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

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

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 intererence? 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

17.4 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 Three ways to transfer heat energy Why is conduction slower in gas than in a liquid and solids? Three ways to transfer heat energy Conduction – two objects must be in contact Because of collisions between the particles Slower in gases than in liquids and solids because the particles are farther apart Don’t collide as often