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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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