Study Card Boxes: Box 1 Box 2 Box 3 Box 4 Box 5 Box 6 Box 7 Box 8 Box 9 Box 10
All learning is done through our senses. We see, we smell, we feel, we taste. We also hear! We hear all sorts of sounds. What causes sound? Sound is a form of energy produced by vibrations in matter. To vibrate means to move back and forth very rapidly. Think about a guitar string when it is plucked. A sound wave travels as a longitudinal wave through some type of medium. Sound travels through solids liquids and gasses only. Sound can not travel in a vacuum or through empty space. There can be no sound without vibration. Try experiment #1 to see exactly how sound travels through solid objects.
Materials
47 Dominoes
Masking Tape
Scissors
Meter-stick or Metric Ruler
Procedure
Cut two strips of tape, each 60cm long. Place the strips side by side on a table about 5 cm apart. Using the meter-stick, mark one tape with 4-cm spacings and mark the next tape with 2-cm spacings.
For trial 1, place the dominoes at each interval mark along the tape with 4-cm and 2-cm spacings.
At the same time, start both rows of dominoes falling by pushing over the first domino in each row. Observe which domino wave takes the shortest amount of time to reach each end. The shorter the time the faster the speed. Repeat this procedure two more times.
Things we learned:
Waves travel through a medium.
The dominoes represented a sound wave.
The different spacing of the dominoes represented different states of matter.
Have you ever heard a little kitty cat meow? How about a lion roar? These sounds each have a different pitch. Pitch is our perception of the frequency of a wave. How high or low a sound is, refers to pitch. The frequency of a wave is the number of waves that pass a certain point in one second. Frequency is measured in hertz. Humans can hear within a range of 20-20,000 hertz. Certain sound waves have a pitch so high we can not hear them. These sounds, which are above 20,000Hz, are called ultrasonic. Humans can produce sounds that fall in a range between 85-1,100Hz.
As sounds get closer to either audible end they need to be louder for us to be able to hear them. Loudness is the perception of the sounds intensity. Intensity is the actual measurement of the waves energy. The larger the compressions of the wave the more energy the wave carries. Intensity is measured using a unit called decibels-dB. Sounds over 90dB can start to cause some discomfort in you ears.
As we learned in the wave unit, reflection is the bouncing back of a wave. An example of a reflecting sound wave is an Echo. See the
wave notes for a diagram and the law of reflection.
The use of reflected sound waves is known as SONAR, Sound Navigation And Ranging. Ships will send out sound waves into the water. People would time to see how long before the sound would return to the ship. They would be able to calculate the distance of an object by using the speed of sound in water and the time in which the sound to return to the ship.
Try to think of a dog sleeping underneath a deck in the summer time. You call your dog and with in a second your dog comes running. How did your calls get from you to your dog?
What about when you are waiting for the ice cream man to come deliver some frozen goodies? You can hear the sounds of the truck but you cannot see the truck anywhere. The sounds from the ice cream truck and the calls to your dog reach their destination by diffraction. Sound waves diffract when they go around a barrier.
Have you ever swam underwater and heard people calling to you? How about sitting in your room with the door closed, and still being able to hear what is going on. These are examples of refraction. Sound waves refract when they travel from one medium into another. When sound waves refract they change speed and direction as they move into a new medium.
Two or more waves coming in contact with one another is called interference. There are two type of interference: constructive and destructive. Constructive interference produces a wave with a larger amplitude. Destructive interference produces a wave with a smaller amplitude. Wave interference can be easily heard. Do you know why D.J.’s take so much time when the set up their speakers? They are trying to get the waves to interfere with each other just right. If the waves combine in the wrong way all you will hear are jumbled sounds, which sound more like noise than music.
What is music anyway? Many people have their own ideas. Some people like opera, jazz, country, rock, rap or hip hop. Music is a matter of taste. Music is a combination of sounds pleasing to the ear. Every one finds different types of music pleasing.
Conversely, noise is a combination of sounds that are not pleasing to the ear. Do you find the sound of car alarms music to your ears? How about a baby’s cries of hunger? An excess of these unpleasant, unwanted sounds is considered noise pollution.
