Presented by Kesler Science Sound Waves Created by Kesler Science – More 5E lessons at KeslerScience.com Presented by Kesler Science

Essential Questions: What is sound? How do sound waves travel? How do physical properties of a medium affect the speed of sound waves? What properties of waves affect what we hear? What is the Doppler effect?

Sound Waves Sound Vibrations that travel through the air or other media When these vibrations reach the air near your ears you hear the sound.

Quick Action – Sound Waves Think about this riddle. If a tree falls in a forest and no one is there to hear it, does the falling tree make a sound? Discuss this with a partner. Must you hear a vibration for it to be sound? Is the energy produced by the vibration a sound if no one hears it? Write your own definition for sound.

How Sound Travels Sound Waves Sound waves carry energy through a medium (solid, liquid or gas) without the particles of the medium traveling along. Sound travels as a longitudinal wave.

How Sounds are Made Sound Waves Longitudinal waves are generated when a source of energy forces the matter in a medium to vibrate. This back-and-forth motion pushes air particles together, generating a compression, or moves the particles apart, generating a rarefaction. Compression Rarefaction

Quick Action – Sound Waves Together with a partner make a list of things that you use daily that make sounds. Choose one of these objects and try to figure out how it makes vibrations. Here is an example: When you strike a drum you cause the drumhead to push inward. The drumhead then rebounds in the opposite direction. Each movement creates compressions and rarefactions. Be prepared to share with the class.

Medium Sound Waves Sound waves must have a medium to travel through. Gas – air is the most common Liquid Solid In outer space there are no molecules to compress or rarefy, so sound does not travel through outer space.

Speed of Sound Sound Waves Depends on the physical properties of the medium it travels through. Elasticity Density Temperature At room temperature, sound travels through air at about 342m/s. Speed of Sound Medium Speed(m/s) Gases Air (0o C) 330 Air (20oC) 342 Liquids Fresh water 1,490 Salt water 1,530 Solids (25oC) Hard wood 4,000 Glass 4,540 Steel 5,200

Physical Properties of Media Sound Waves Physical Properties of Media Elasticity – the ability of a material to bounce back after being disturbed Solid materials are usually more elastic than liquids or gases. Particles of a solid do not move very far, so they bounce back and forth quickly as the vibration travels through the object, which allows waves to move faster. Liquid Gas Distance traveled in 1 sec. Solid

Quick Action – Sound Waves Write About Look back at the previous slide. Compare the speed of waves in solids, liquids and gases. Explain in your own words how elasticity affects the speed of sound waves. 2 min. … go!

Physical Properties of Media (cont.) Sound Waves Physical Properties of Media (cont.) Density – how much matter there is in a given amount of space The speed of sound depends on how close together the particles of the substance are in the medium. Speed of Sound Medium Speed(m/s) Density Gas Least dense Air 342 Liquid Fresh water 1,490 Solid Steel 5,200 Most dense This can become confusing to middle school students as particle size in relation to density can slow sound waves. So just talk about how sound waves move faster in solids and slower in gases.

Physical Properties of Media (cont.) Sound Waves Physical Properties of Media (cont.) Temperature - degree or intensity of heat present in a substance or object In a given media (solid, liquid, gas), sound travels more slowly at lower temperatures. Air Temperature (oC) Speed (m/s) -20 318 -10 324 330 10 336 20 342 30 348

Properties of Sound Waves Intensity Loudness Frequency Pitch

Properties of Sound Waves Intensity – the amount of energy the wave carries per second through a unit of area Amplitude increases with increased energy Measured in watts per square meter (W/m2)

Properties of Sound Waves (cont.) Loudness – describes what you actually hear. Though not the same as loudness, the greater the intensity of a sound wave, the louder it is. Measured in decibels (dB) Maximum safe level is 85 dB

Properties of Sound Waves (cont.) Frequency – the number of vibrations that occur per second Wavelength changes with frequency Measured in Hertz (Hz) 50Hz = 50 vibrations per second Which wave has the greatest frequency?

Properties of Sound Waves (cont.) Pitch – a description of how high or low the sound seems to a person High frequency = high pitch Low frequency = low pitch Example: a young girl might have a squeaky (high pitched) voice, an older man might have a deep (low pitched) voice

Quick Action – Sound Waves Write About Get with a partner and discuss the physical properties of sound waves: intensity, loudness, frequency and pitch. Write a phrase or sentence describing how frequency and pitch are related. Write another phrase or sentence describing how intensity and loudness are related.

Doppler Effect Sound Waves The apparent change in frequency as a wave source moves in relation to the listener Sounds moving toward a person – Waves are at a higher frequency, so pitch appears to increase (high) Sound moving away from a person – Waves are at a lower frequency, so pitch appears to decrease (low) https://goo.gl/Tv64hZ Chris, can you put this video clip on this slide?

Check for Understanding Can you… define sound? explain how sound waves travel? describe the physical properties of a medium and explain its effect on the wave‘s speed? compare the properties of waves that affect what we hear? demonstrate the Doppler effect? Clear up any confusion and answer questions.

Ear Broken into three sections: outer, middle, and inner

Outer Ear Only two structures Actual “ear” that we see is the pinna Opens to a tube called auditory cannal Both are designed to collect logitudinal compression and rarefaction waves

Middle Ear Contains three bones (smallest in the body) All three - malleus, incus, and stapes (hammer, anvil, and stirrup) transmit the vibrational waves to the oval window, a membrane connected to the inner ear Also in middle is a opening to the pharynx called the Eustachian tube Regulates pressure affecting tympanic membrane

Inner Ear Actual center where sound waves are processed Has fluid filled chambers called semicircular canals, responsible for spatial orientation The cochlea is the hearing centre Connected to auditory nerve, which relays info to auditory complex in cerebrum