Sound

• Stringed instruments are plucked or bowed to make them vibrate.
• Wind instruments have an air column to make them vibrate.
• Percussion instruments are played and make vibrations by striking them.
• Sounds travel through the air as vibrations.
• When sound vibrations reach your ear, they cause your eardrums to vibrate.
• Vibrations are transmitted inwards to the inner ear where they are converted into electrical signals which pass to the brain.
• Sound vibrations cause part of the microphone to vibrate. These vibrations are converted to a varying electrical current which has the same pattern as the vibrations of the sound.
• The speed of sound in the air is about 330 m/s
• After you shout, you may hear an echo. The sound has reflected from the hard surface and back to your ears.
• One way to measure the speed of sound in the lab is to find out how long a sound takes to travel a measured distance.
• An echo is heard when a sound reflects off a hard surface such as a large wall.
• The speed of sound changed if the temperature of the air changes, if it is more humid, ect.
• An image of musical notes can be produced by playing an instrument next to a microphone connected to an oscilloscope. The mic receives the vibrations and converts them into an electrical signal.
• A signal generator can produce pure notes that have a very simple shape when displayed on an oscilloscope screen.
• The time to complete one vibrations is know as the period of the vibration.
• Frequency is measured in hertz. 1 Hz is one vibration per second.
• With a low frequency note, thrtr id.
• With a low frequency note, there is a single dot which moves across the oscilloscope screen.
• Amplitude increases as volume increases.
• Higher pitch means higher frequency.
• Humans can hear notes ranging from about 20 Hz to 20,000 Hz.
• Vibrations traveling through a material - the particles of the material or alternately compressed together and then rarefied as the sound passes through.
• Sound as a wave - a smoothly varying up and down line, like the trace of an oscilloscope screen.
• The areas of the sound wave where air molecules are closer together are called compressions.
• In between each compression, there are rare fractions, areas in which air molecules are less closely pack together or rarefied.
• Wave represents the changes in air pressure as sound travels from its source.