Sound – a longitudinal wave phenomena that consists of successive compressions and rarefactions of the medium through which it travels.All sounds are waves produced by the vibrations of material objects. Sound waves must have a medium in which to travel.

What’s wrong with this?Suppose you're watching a science fiction movie

and one of the scenes involves a spaceship battle in outer space. Spaceship A launches a successful strike on spaceship B. The scene is presented from the perspective of spaceship A. The occupants of spaceship A view spaceship B blowing up as the result of the successful missile strike. They see the flames of the explosion and shortly thereafter hear the thunderous sound of the explosion. While the scene is definitely exciting, there is a significant fault with it in terms of the physics. What law/concept of physics was violated in the filming of the scene? Explain.

because: SOUND TRAVELS THROUGH A MEDIUM

The sound produced by the bell cannot be heard since it cannot travel through a vacuum.

SOUND IS A MECHANICAL WAVE

The compressions are regions of high air pressure while the rarefactions are regions of low air pressure.

The wavelength is commonly measured as the distance from one compression to the next adjacent compression or the distance from one rarefaction to the next adjacent rarefaction.

Correspondence between the longitudinal nature of a

sound

The speed of sound dependson the type of medium andthe temperature of the medium.

Waves encountering a surfaceWill all these raysbe reflected back to the person?

Can the blue person hearthe echo?

Reflection

SpecularReflection

DiffuseReflection

How can the two people hear each other?

Each of the rays traveled different lengths of way

Each of the rays used a different amount of time

Variable speed of soundCool air = low speed

Warm air = high speed

Wave front

Plane waves at constant speed

Rays are bent away From surface!

Refraction

Wave fronts if the air is warmer at the ground

Variable speed of sound

Cool air = low speed

Warm air = high speed

inversion

Rays are bent toward surface!

Wave fronts if the air is cooler at the ground

Refraction

Variable speed of soundwind

sound

Resulting motionof sound waves

Resulting motionof sound waves

sound

wind

The rays are bent upward upwind of

the source.

The rays are bent downward downwind of

the source.

Refraction

Reflection and refractionReflection:

At solid obstacles, a sharp change of direction Echo, ringing effect in halls

Refraction:Inhomogeneous speed, gradual change of

directionAir layers with different temperatures, wind

Reflection is of more importance to us than refraction.

Why can we hear around a corner?

Reflection ?

Sound waves at obstaclesTop view:

Diffraction

Diffraction at small openingSmall: d<<λWavelength large compared to opening

Shadow zone

Shadow zone

Diffraction bends the wave fronts heavily at the edges of a smallObstacle.

Diffraction at large openingSmall: d>>λWavelength small compared to opening

Shadow zone

Shadow zone

Diffraction bends the wave fronts only lightly at the edges of a largeobstacle.

The time it takes for sounds to reach you does not depend on how loud or high the sound is.

The speed of sound depends only on the medium through which the sound is traveling

Medium Speed m/s)

Air 343

Helium 1,005

Water 1,482

Sea Water 1,522

Wood (oak) 3,850

Glass 4,540

Steel 5,200

Speed of Sound in Different Media at 20

degrees Celsius

Try to solve:Speed at 20ͦ C

Speed at 0ͦ C

Speed at 33ͦ C

Air 343 m/s

Water 1482 m/s

Glass 4540 m/s

SOUND IS…In the physical sense,

1. The source of sound

3. An ear to receive the sound.

the disturbance in matter which are above, below and within the range of human hearing.

there are three requirements for sound. They are…

2. Medium for transmitting sound

In the physiological sense,

Group Activity:Each group will be asked to design a roof of

an outer pavilion (performance stage).. Apply the concept of properties of sound. How will you design?

Draw the side view only, and explain in class

Speed at 20ͦ C

Speed at 0ͦ C

Speed at 33ͦ C

Air 344 m/s 331 351

Water 1482 m/s 1470 1490

Glass 4540 m/s 4528 4548