5.2 Sound Study Guide Sound is a form of energy produced and transmitted by vibrating matter. Sound waves are compression (longitudinal) waves. When compression waves move through matter, the molecules of the matter move backward and forward in the direction in which the wave is traveling. As sound waves travel, molecules are pressed together in some parts (compression) and in some parts are spread out (rarefaction). The frequency of sound is the number of wavelengths in a given unit of time. The wavelength of sound is the distance between two compressions or between two rarefactions. The wavelength can be measured from any point on a wave as long as it is measured to the same point on the next wave. Sound can travel in solids, liquids, and gas (air). Sound waves must have medium through which to travel – it cannot travel in a vacuum because there is no matter for it to move through. Sound travels faster through solids because the molecules are more tightly packed. Sound travels slowest through gases. Sound waves can be absorbed, transmitted, or reflected. Pitch is determined by the frequency of a vibrating object. Objects vibrating faster have a higher pitch (higher frequency) than objects vibrating slower. Frequency is measured in Hertz. Amplitude is the amount of energy in a compression wave and is related to intensity and volume. For example, when a loud sound is heard, it is because many molecules have been vibrated with much force. Some animals make and hear ranges of sound vibrations different from those that humans can make and hear. Musical instruments vibrate to produce sound. There are many different types of musical instruments and each one causes vibrations in different ways. The basic ways to classify instruments are percussion, strings, woodwind instruments, brass, and electronic instruments. Vocabulary Absorbed – sound waves can be trapped or broken up by substances and are unable to travel farther Acoustics – the science of sound amplitude – amount of energy in a compression wave, it is related to intensity and volume crest – the highest point of a wave communication tools – the various ways sound waves are used (musical instruments, voice, animal sounds, Morse Code, and telephone) compression – where a sound wave pushes matter together decibel – how the loudness of a sound is measured (dB) Doppler effect – change in the apparent frequency of a wave, because either the source of the wave is moving toward or away from the observer, or the observer is moving toward or away from the source of the wave (car blowing its horn as it passes a person on the street) echo location – animals such as bats and dolphins use this by bouncing sound off objects to determine distance frequency – the number of vibrations in a given unit of time; how fast an object vibrates (measured in Hertz, Hz) Morse Code – a series of long and short signals standing for letters of the alphabet that are sent over wires pitch – how high or low a sound is as determined by the frequency of a vibrating object (Objects vibrating faster have a higher pitch than objects vibrating slower. Larger objects vibrate more slowly and have lower pitch than smaller objects.) rarefaction – where a sound wave spreads matter apart reflected – sound waves can bounce of a surface resonance – the amplification of sound by increasing the force of its vibration (when a plucked guitar string causes the entire body of the guitar to vibrate) sonar –a device that reflects sound by sending out high frequency sound waves and recording the time it takes to return to the source sound – a form of energy produced and transmitted by vibrating matter transmitted – sound waves can travel through a material trough – the lowest point of a wave ultrasound – a device used by doctors to see inside the body by using sound waves to bounce off such things as bone, muscle, or organs vibration – the rapid back-­‐and-­‐forth motion of an object wave – a disturbance moving through a medium (solid, liquid, or gas) wavelength -­‐ the distance between two compressions Big Idea Questions  How is sound made?  How can you use a Slinky toy to demonstrate compression waves?  Explain wavelength in regard to sound.  How does the amplitude of sound waves relate to their intensity?  How are the amplitudes of sound waves and water waves related?  If an object vibrates quickly, how will that affect the frequency and pitch of the sound? Give some examples of objects you could use to prove your answer.  Why can sound only travel where there is matter to transmit the sound?  Describe how sound travels differently through solids, liquids, and gases.  Can sound travel in outer space? Why or why not?  Describe the ways in which the following musical instruments make sound: drum (percussion), violin (string), trumpet (brass), and flute (woodwind).  How can you control the frequency of sound when you are playing a musical instrument? Choose one instrument, and explain.  Give some examples of how you use sound in your daily life. How is sound helpful for safety?  Can too much sound be dangerous? Explain your answer.