Sound Part One

World of Sound Everyday your world is filled with a multitude of sounds. Sounds help us communicate.

What is sound? Sound is a pressure disturbance that moves through a medium in the form of longitudinal waves. Waves of sound energy move outward in all directions from the source. When a force is exerted on an atom, it moves from its rest or equilibrium position and exerts a force on the adjacent particles. These adjacent particles are moved from their rest position and this continues throughout the medium. This transfer of energy from one particle to the next is how sound travels through a medium.

Sound or pressure waves are made up of compressions and rarefactions. Compression happens when particles are forced, or pressed, together. Rarefaction occurs when particles are given extra space and allowed to expand. One compression and one rarefaction is one wavelength.

Without a medium there are no particles to carry the sound waves. In places like space, where there is no atmosphere, there are too few particles to transfer the sound energy.

How we hear… Sound travels to your eardrum and causes your eardrum to vibrate. This vibrates the tiny bones in your ear the vibrations travel into the cochlea. there are hundreds of special cells attached to nerve fibers, which can transmit information to the brain.The brain processes the information from the ear and lets us distinguish between different types of sounds. Show: DSN What is Sound

Why are sounds different? As you know, there are many different sounds. Fire alarms are loud. Whispers are quiet. Sopranos sing high. Tubas play low. every one has different voices. The differences between sounds are caused by Intensity Loudness Pitch Frequency Tone

Intensity Intensity is the amount of energy a sound has over an area. Amplitude is a measure of energy. The more energy a wave has, the higher its amplitude. As amplitude increases, intensity also increases. As amplitude decreases, intensity also decreases. Larger amplitude = higher intensity = louder sound.

Loudness We are used to measuring the sounds we hear in loudness (volume). Loudness cannot be assigned a specific number, but intensity can. Intensity is measured in decibels (dB). Listening to loud sounds, sounds with intensities above 85 decibels, may damage your ears. 120 decibels is the threshold of pain.

Sounds and their Decibels Defense Siren…130 dB Rock Concert…110 dB Lawn Mower…100 dB Motorcycle…90 dB Vacuum Cleaner…70 dB Normal Conversation…60 dB Background Noise…40 dB Whisper…20 dB

Pitch Pitch helps us distinguish between low and high sounds. Pitch depends on the frequency. High pitches have high frequencies and Low pitches have low frequencies. Thunder has a frequency of only 50 Hertz, while a whistle can have a frequency of 1,000 Hertz. Show: What is Pitch

Tone Tone… or sound quality. When a source vibrates, it actually vibrates with many frequencies at the same time. Each of those frequencies produces a wave. Sound quality depends on the combination of different frequencies of sound waves.

Sound vs. Noise A sound must have an identifiable pitch, a good or pleasing quality of tone, and repeating pattern or rhythm to be music. A noise on the other hand has no identifiable pitch, no pleasing tone, and no steady rhythm.

Ultrasonic and Infrasonic waves The human ear is able to hear frequencies of 20 Hertz to 20,000 Hertz. Sounds that are too high for us to hear are called ultrasonic waves. Sounds that are too low for us to hear are called infrasonic waves. Show Hearing Test

Why do we see lightning before the thunder? The flash of light from lightning travels at about 300,000,000 m/s or 186,000 miles per second. Sound travels at about 0.2 miles per second. It takes sound nearly 5 seconds to travel 1 mile.

Sound and Speed Speeds of Sound in different mediums Rubber …60 m/s Air at 40 °C… 355 m/s Air at 20 °C …343 m/s Lead …1210 m/s Water …1482 m/s Glass …4540 m/s Copper …4600 m/s Aluminum… 6320 m/s Sound travels faster through materials that are more dense. The speed of sound through the air depends on the temperature. The speed of sound increase by 0.6 m/s with every increase of 1º C.