What is Sound?
Sound is a vibration, or wave, that travels through matter (solid, liquid, or gas) and can be heard.
The following information comes from Ducksters: Basics of Sound and Ducksters: Pitch and Acoustics.
How does sound move or propagate?
The vibration is started by some mechanical movement, such as someone plucking a guitar string or knocking on a door. This causes a vibration on the molecules next to the mechanical event (i.e. where your hand hit the door when knocking). When these molecules vibrate, they in turn cause the molecules around them to vibrate. The vibration will spread from molecule to molecule causing the sound to travel. Sound must travel through matter because it needs the vibration of molecules to propagate. The matter that transports the sound is called the medium.
Speed of Sound
The speed of sound is how fast the wave or vibrations pass through the medium or matter. The type of matter has a large impact on the speed at which the sound will travel. For example, sound travels faster in water than air. Sound travels even faster in steel. In dry air, sound travels at 343 meters per second (768 mph). At this rate sound will travel one mile in around five seconds. Sound travels 4 times faster in water (1,482 meters per second) and around 13 times faster through steel (4,512 meters per second).
The volume of sound is the measure of loudness. To quantify volume we use decibels. The more decibels, the louder the sound is. A soft sound, like a whisper, will measure around 15-20 decibels. A loud sound like a jet engine is more like 150 decibels. The threshold of pain occurs at around 130 decibels. Loud sound can actually damage your ears and cause loss of hearing. Even sounds as loud as 85 decibels can ruin your ears if you listen to them over a long period of time. For this reason, it’s a good idea to not listen to loud music or have your headphones turned up too loud.
Pitch and Frequency
An important measurement of sound is the frequency. This is how fast the sound wave is oscillating. This is different than how fast the wave travels through the medium. Frequency is measured in hertz. The faster the sound wave oscillates the higher pitch it will have. For example, on a guitar a big heavy string will vibrate slowly and create a low sound or pitch. A thinner lighter string will vibrate faster and create a high sound or pitch.
In our STEM Club session on January 6th we’ll be learning even more about sound and make our own Membranophones!
If you would like to participate you will need the following materials:
- Clean, empty plastic water bottle, any size (bottles with ridges work best)
- Scissors (for children) or utility knife (for adults only)
- Latex, rubber, or vinyl glove (or a balloon, although it’s harder to work with)
- Rubber band
- Hole punch
- Drinking straw
- Sheet of construction paper (card stock works too)