Sound travels through vibrations The human ear and brain hear these vibrations as sound What Is Sound Sound is a type of energy made from a vibrating source When something vibrates its particles move back and forth The particles do not move far Instead they bump into others nearby In turn those particles bump into those around them The energy gets transferred outward 6
This movement of energy is called a sound wave Unlike waves on a lake or ocean sound waves do not drift up and down Instead sound waves move back and forth like an accordion Sound waves create areas where there are many particles close together and areas where there are few particles together Not all sound waves are the same Some waves carry a lot of energy and push many particles together But just because a wave carries a lot of energy does not mean it will sound loud The person hearing the sound determines its loudness A sound may seem loud to one person and not to another A sound’s intensity is measured in 7 Silent Space Sound travels when air molecules bump into one another A vacuum is an area without air molecules Outer space is a vacuum No sound can travel there Two astronauts floating next to each other in space would not be able to hear each other even if they could speak through their thick suits Astronauts can hear one another inside spacecraft That’s because there is air inside the craft
units called decibels dB Sounds that are too intense can cause hearing loss in people Sound waves also have different frequencies Frequency is how quickly particles move back and forth Something that vibrates at a high frequency creates a high-pitched sound When something vibrates more slowly it creates a low-pitched sound Frequency is measured in units called hertz Hz A hertz equals one vibration per second The human ear can hear sounds between 20 and 20,000 Hz 8 IN THE REAL WORLD Hearing Loss In 2015 the World Health Organization WHO issued a warning It stated that 1 1 billion people from 12 to 35 years old were damaging their hearing The WHO found that many young people listen to music at unsafe levels for long periods of time Listening to music at 100 dB for longer than 15 minutes can cause hearing damage The WHO recommends keeping the volume of personal audio devices below 60 percent of the maximum volume Smartphone apps can also help monitor safe listening levels
Direction of Sound Waves Rarefaction Compression Wave Patterns This diagram shows sound waves moving through the air The yellow dots represent air particles When the particles in the wave are close together it is called a compression When they are far apart it is called a rarefaction What would the wave pattern look like if the frequency were higher What if the intensity were higher Sound waves can be arranged into patterns We control patterns of sound to communicate through speech We also create music in this way Music is the art of controlling patterns of sound Art Meets Science In the 500s BCE a Greek mathematician named Pythagoras studied music He wanted to know about the connections between music math and science 9
