Category: unit 4: Energy

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01/17 PotU: Sound, energy, and music

Warm up

Copy and complete the following sentence by selecting one of the bold words:

In musical instruments, low notes are created by making the string or tube longer or shorter, or by making it thicker or thinner.

Today’s videos

What is sound?

How does sound travel

Highlights from videos

What is sound

image of complex sound wave
image of a sound wave composed of many different waves combined
  • Compression: Areas where atoms/molecules are squeezed closer together (have more elastic energy).
  • Rarefaction: Areas where molecules are spread apart (have less elastic energy).
  • Hz (short for Hertz, like the rental car company) is a measure of the frequency: 1 cycle every second = 1 Hz. An example in sound: 440 Hz is the note “A.”
  • The medium is the substance the waves travel through. The medium moves only a short distance; it’s the energy that moves the entire distance from the source of the wave to whatever receives that energy (e.g. from a speaker to your ear).

How does sound travel

This video starts with a thought experiment. Thought experiments are experiments we can’t actually do, but by thinking about that situation, it helps us to understand. By looking at a super-long bar of metal, we can ‘slow down’ sound.

  • Wave motion can be thought of as a chain reaction of one portion moving the portion next to it.
  • Sound waves are particles bouncing into each other
  • Particles only travel a short distance
  • Speed of sound depends on the material the medium is made up of.
  • Sound waves are not objects, they are the movement of energy.
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01/16 PotU: Sound energy

Notes from today

Image of inner ear.
The cochlea contains the nerves that resonate at different sound frequencies (notes).
  • Metronome: A device that keeps the rhythm; aka the “beat”
  • The shorter something is, the faster it vibrates.
    • We had a demonstration of the vibrating bar from the fall final; the shorter the bar was, the faster it vibrated.
  • Both string and wind instruments depend on lengthening or shortening the material that the sound is produced by to create different notes.
    • In some cases, the string is thicker (lower notes) or thinner (lower notes).
  • Our ears have hearing nerves: The long ones detect low notes, and the short ones high notes.
    • As we get older, our short cells tend to die off more than our long ones, so kids and teenagers can often hear sounds that adults can’t
    • A dog whistle is similar: The frequency is so high that people can’t hear it, but dogs can.

Sound is the rhythmic motion of air particles. So, similar to thermal energy, it is a type of kinetic energy.

Humans are said to be able to hear from 20 to 20,000 Hz (cycles per second). Test your hearing range with the video below. (I can hear from about 60 to 13,000 Hz.)

When the ball hits the tuning fork:

  • Kinetic (ball moving towards tuning fork) moves from the ball into
  • Sound energy from the tuning fork.

The video below shows a tuning fork being lowered into a glass of water, shot with a very high speed cameras (about 50 times faster than most cell phone cameras, and even faster than the slow-mo option on phone cameras).

Sample instruments

In the instruments below, notice how the length and/or thickness changes to make a range of notes.

Piano

Image of strings in a grand piano
Notice the long, thick strings on the left side (top in this photo) for the lower notes, and the short, thinner strings on the right (bottom in this photo).
The longer strings are placed above the shorter ones for space efficiency.

Trombone

Navy band trombone setcion
Trombones have a section that can slide in and out to make the tube length longer or shorter.

Clarinet

Two clarinets
Clarinet players place their fingers over the wholes in the instrument to make the effective tube length shorter. The lowest note is will all wholes covered.
Flutes and recorders use a similar system.

Percussion instruments

Percussion instruments
Percussion instruments come in all shapes and sizes. The larger ones generally produce lower notes.

Ukulele

Soprano ukulele
The ukulele has two thick strings in the middle, and outside strings are thinner.