The Nature of Sound

Objectives What is sound? What physical properties of a medium affect the speed at which sound travels through it?

What is a Sound Wave? Sound waves carry energy through a medium without the particles of the medium traveling along.

What is the medium through which sound waves travel?

What is a Sound? Sound is a disturbance that travels through a medium as a longitudinal wave.

How are sound waves made? Air is made up of tiny particles Vibrations generate a disturbance in the molecules in the air The force of the disturbance pushes the molecules closer together generating a compression In between vibrations, the molecules spread out and rarefactions are created.

Sound Waves

Pluck a guitar string………. Plucking the string causes vibrations The vibrations cause compressions and rarefactions The sound wave travels through the air in longitudinal wave form

SING! Vocal cords are like a guitar string When you speak, air is forced past your lungs and rushes past your voice box Larynx 2 folds of tissue vibrate creating sounds

Let’s try it!

How else can sound travel? Sounds can travel through solids and liquids Knock This causes vibrations in the medium The vibrations generate sound waves

How far can the vibrations travel? You can put your ear on a train track and hear the train coming from miles away. Why?

Limitations of Sound: Sounds can travel only if there is a medium through which to transmit the compressions and rarefactions

Sound in Space Sounds can not travel through outer space No molecules in space to compress or rarefy There is no matter in space

How does sound bend? Diffraction – sound waves can bend and spread around a corner Sound waves bend out (diffract) and spread when they hit a barrier or a hole in a barrier

The speed of sound in different media: The speed of sound depends on the physical properties of the medium it travels through. Air at room temperature – 342 m/s The speed sound can travel through a medium depends on: –Elasticity –Density –Temperature

Elasticity – the ability of a material to bounce back after being disturbed Speed depends on how well the particles in the medium bounce back after being disturbed The more elastic, the faster sound travels Examples: –Solids are more elastic than liquids –Gases are not very elastic at all

Density Density – how much matter, or mass, there is in a given amount of space or volume The speed of sound depends on how close together the particles of the substance are.

Density Continued Sound travels more slowly in denser mediums More dense means more mass per volume The particles of a dense material do not move as quickly as those of a less dense material

Temperature Sound travels more slowly at lower temperatures than at higher temperatures At low temperatures, the particles of a medium are sluggish Sound waves move and return to their original positions more slowly than they would at high temperatures.