ESCI 215 Chapter 8

Discovering Sound Waves 500 BC a Greek philosopher Pythagoras Length of strings of musical instruments affects the quality of sound 350 BC Greek and Roman philosophers a wave is a vibration that travels long distances 1500 AD Italian mathematician, Galileo Galilei, pitch is related to the frequency of wave vibrations 1800s North Americans herds of buffalo or wagons were heard by putting an ear against a solid object (rock or ground) to feel the vibration Today Railroad workers hold their ear to the track to listen for a train coming before doing repairs Mechanics listen for grinding bearings by holding a stick to the engine and their ear to the other end

What Sound Travel needs.. Sound needs some kind of matter to travel through solids, liquids and gases It cannot travel through a vacuum (i.e. space) because there is no matter Sound is easier to hear through solids than through air because of vibrations caused by sound waves

What is Sound? Energy caused by the vibration of matter Vibration = to move back and forth quickly Event 8-A and Even 8-B Is human voice produced by vibrations? Hold your hand to your throat when you talk and see

How Does Sound Travel? From one place to another using Longitudinal waves Longitudinal Waves Push-pull motion that moves sound along Transverse Waves are another type of wave ( not used in sound ) Side -to-side or up-and-down motion (like water) Event 8-D shows both types of waves Through Air Event 8-H shows how sound waves traveling through air can make salt dance Sound energy weakens quickly as it moves through air, unless the air is trapped in a tube (Event 8-I) Ships have “speaking tubes” to use when the phones do not work

How Does Sound Travel? Through Solids Events 8-F and 8-G show how sounds travels through solids using string Through Liquids Note: choose your demonstration carefully so that the sounds heard are from the water and not travelling through your body or the air (Event 8-J #1) Event 8-K shows how sounds travel through water What sounds have you heard underwater in the bathtub or while swimming?

The Speed of Sound Through Air: 330 meters per O°C Increases a little with increased temperature Decreases a little with decreased temperature Events 8-L and 8-M show that sound takes time to travel and this time can be measured Through other Materials: Sound travels faster in more elastic materials Elasticity is the ability of something to regain its original shape 1450 meters per second in water 4800 meters per second in steel Sound travels slower in denser materials (i.e. Concrete is very dense and absorbs sound) Density is the amount of the material in a specific amount of space If a material is dense but very elastic(i.e. steel) it will conduct sound well

Volume (Loudness) Volume is measure in decibels Volume of sound is affected by: Energy - energy = volume Distance - distance by 2 times = ¼ volume Surface Area - surface area = volume Resonance - the easier something can vibrate, the louder the sound Composition – what the object is made of affects how much it absorbs or conducts sound

Volume Cont’d Forced Vibrations By forcing an object to vibrate, sound volume increases Radio and TV speakers are forced to vibrate in time with incoming energy Events 8-O, 8-P and 8-Q demonstrate forced vibrations Natural Vibrations: Resonance Frequency is the # of vibrations per second Natural Frequency is the frequency that an object vibrates best at The object is “resonating” when vibrating at this frequency The volume is much louder Sing a loud tune into a piano; the piano strings that vibrate at that frequency will reply back

Volume Cont’d Event 8-S demonstrates how volume is increased when the natural frequency of an object is reached Event 8-T demonstrates how when an object reaches the natural frequency and resonates, the effect is increased Have you ever tried to swing against the natural frequency of a swing? What happens? What happens you swing with the natural frequency? Event 8-U demonstrates how distance affects the volume of sound (inverse square rule) distance by 2 times = ¼ volume

Pitch Pitch - how the frequency of sound affects our ears (highness or lowness) frequency = pitch It is different than volume Tuba is a musical instrument that has a low pitch and high volume Flute is a musical instrument that has a high pitch and low volume Generally, the bigger the object, the lower the pitch Not all frequencies can be heard by the human ear only frequencies of 20 – 20,000 vibrations per second Conversations are usually 500 – 3000 vps

Pitch Cont’d Pitch of an object depends on many factors Pitch for stringed instruments it depends on: Length longer lengths = lower pitch Diameter (thickness) larger diameter = lower pitch Tension (tightness) higher tension = higher pitch Event 8-V demonstrates these factors, but it also shows the importance of controlling variables Event 8-W demonstrates how to test 1variable at a time

Pitch Cont’d Pitch for other objects The more there is of something, the lower the sound The less there is of something, the higher the sound Event 8-X demonstrates this principle The empty bottle has more air inside, so the pitch is lower when you blow on the opening The half full bottle has less air inside, so the pitch is higher Have you noticed that when you saw something slowly the pitch is lower than when you saw it quickly? Why? How can you produce different pitched sounds from a ruler?

Music Musical tone is any sound made by regular vibrations of matter Musical composition has: Melody (tune) – the effect of single notes in sequence Rhythm – a timing pattern Harmony – the pleasing effect of 2 or more sounds together Using math we can determine which notes fit together best for harmony A note with a frequency of 100 vps is pleasing with a note of 200 or 300 vps A ratio of 1:2 or 1:3

Musical Instruments Classified into 3 groups: Percussion Produce sound when hit String Produce sound when plucked or bowed Wind Produce sound when blown (vibrates air columns) Divided into 3 more groups Flute Brass horn Reeds

Musical Quality Quality – how much a piece of music is pleasing to the ear Mouth, teeth, lips, tongue, and nose affect the quality Say: “Spring is in the air” Now say it with your nose plugged How is the quality affected? Say the alphabet with your mouth closed, then open, then without your tongue touching your teeth. What do you notice?

Assessment and Instruction Task: Have students make an instrument and write a paragraph for each of the following: How the instrument is classified and why What part of the instrument increases the volume and explain how What part of the instrument affects the pitch and explain how Evaluation: How well does it sound? Can it play several notes? Neatness, durability of model and writing Quality of writing and amount of logic used to answer questions

Discussion Where does this topic fit into the Science curriculum? Which grades and strands? Which curriculum objectives relate to the discrepant events?