3. SOUND

KEY POINTS

1. 

What is sound.  

Sound is movement of air. When we hit an object, when we twang the string of a musical instrument, when our own vocal chords vibrate in our throat, ... we simply make the air move. This is what we call sound waves.  (REMEMBER: when we speak we do not create an object called voice that travels through the air).

This part of the process is not too special, maybe. What is very special is what happens in the ear and brain:

-The ear has the incredible ability to transform the movement of air into a very precise electric message. This electric message is sent to the brain. The brain transforms this electric message into what we call sound.

Don´t you think this is incredible?

Check these vids: one , two, three, four, five, and six

2.  

Can we see these micro air vibrations?

Not directly. The air is formed by molecules (a combination of two or more atoms) that are too tiny even for the best microscope. The size of the two atoms that form oxygen (O and O = O2) is amazingly small. But scientists have always developed mechanisms to see the invisible by investigating the visible effects they have on the world around. A common "trick" is to use water (visible) instead of air (invisible).

-We can feel vibrations in our throat by positioning our fingers on it when we speak.

-We can sing the very low pitched budhist mantra OOOOOOOMMMMMMMMM! and feel it all around. (They say it relaxes you, and it even might Enlighten you)

-Using a tuning fork you can

• Strike it on the table. Hold it in front of a bright light. Can you see the tips vibrate?
• Tape or glue a table-tennis ball to a thread. Hold it up in the air. Strike the tuning fork on the table and move it close to the ball, gently. What happens?
• Dip a vibrating tuning fork into a bowl of water. Now surf.  

Now, check these vids: One, Two, Three, Four (effects of sound on water), Five (friction creating waves), Six

 3.

Sound through other materials than air.

• Sound (air moving) travels through air. So what would happen in outer space? Remember, there is no air out there. I´m sure you have see Star Wars or any space film with spaceship explosions. Would be hear the blast (kaboom!!!!!)? 111, 222. The answer is ... "NO". No air, no sound. 
• Now put your head under the water. Somebody outside of the bath tub asks you a question, do you hear it? If you do, with your mouth under the water answer the question. Did they hear you?               The answer should be..."YES". Sound can travel through water (remember water, H2O, has oxygen in it). Check these vids: Whales. 
• Tell your parents to shout at you directly in the face. Then, go to a room that is on the other side of the wall where you are at, close all doors. Tell them to shout again. What is the difference?               Sound might travel under the doors, and what is more important for us, it can make the wall vibrate (depending on how thick it is and the material). The wall will make the air on your side vibrate creating sound. 
• In fact, sound (a vibration) travels better and faster through solids than through air. Tap a table and listen. Then put your ear on the table and tap again. What has happened? 
• Have you ever made a STRING TELEPHONE (and here). This experiment proves that sound can travel better through string than through air. 
• On the other side, some materials are very good at stopping (muffling) sound. Sometimes it is very important, very important to stop noise. Your health depends on it. Look here.  
• Here you have a good reading about protecting your hearing. Here 

MUFFLING SOUND EXPERIMENT

In order to create the best noise protection, scientists had to develop experiments in order to test the best material. You can do the same and prove to yourself you are a great experimental scientist.

1. You need an object that makes sound. A small radio is a good example. (No cats, please)

2. You need a box to put the sound making object into.

3. You need the different materials that you want to test.

4. As you probably won´t have a sound sensor you might have a mobile phone that records sound.

5  Introduce the sound making machine in the box . Close it. Now, use different materials to cover the box and make the sound disappear.

Do you  want 10 house-points? Do this experiment and write me a report of how you did it,  with a final conclusion displaying your results.

  4.

WAVES.

We have a machine that can detected how air moves (sound waves) and represents this information with a special kind of line graph: a continuous line that goes from left to right and that moves up and down. This machine is called an OSCILLATOR.

These pictures are representations of what an oscillator shows:  

This picture shows the vocabulary we use to describe waves. 

Here we have two waves that have some elements in common, and others that are different. Before you continue reading stop to look carefully at both diagrams. Find what is the same and what is different. STOP READING AND LOOK ......................................................................................................................................................................... Ok, have you found the differences and similarities?

Good.

-Both have the same AMPLITUDE so both have the same VOLUME. Volume is how loud a sound is. On your TV or MP3 you have a volume control, don´t you? Volume is measured in Decibels.

-Both have different WAVELENGTH, or FREQUENCIES (both names are used). If you count the peaks of both you will see that the first one has 3 peaks. The second has 11. So we say that the second wave has a shorter wavelength, or a higher frequency. Wavelength and  Frequency are measured in Hertz.

The WAVELENGTH, or FREQUENCY indicates the pitch on the sound ( the musical note: do-re-mi A-B-C).

Check this next picture:

So, higher amplitude means higher volume, that means air moves higher and lower.

So, higher frequency means higher pitch, that means air moves faster.

Compare these now: HERE. Measure the amplitude and the frequency (wavelength).

 5.

Changing Volume and Pitch.

How to make Volume higher?

• Hit the drum harder!
• Shout with more air from your lungs! 
• Get a bigger instrument! (think of a church bell)
• Bite a bigger animal! (an elephant is louder than a turtle)
• Use a noisier material (metal is louder than hair)
• Stretch the material! (a drum skin can be stretched using this)
• Amplify the sound!!! ( do you remember the tuning fork touching the table? or a machine i and ii)

How to change Pitch?

• In a piano play a different key. Higher pitch is to the right 
• With a flute or recorder, more fingers covering the holes means lower pitch
• In a harp, shorter strings means higher pitch
• In a pan flute, a shorter tube means higher pitch
• In a guitar a thinner string means a higher pitch. 
• How about the finger positions in the guitar? Investigate. This video might (or might not) help you. 
• How about music with water cups, wine glasses or bottles? Investigate. 

6

EXTRAS

GAMES

1. Gets an Earful
2. Changing Sound
3. Science of Sound Animations
4. Physics of Sound Module!
5. Sound Ruler
6. Pitch me a Curve
7. Sound (for engineers)
8. Questions! and more Questions!
9. Sarah Jane
10. Revision
11. The Sound Factory
12. Other Experiments. Bottle hit and blow, Glass Xylophone and part ii, The Guitar, Stereo Hanger, Straw Kazoo, Super Sounding Drums, Sound Sandwich, 
13.  

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Do you want to watch a 1933 documentary by the Encyclopaedia Britannica. Here

Some info about the the "magic" of certain frequencies: One, Two, Three.