What causes mechanical waves? List four different examples of mechanical waves (just think of waves). Bring Digital Cameras

Mechanical Waves and Sound Chapter 17 Mechanical Waves and Sound SPS9 Students will investigate the properties of waves Recognize that all waves transfer energy Relate frequency and wavelength to the energy of different types of electromagnetic waves and mechanical waves. Relate the speed of sound to different mediums. Explain the Doppler Effect in terms of everyday interactions.

17.1 Mechanical Waves What causes mechanical waves? What are the three main types of mechanical waves?

17.1 Mechanical Waves What causes 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 Waves What are the three main types of mechanical waves? Mechanical waves are classified by how they move through a medium

17.1 Mechanical Waves What 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 Waves What 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 Waves What 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

17.2 Properties of Mech. 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 How are frequency, wavelength, and speed related? 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. Waves What determines the frequency of a wave? 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. Waves How are frequency, speed and wavelength related? The wave equation v = speed of the wave (m/s) f = frequency (Hz) l = wavelength (m) Frequency and wavelength are inversely proportion When one increases, the other decreases v=fl

17.2 Properties of Mech. Waves What determines the frequency of a wave? 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? v=(2.0Hz)(2.0m) v=4 m/s v=fl l = 2.0 m f = 2.0 Hz

17.2 Properties of Mech. Waves What determines the frequency of a wave? 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? 5 m/s=(10 Hz)l l=0.5 m v=fl v = 5 m/s f = 10 Hz

S-51 What determines the frequency of a wave? A sound wave with a speed of 345 m/s has a wavelength of 25 m. What is the frequency of the wave?

S-52 What 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?

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

17.3 Behavior of Waves 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 How does reflection change a wave? 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 Waves What causes the refraction of a wave when it enters a new medium? 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 Waves What are two types of interference? 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 Waves What are two types of interference?

S-53 What 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-54 What is refraction? Where does refraction occur? What causes the refraction of a wave when it enters a new medium? What is refraction? Where does refraction occur? Give one example of refraction.

17.4 sound and Hearing 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 What properties explain the behavior of sound? 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 Hearing Frequency Interpreted as Pitch What properties explain the behavior of sound? Frequency Interpreted as Pitch High frequency – high pitch Low frequency – low pitch Depends some on age and health

17.4 Sound and Hearing How does frequency of sound change for a moving source? 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 Hearing Three main regions of the ear What are the functions of the three main regions of the ear? 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

S-54 Name the three main parts of the ear and their functions. What are the functions of the three main regions of the ear?? Name the three main parts of the ear and their functions.

S-55 What is the Doppler Effect? Give one example. How does frequency of sound change for a moving source? What is the Doppler Effect? Give one example.

S-56 Wet Cat! Test Day! Yah!