Chapter 16 1 Sound sound waves longitudinal waves

Chapter 16. 1 – Sound sound waves – longitudinal waves that are caused by vibrations and travel through a material medium - sound waves carry energy through a medium - the speed of sound depends on temperature and the medium the wave travels through - higher temperature the medium – the faster the sound wave, particles move faster and collide more often

Chapter 16. 1 – Sound - denser the medium – faster the sound wave - some solids, like rubber, dampen or reduce vibrations - the loudness of a sound depends partially on the energy of the sound wave intensity – rate at which a sound wave transmits energy through a given area of a medium - intensity depends on amplitude of a wave and the distance from the source

Chapter 16. 1 – Sound - intensity is measured in decibels (d. B) - an increase of 10 d. B means that the sound is twice as loud - quietest sound humans can hear is 0 d. B - 120 d. B is the threshold of pain, hurts ears and extended exposure can cause deafness - normal conversation usually around 50 d. B

Chapter 16. 1 – Sound pitch – how high or low a sound is - depends on the frequency of a wave - high pitch, high frequency - humans can hear sounds as low as 20 Hz and as high as 20, 000 Hz infrasound – sounds lower than a human can hear ultrasound – sound with a frequency above 20, 000 Hz - dogs can hear up to 46, 000 Hz

Chapter 16. 1 – Sound how the ear hears the outer ear - sound waves pass down the ear canal to the eardrum the middle ear - the eardrum transfers the vibrations to 3 bones called the hammer, anvil, and stirrup the inner ear - the stirrup sends vibrations into the cochlea - in the cochlea the basilar membrane vibrates and stimulates hairs that send signals to nerves which go to the brain, which interprets the sound

Chapter 16. 1 – Sound musical instruments produce sound through the vibration of strings (violin), air columns (flute, trumpet), or membranes (drums) - instruments use standing waves to produce sound - the ends of the string or instrument are the nodes - changing the length of the part of the instrument that can vibrate changes the frequency the primary standing wave of an instrument has a wavelength twice the length of the instrument - that wave’s frequency is called the instrument’s fundamental frequency

Chapter 16. 1 – Sound the instrument vibrates in response to a vibrating string, air column, or membrane - the vibration of the instrument is a forced vibration - the body of the instrument has specific frequencies it will vibrate at called natural frequencies - when the string and instrument vibrate at the same frequency the sound is amplified through resonance – a phenomenon that occurs when two objects naturally vibrate at the same frequency

Chapter 16. 1 – Sound - reflected sound waves can be used to determine distances and to create images - ultrasound waves reflect off materials of different densities - the reflected images are turned into an image called a sonogram - to see an image, the wavelength must be smaller than the object being viewed - the higher the frequency, the shorter the wavelength - sonograms use frequencies of 15, 000 Hz to see objects 1 mm in size

Chapter 16. 1 – Sound sonar – sound navigation and ranging – uses acoustic signals and echoes to determine the location of objects - uses ultrasound to determine distances to the ocean floor, schools of fish, or find submarines