SCIENCE OF SOUND

Sound is a Form of Energy

Sound is a Compressional Wave

Sound requires a medium

Hearing

Uses of Sound

Sound and Music

Sound is a form of Energy

Try this test. Put your index and middle finger on your neck. Say the word "Aah" as loud as you can. Then try it as soft as you can. You not only hear a sound, but you can feel a movement inside your throat. When you say, "Aah", your vocal cords vibrate. That means they move quickly back and forth. As your vocal cords vibrate they produce sound.

COMPRESSIONAL WAVES

Sound waves are compressional waves. Use a toy slinky. Stretch it out between two students. One student should grab several coils on the slinky. Then let go. You will see the group of coils go across to the other student. Then come back to the starting student. Make sure you notice how the coils stay together. This is what sound waves do.

SOUND REQUIRES A MEDIUM

A sound wave moves through matter, such as air, just like a wave moves through a slinky. We have drawn three pictures of a tuning fork to help you visualize how air molecules might look around a tuning fork.

SOUND REQUIRES A MEDIUM

When the tuning fork is at rest, the fork is surrounded by molecules in the air.

The molecules are arranged randomly.

Note that this is a gas, so molecules are far apart and not connected.

SOUND REQUIRES A MEDIUM

As a tuning fork's prongs move apart because of a vibration, the molecules ahead of it are crowded together. They look like they are being pushed together. They bump each other.

SOUND REQUIRES A MEDIUM

As a tuning fork's prongs come back together, it leaves a region that has fewer molecules than usual.

The region of a sound wave in which the molecules are crowded together is a compression. The region of a sound wave in which particles are spread apart is a rarefaction.

SOUND REQUIRES A MEDIUM

As a tuning fork vibrates, it causes molecules in the air to move. The molecules bump into other molecules nearby, causing them to move. This process continues from molecule to molecule. The result is a series of compressions and rarefactions that make up sound waves.

Unlike light waves, sound waves do not travel through a vacuum. They need matter to travel. That is why sound can travel through a wall.

What happens when we hear a sound?

An object like a violin vibrates the air, and those vibrations travel from the violin through the air until they reach us. But we don't hear a violin with our noses or our elbows! These vibrations need to travel into our ears for us to really hear them.

So what is so special about our ears that allows us to hear sound? Well, the ear is naturally designed to collect, focus, and transmit sounds through a tiny and efficient conveyance system called the auditory pathway.

Auditory Pathway

Sound vibrations from the outside world are conveyed through this system until they reach the brain, and we hear the sound.

Sound vibrations, or sound waves, are collected by the outer ear (those are the things hanging on the sides of your head!) and travel into the ear canal, where they bump up against the eardrum. The ear drum vibrates in sympathy with these sound waves. As it vibrates, it moves a series of tiny bones in the middle ear, which carry the vibrations to a fluid-filled tube called the cochlea in the inner ear. The fluid inside the cochlea vibrates a series of tiny hairs called cilia, which are attached to auditory nerves. The movement of these cilia stimulates the nerves, and they send signals to the brain, which, in turn, processes these signals into the sounds we hear.

The diagram on the right shows the outer ear and the ear canal. The outer ear is the part that is on the outside of your body. The outer ear catches the sound waves and funnels them into the middle ear through the ear canal.

The diagram on the right shows the middle ear. It is located in the ear canal. It is also called the "Tympanic Cavity".This is also referred to as the ear drum. The vibrations hit the ear drum. When you have a middle ear infection there is fluid in the middle ear that stops the ear drum from moving.

The diagram to the left shows the inner ear. It is in the inner ear that the sound vibrations are changed into energy that our brains can understand. The fluid inside the cochlea(This is the section that looks like a sea shell.) vibrates a series of tiny hairs called cilia, which are attached to auditory nerves. The movement of these cilia stimulates the nerves, and they send signals to the brain, which, in turn, processes these signals into the sounds we hear.

Uses of Sound

Echo's

Not all sound that hits matter is absorbed. Some of it is reflected. That means sound bounces off the solid matter the way a tennis ball bounces off a wall. Sound reflected back to its source is an echo.

SOUND INSULATION

Insulators Drapes

carpets

When sound strikes soft materials, much of the sound is absorbed. A sound insulator is a material that absorbs most of the energy of sound waves.

Sonar

Geologists use their knowledge of rocks to help them locate oil resevoirs. Earthquakes can be tracked and their waves understood once the geologist understands how the earthquake waves travel through different kinds of rocks and magma.

Ocean exploration

Earthquake vibrations and waves

Marine mammals and bats use sonar location

The military uses sonar in submarines and in planes

What Is Music?

– What is the difference between musical sound and noise?

– Noise results when irregular vibrations are made at irregular times. Musical sound results when regular vibrations of the voice or a musical instrument are produced.

– There are three main kinds of musical instruments:

– String instruments

– Wind Instruments

– Percussion Instruments

You can see a picture of a sound wave on the screen of a device called an oscilloscope.

REVIEWING WAVES

– Look at the diagram. The compressions, in which particles are crowded together, appear as upward curves in the line. The rarefactions, in which particles are spread apart, appear as downward curves in the line.

– Three characteristics are used to describe a sound wave. These are wavelength, frequency, and amplitude.

Wavelength; this is the distance from the crest of one wave to the crest of the next.

Frequency; this is the number of waves that pass a point in each second.

Amplitude; this is the measure of the amount of energy in a sound wave.

Pitch

This is how high or low a sound seems. A bird makes a high pitch. A lion makes a low pitch.

AMPLITUDE TELLS HOW LOUD THE SOUND IS.

– Sounds also are different in how loud and how soft they are.

– The more energy the sound wave has the louder the sound seems. The intensity of a sound is the amount of energy it has. You hear intensity as loudness.

– Remember the amplitude, or height of a sound wave is a measure of the amount of energy in the wave. so the greater the intensity of a sound, the greater the amplitude.

REGULAR PATTERNS SOUND NICE

A pleasant sound has a regular wave pattern. The pattern is repeated over and over.

The waves of noise are irregular. They do not have a repeated pattern.