Block 3 physics of waves.ppt

Uses of ultrasound Medicine: Observing soft tissue damage – ultrasound can image the digestive tract and can be used to break down dangerous accumulations of minerals such as kidney stones infrasound Sounds below 20Hz are too low to hear , and are known as infrasound * 12.4 How sounds travel * * * Copy then hand out white boards for the following quiz type slides. Could copy this one down if time * Check out what they can hear at / If you dont have a frequency generator at hand. * Block 3 physics of waves sound * * 12.1 making sound String instruments Wind instruments Percussion instruments Tuning fork In each case ,part (or all) of the instrument is made to vibrate. This cause the air nearby to vibrate ,and the vibrations travel through the air to the audience’s ears. * Sounds travel through the air as vibrations. These vibrations can travel through any material---solid , liquid ,gas * 12.2 AT THE SPEED OF SOUND * The speed of sound depends on the material through which it is passing. It is greater in solids than in liquids or gases. * Sound travels by particles vibrating. To understand this better you need to remember what the particles look like in a solid, liquid and a gas: solid liquid gas In which state are the particles closest together? In which state are the particles furthest apart? solid gas Which state does sound travel fastest through? Why? Sound travels fastest through solids because the particles are closer together than in a liquid and a gas, so the vibrations are more easily passed from particle to particle. Speed of Sound Air (330 metres per second) Water (1500 metres per second) Wood (3850 metres per second) How fast? Different material ,different speed Speed of Sound Sound in a Vacuum Can we hear the bell ? why? echo * Measuring the speed of sound * 12.3 seeing sounds * oscilloscope * An image of the notes can be produced by playing the instrument next to a microphone connected to an oscilloscope. What are waves? Waves transfer energy They