• List four different examples of mechanical waves (just think of waves).

Bring Digital Cameras

S-50What causes mechanical waves?

SPS9 Students will investigate the properties of wavesa. Recognize that all waves transfer energyb. Relate frequency and wavelength to the energy of different types of

electromagnetic waves and mechanical waves.e. Relate the speed of sound to different mediums.f. Explain the Doppler Effect in terms of everyday interactions.

Chapter 17

Mechanical Waves and Sound

What causes mechanical waves?What are the three main types of mechanical waves?

17.1 Mechanical Waves

• Mechanical wave – disturbance in matter that carries energy from one place to another– Medium – material that a mechanical

wave travels through– Required– A source of energy must cause a

vibration in the medium

17.1 Mechanical WavesWhat causes mechanical waves?

• Mechanical waves are classified by how they move through a medium

17.1 Mechanical WavesWhat are the three main types of mechanical waves?

• Transverse Wave - the medium vibrates perpendicular to the direction the energy is going– Part

• Crest – highest point• Trough – lowest point• Equilibrium – resting point (when there is no

wave)• Amplitude – the distance from equilibrium to

crest or trough• Wavelength – distance from one point to the

same point on the next wave

17.1 Mechanical WavesWhat are the three main types of mechanical waves?

• Longitudinal Wave – vibration is parallel to the direction the energy flows– Parts– Compression – particles are the closest

together– Rarefaction – particles are the farthest

apart– Wavelength – the distance from one

point on a wave to the same point on another

17.1 Mechanical WavesWhat are the three main types of mechanical waves?

• Surface Wave – travels along the boundary between two mediums– Circular motion of the particles– Combines actions of longitudinal and

transverse waves

17.1 Mechanical WavesWhat are the three main types of mechanical waves?

What determines the frequency of a wave?How are frequency, wavelength, and speed related?How is the amplitude of a wave related to the wave’s energy?

17.2 Properties of Mech. Waves

• Period – the time for one complete cycle– Frequency – the number of complete

cycles per second – Measured in hertz (Hz)– Determined by how fast the source of

the wave vibrates

17.2 Properties of Mech. WavesHow are frequency, wavelength, and speed related?

• Wavelength – distance from one point on a wave to the same point on the next wave

• Wave Speed – how fast energy is transferred by a wave– Sound 345 m/s– Light 300,000,000 m/s

17.2 Properties of Mech. WavesWhat determines the frequency of a wave?

• The wave equation

– v = speed of the wave (m/s)– f = frequency (Hz)– = wavelength (m)

• Frequency and wavelength are inversely proportion– When one increases, the other decreases

17.2 Properties of Mech. WavesHow are frequency, speed and wavelength related?

v=f

• Practice problem 1

• A wave on a rope has a wavelength of 2.0 m and a frequency of 2.0 Hz. What is the speed of the wave?– Variables?– Fill in the equation?– Answer?

17.2 Properties of Mech. WavesWhat determines the frequency of a wave?

v=f

= 2.0 m f = 2.0 Hz

v=(2.0Hz)(2.0m)

v=4 m/s

• Practice problem 2

• What is the wavelength of an earthquake wave if it has a speed of 5 m/s and a frequency of 10 Hz?– Variables?– Fill in the equation?– Answer?

17.2 Properties of Mech. WavesWhat determines the frequency of a wave?

v=f

v = 5 m/s f = 10 Hz

5 m/s=(10 Hz)

=0.5 m

• A sound wave with a speed of 345 m/s has a wavelength of 25 m. What is the frequency of the wave?

S-51What determines the frequency of a wave?

• A wave of light has a speed of 300,000,000 m/s. What is the wavelength of a wave with a frequency of 450,000,000 Hz?

S-52What determines the frequency of a wave?

• Amplitude – the maximum displacement from the rest position– Amplitude is directly related to energy– Larger amplitude means more energy– Think of a tidal wave

• A really huge wave does much more damage than a small wave

17.2 Properties of Mech. WavesHow is the amplitude of a wave related to the waves energy?

How does reflection change a wave?What causes the refraction of a wave when it

enters a new medium?What are two types of interference?

17.3 Behavior of Waves

• Reflection – when a wave bounces off a boundary between mediums– Does not change the speed of a wave– Does not change the frequency of a

wave– Can be flipped upside down

17.3 Behavior of WavesHow does reflection change a wave?

• Refraction – the bending of a wave as it enters a new medium– Because one side of the wave moves

slower than the other– Slows down, angle becomes smaller– Speeds up,

angle becomes greater

17.3 Behavior of WavesWhat causes the refraction of a wave when it enters a new medium?

• Interference – when two or more waves overlap and combine– Constructive – the waves combine to

make a greater amplitude– Destructive – the waves combine to

make a smaller amplitude– Graphically – add the amplitudes

together• Above equilibrium is positive• Below equilibrium is negative

17.3 Behavior of WavesWhat are two types of interference?

17.3 Behavior of WavesWhat are two types of interference?

• Draw a wave that has a wavelength of 6 squares, and an amplitude of 4 squares.

• If it went through constructive interference with an identical wave,

what would be the maximum

amplitude reached?

S-53What are two types of interference?

• What is refraction?• Where does refraction occur?• Give one example of refraction.

S-54What causes the refraction of a wave when it enters a new medium?

What properties explain the behavior of sound?How does the frequency of a sound change for a

moving source?What are the functions of the three main regions of the

ear?

17.4 sound and Hearing

• Intensity – the rate of energy flow– Increases with the energy of the source– Decreases rapidly with distance from

source– Measured in decibels (db)– Interpreted as Loudness

• Subjective – subject to a persons interpretation

17.4 Sound and HearingWhat properties explain the behavior of sound?

17.4 Sound and HearingWhat properties explain the behavior of sound?

• Frequency– Interpreted as Pitch

• High frequency – high pitch• Low frequency – low pitch

– Depends some on age and health

• Doppler effect – a change in frequency caused by motion of the sound source, listener, or both.– Approaching sounds are higher in

frequency– As the source moves away sounds are

lower in frequency

17.4 Sound and HearingHow does frequency of sound change for a moving source?

• Three main regions of the ear– Outer ear (external ear, ear canal, ear

drum)• Gathers and focuses sound

– Middle ear (3 bones – hammer, anvil, stirrup)• Receives and amplifies vibrations

– Inner ear (cochlea)• Nerves sense vibrations and send signal to

brain

17.4 Sound and HearingWhat are the functions of the three main regions of the ear?

• Name the three main parts of the ear and their functions.

S-54What are the functions of the three main regions of the ear??

• What is the Doppler Effect? • Give one example.

S-55How does frequency of sound change for a moving source?

S-56Wet Cat!

Test Day!

Yah!