the nature of sound. objectives what is sound? what physical properties of a medium affect the speed...
TRANSCRIPT
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.
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.
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
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