The Science of Sound Waves

Michelle Bertkeby:  Michelle Bertke

Sound can be a difficult concept to portray because the sound waves cannot be seen or touched.  Luckily, there are several at home experiments that demonstrate the properties of sound waves.

Water tank to show ‘Sound Waves’

Sound WavesYou can use a fish tank half filled with water to give a visual demonstration of ‘sound waves’.  Water is a perfect medium to show the propagation of waves. This demonstrates how sound waves travel though the air.  There are two ways to display this activity.  One way is to simply press your hands onto the top of the water and allow the waves to be made by the pressure of your hand.  This allows students to see how waves travel though a medium.  You can also use this to point out the aspects of a wave such as frequency and amplitude.  Another way to show waves is to place a speaker next to the tank and allow the sound to produce the waves.  This can show that sound is a form of pressure just like your hand. Read the rest of this entry »

Pocket Sound Blaster

Norman Barstowby: Norman Barstow

Frequency, Wavelength and Pitch:

Sound is a tone you hear as the result of regular, evenly spaced waves of air molecules. The most noticeable difference is that some tones sound higher or lower than others. These differences are caused by variations in spacing between the waves; the closer the waves are, the higher the tone sounds. The spacing of the waves – the distance from the high point of one wave to high point of the next one – is the wavelength.

All sound waves travel at about the same speed in a given medium. So, waves with a longer wavelength don’t arrive (at your ear, for example) as often (frequently) as the shorter waves. This aspect of a sound – how often a wave peak goes by – is called frequency by scientists and engineers.

The word that musicians use for frequency is pitch. The shorter the wavelength is, the higher the frequency, and subsequently the higher the pitch of the sound. In other words, short waves sound high; long waves sound low.

The Pocket Sound Blaster

Many instruments produce sound by vibrating a column of air inside a tube, e.g. flute, trumpet, and saxophone.   A sound wave is created by a vibrating object. The actual frequency at which an object will vibrate is determined by a variety of factors including the object’s size, the material the object is made from, and the medium in which the sound wave is vibrating.

Since frequency = speed/wavelength, an alteration in either speed or wavelength will result in an alteration of the natural frequency.

When you blow into the side hole of the Pocket Sound Blaster, (SNG-600) the Pocket Sound Blasterrubber diaphragm vibrates as air pressure repeatedly increases and then is released.  The vibration then resonates through the chamber and exits through the Pocket Sound Blasteropen end of the tube.

Activity #1:

As you blow into the hole of the Sound Blaster, lightly touch the diaphragm to see whether the sound changes.  Does the pitch get higher or lower? Drummers can change the tension on their drum-heads to change the pitch.

Activity # 2:  Slide Trombone

As you blow into the hole of the Sound Blaster, insert your other hand’s thumb and move it in and out. Notice any change in pitch?  For longer tubes, use a cork on the end of a barbecue skewer or thin wooden dowel to change the column of air and to make your own ‘trombone’.

Activity #3: Length of the tube (column of air)Pocket Sound Blaster

Use cardboard tubes (toilet paper, paper towels, mailing tubes) of varying lengths to make the Pocket Sound Blaster tube longer. You’ll have to taper the ends of the cardboard tubes to make them fit the outside diameter of the Pocket Sound Blaster.

Pocket Sound BlasterShorter is Higher — Longer is Lower:   Change the length of this vibrating column of air by varying the length of a tube.  Because the Pocket Sound Blaster is short, it produces a higher pitch or frequency.  This happens because sound waves can travel, or vibrate, a shorter distance faster than a longer distance.

Activity # 4:

Since the Pocket Sound Blaster tube is approximately 3″ long, make a series of card board tubes in 3 inch increments (3”, 6”, 9”, 12” etc.) to see how this affects the tone.

Activity #5:

The diaphragm of the Pocket Sound Blaster is held on by the plastic ring. Gently Pocket Sound Blasterremove the ring and explore with other diaphragm material:  wax paper, parchment paper, zip bag plastic, other balloons, latex or Nitrile glove material, etc. What changes do you discover?

Activity #6: Sound Energy

Can the sound from the Pocket Sound Blaster perform work?

  1. Try to blow out a birthday candle with the Pocket Sound Blaster.
  2. Put some confetti or puffed rice cereal in the tube and blow through the side hole. What happens?
  3. Hold the Sound Blaster so the rubber end is upright.  Place some puffed rice on the latex and blow.  Observe the movement of the puffed rice due to the vibration of the surface.