
Outer ear: ear canal, eardrum
Middle ear: hammer, anvil, stirrup
Inner ear: cochlea, nerve cells, auditory nerve
Reproducing sound is done by converting sound waves to electronic signals that can be processed and stored and converted the electronic signals back into sound waves
Music is made when standing waves are produced from interference
Musical instruments change the frequencies of waves which change pitch
Resonance occurs when standing waves responds to another standing wave of the same frequency
Musical instruments change pitch by changing frequency
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area where particles of medium are the closest
Rarefaction – area where particles of medium are spread out
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