What is Sound– Definition– How is sound made?

Listening– How do we hear sound?

Advanced Listening– Sea Floor Drilling– Animals & Echo Location– Ultra-Sonic Medicine

Applications of Sound

A Definition of Sound

Sound waves are very special motions of molecules in the medium through which the wave moves. The medium can be air, water, or any other material.

Sound waves are special because the molecules in the medium travel in the same direction as the wave travels. Such waves are called longitudinal waves. Even though the wave itself travels very far and fast, the air molecules do not move very far or very fast as the sound wave passes through the air.

The study of sounds is called Acoustics

Spring animation by Tom Henderson

Vibrating things make sound!Stretch a rubber band and pluck it.What did you hear? How does the frequency of the sound change as therubber band gets tighter?

Sound travels through the air (gas),water (liquid) or brick (solid), as apressurized longitudinal wave. Cansound travel in a vacuum?

What is the difference between asound wave and a water wave?

How is sound made?

How do we Hear sound?

Physiology of the human ear Outer Ear Middle Ear-Eustachian Middle Ear-Ossicles Inner Ear

Physiology of the Human Ear

Ear physiology on web

Outer Ear

The auricle is the curved part of the ear attached to the side of the head by small ligaments and muscles. It consists largely of elastic cartilage, and its shape helps collect sound waves from the air.

The outer auditory canal is a tubular passageway lined with delicate hairs and small glands. The canal leads from the auricle to a thin taut membrane called the eardrum (tympanic membrane.)

"Ear," Microsoft® Encarta® Encyclopedia 99. © 1993-1998 Microsoft Corporation. All rights reserved.

Middle Ear:Eustachian tube

A narrow passageway called the eustachian tube connects the middle ear to the throat and the back of the nose. The eustachian tube helps keep the eardrum intact by equalizing the pressure between the middle and outer ear.

When ascending in an airplane the eardrums may cause pain as the air pressure in the middle ear becomes greater than the air pressure in the outer ear. When you yawn or swallow, the eustachian tube opens, and some of the air in the middle ear passes into the throat, adjusting the pressure in the middle ear to match the pressure in the outer ear. This equalizing of pressure on both sides of the eardrum prevents it from rupturing.

Microsoft® Encarta® Encyclopedia 99. © 1993-1998 Microsoft Corporation. All rights reserved.

Middle Ear-Ossicles

Inside the middle ear is a linked chain of three ossicles, or very small bones. They are called the malleus, or hammer; the incus, or anvil; and the stapes, or stirrup.

Vibrations of the eardrum move the hammer, which moves the anvil, which in turn moves the stirrup. As sound vibrations pass from the relatively large area of the eardrum through the chain of bones, which have a smaller area, their force is concentrated. This concentration amplifies the sound just before it passes through the oval window and into the inner ear.

Inner Ear The cochlea is a fluid-filled, coiled tube that

houses thousands of hair like projections that receive sound vibrations from the middle ear and send them on to the brain via the auditory nerve. In the brain they are recognized and interpreted as specific sounds.

The vestibule helps the body maintain balance and orientation by monitoring the sensations of movement and position.

The three semicircular canals. direct body balance when the body moves in a straight line or rotates in any direction.

"Ear," Microsoft® Encarta® Encyclopedia 99. © 1993-1998 Microsoft Corporation. All rights reserved.

Sea Floor Drilling

Deep-sea drilling rigs can extract material from more than 1500 m below the ocean floor. Acoustic positioning beacons are used to keep the rig in place. The beacons send sonar waves to the surface where hydrophones on the bottom of the ship receive them. A computer-pilot processes this information and uses the tunnel thrusters to compensate for drift and wind.

"Deep-Sea Drilling," Microsoft® Encarta® Encyclopedia 99. © 1993-1998 Microsoft Corporation. All rights reserved.

Bats and Echo Location

Bats use auditory stimuli to navigate and to locate and catch insect prey. High frequency pulses of sound emitted by the bat bounce off objects in its path and return as echoes.

Different types of sensory cells in the bat’s brain interpret these echoes to determine the location and some physical properties of the objects, creating a spatial "map" that governs the bat’s behavior. Curiously, the noctuid moth uses a similar but less sophisticated adaptation to detect and evade predatory bats in the night sky.

Dolphins…

Echolocation and Prey Detection," Microsoft® Encarta® Encyclopedia 99. © 1993-1998 Microsoft Corporation. All rights reserved.

Dolphins and Echo Location

– Dolphins live in a world of sound. They use sounds to communicate and each animal has its own signature whistle, like a name. They can hear sounds as high as 150 kilo Hz.

– Dolphins use sonar or “echo-location” to navigate and find their prey in dark and murky water. A series of "clicks" are made with the blow hole and emitted through their forehead. The echoes are heard through their jaw and enable the animal to form "sound images" of their surroundings.

Dolphins may even be able to use super strong bursts of clicks to stun fish, making them easier to catch.

Echolocation and Prey Detection," Microsoft® Encarta® Encyclopedia 99. © 1993-1998 Microsoft Corporation. All rights reserved.

Bats …

Ultra-Sonic Medicine

Ultrasound, or sound waves with frequencies above detection by the human ear, is commonly used in obstetrics to diagnose both the age and health of the developing fetus.

An ultrasound-emitting device called a transducer is placed against the skin of the pregnant woman’s abdomen. The sound waves reflect in varying degrees when they contact tissues of different density and elasticity. The pattern of echoes is detected by the transducer and is converted into a moving image seen on a monitor.

Microsoft® Encarta® Encyclopedia 99. © 1993-1998 Microsoft Corporation. All rights reserved.

Ultrasound is also used to detect tumors, damage, or abnormalities in the liver, kidney, ovaries, eyes, and other organs. High energy ultrasound can even break apart kidney stones!

Secret Hyper-Link

The Secret Word is…

Resonance