SOUND WAVES
Objectives: 1. WHAT IS SOUND? 2. HOW DO SOUND WAVES TRAVEL? 3. HOW DO PHYSICAL PROPERTIES OF A MEDIUM AFFECT THE SPEED OF SOUND WAVES? 4. WHAT PROPERTIES OF WAVES AFFECT WHAT WE HEAR? 5. WHAT IS THE DOPPLER EFFECT?
SOUND VIBRATIONS THAT TRAVEL THROUGH THE AIR OR OTHER MEDIA WHEN THESE VIBRATIONS REACH THE AIR NEAR YOUR EARS YOU HEAR THE SOUND.
HOW SOUND TRAVELS SOUND WAVES CARRY ENERGY THROUGH A MEDIUM (SOLID, LIQUID OR GAS) WITHOUT THE PARTICLES OF THE MEDIUM TRAVELING ALONG. Sound travels as a longitudinal wave.
HOW SOUNDS ARE MADE LONGITUDINAL WAVES ARE GENERATED WHEN A SOURCE OF ENERGY FORCES THE MATTER IN A MEDIUM TO VIBRATE. THIS BACK-AND-FORTH MOTION PUSHES AIR PARTICLES TOGETHER, GENERATING A COMPRESSION, OR MOVES THE PARTICLES APART, GENERATING A RAREFACTION. Compression Rarefaction
MEDIUM SOUND WAVES MUST HAVE A MEDIUM TO TRAVEL THROUGH. GAS AIR IS THE MOST COMMON LIQUID SOLID IN OUTER SPACE THERE ARE NO MOLECULES TO COMPRESS OR RAREFY, SO SOUND DOES NOT TRAVEL THROUGH OUTER SPACE.
SPEED OF SOUND DEPENDS ON THE PHYSICAL PROPERTIES OF THE MEDIUM IT TRAVELS THROUGH. ELASTICITY DENSITY TEMPERATURE AT ROOM TEMPERATURE, SOUND TRAVELS THROUGH AIR AT ABOUT 342M/S. Speed of Sound Medium Speed(m/s) Gases Air (0 o C) 330 Air (20 o C) 342 Liquids Fresh water 1,490 Salt water 1,530 Solids (25 o C) Hard wood 4,000 Glass 4,540 Steel 5,200
PHYSICAL PROPERTIES OF MEDIA ELASTICITY THE ABILITY OF A MATERIAL TO BOUNCE BACK AFTER BEING DISTURBED SOLID MATERIALS ARE USUALLY MORE ELASTIC THAN LIQUIDS OR GASES. PARTICLES OF A SOLID DO NOT MOVE VERY FAR, SO THEY BOUNCE BACK AND FORTH QUICKLY AS THE VIBRATION TRAVELS THROUGH THE OBJECT, WHICH ALLOWS WAVES TO MOVE FASTER. Distance traveled in 1 sec. Solid Liquid Gas
PHYSICAL PROPERTIES OF MEDIA (CONT.) DENSITY HOW MUCH MATTER THERE IS IN A GIVEN AMOUNT OF SPACE THE SPEED OF SOUND DEPENDS ON HOW CLOSE TOGETHER THE PARTICLES OF THE SUBSTANCE ARE IN THE MEDIUM. Gas Liquid Speed of Sound Medium Speed(m/s) Density Air 342 Fresh water 1,490 Solid Least dense Steel 5,200 Most dense
PHYSICAL PROPERTIES OF MEDIA (CONT.) TEMPERATURE - DEGREE OR INTENSITY OF HEAT PRESENT IN A SUBSTANCE OR OBJECT IN A GIVEN MEDIA (SOLID, LIQUID, GAS), SOUND TRAVELS MORE SLOWLY AT LOWER TEMPERATURES. Air Temperature ( o C) Speed (m/s) -20 318-10 324 0 330 10 336 20 342 30 348
PROPERTIES OF SOUND WAVES INTENSITY LOUDNESS FREQUENCY PITCH
PROPERTIES OF SOUND WAVES INTENSITY THE AMOUNT OF ENERGY THE WAVE CARRIES PER SECOND THROUGH A UNIT OF AREA AMPLITUDE INCREASES WITH INCREASED ENERGY MEASURED IN WATTS PER SQUARE METER (W/M 2 )
PROPERTIES OF SOUND WAVES (CONT.) LOUDNESS DESCRIBES WHAT YOU ACTUALLY HEAR. THOUGH NOT THE SAME AS LOUDNESS, THE GREATER THE INTENSITY OF A SOUND WAVE, THE LOUDER IT IS. MEASURED IN DECIBELS (DB) MAXIMUM SAFE LEVEL IS 85 DB
PROPERTIES OF SOUND WAVES (CONT.) FREQUENCY THE NUMBER OF VIBRATIONS THAT OCCUR PER SECOND WAVELENGTH CHANGES WITH FREQUENCY MEASURED IN HERTZ (HZ) 50HZ = 50 VIBRATIONS PER SECOND Which wave has the greatest frequency?
PROPERTIES OF SOUND WAVES (CONT.) PITCH A DESCRIPTION OF HOW HIGH OR LOW THE SOUND SEEMS TO A PERSON HIGH FREQUENCY = HIGH PITCH LOW FREQUENCY = LOW PITCH EXAMPLE: A YOUNG GIRL MIGHT HAVE A SQUEAKY (HIGH PITCHED) VOICE, AN OLDER MAN MIGHT HAVE A DEEP (LOW PITCHED) VOICE
DOPPLER EFFECT THE APPARENT CHANGE IN FREQUENCY AS A WAVE SOURCE MOVES IN RELATION TO THE LISTENER SOUNDS MOVING TOWARD A PERSON WAVES ARE AT A HIGHER FREQUENCY, SO PITCH APPEARS TO INCREASE (HIGH) SOUND MOVING AWAY FROM A PERSON WAVES ARE AT A LOWER FREQUENCY, SO PITCH APPEARS TO DECREASE (LOW) https://goo.gl/tv64hz