Sound is a Longitudinal Wave particles vibrate parallel to the direction of the motion of the wave
Terminology Compressions: areas where particles come closer together Rarefactions: regions where particles are further apart http://surendranath.tripod.com/Applets/Waves /LWave01/LW01.html
Vibrations are the source of all sound, whether they are visible or invisible Visible vibrations – Speaker, guitar strings, etc Invisible vibrations – Air molecules (blowing over bottle), tuning fork, etc.
Tuning Fork/Strobe Light Demo When a tuning fork vibrates, the tines move in and out creating longitudinal waves in air Sound depends on the quality of vibration
If a compression hits your ear drum, – The pressure from outside your ear drum pushes your ear inwards If a rarefaction hits your ear drum – Pressure from inside your ear pushes your ear drum outwards As your ear drum moves in and out, your brain interprets the movement as sound
Range of Human Hearing Humans can typically hear an audible range of sound for 20 Hz and 20,000 Hz This breaks down as: – You get older – You listen to really loud music (concerts, etc) Frequencies greater than 20kHz are ultrasonic Frequencies less than 20 Hz are infrasonic
Sound Technologies Sonar – Uses sound to detect things underwater – Process called echolocation – by analyzing echoes (reflected sound) we can detect objects
Echolocation – Bats and dolphins use echolocation to find prey and locate things around themselves
Sound Needs a Medium! Sound always needs a medium to travel through (in space, no one can hear you scream) Medium can be air, water (hear a boat approaching underwater), steel (put your ear to a train track), etc. The more densely packed the medium, the faster the speed of sound The larger the amplitude of the sound wave, the louder the sound
Pitch the human perception of the highness or lowness of sound depends on the frequency of sound Big distinction between pitch and frequency is that above 20,000 Hz the pitch of the sound doesn’t exist because the human ear can’t detect it
Questions 1)Provide a brief description of how sound travels through the air and interacts with your ear. Use the terms: longitudinal, compression, refraction, ear drum and medium. 2)Describe the pitch of the sound that you would hear at 30Hz and 19000 hz. 3)If you were placed in a vacuum with a friend. He starts screaming at a constant volume and frequency. As the air was removed from the vacuum, how would the sound you hear change? Explain. 4)In space there is no air so astronauts use radio waves to communicated with each other. If the radio breaks, what could astronauts do to communicate with sound?