The Physics Of Sound Why do we hear what we hear? (Turn on your speakers)

How are sound waves produced? Mechanical waves Sound energy requires matter in order to transport it Sound Energy (pulses) create vibrations causing changes in pressure

How are sound waves produced?produced A longitudinal wave caused by pressure fluctuations in vibrating objects: –Compressions: high pressure regions (crowded area) –Rarefactions: low pressure regions (relaxed area) –Frequency- # of compressions passing/second –Wavelength – distance between compressions –A 3-dimensional arrangement

What happens to the speed of sound in different types of matter (media)? Each substance transfers sound energy at a different rate The rate is dependent on: Tension - the higher the tension between molecules, the faster sound travels though a medium. thermal energy - higher the temperature, the faster the molecules move and allow sound to travel through medium.

How do you break the sound barrier? Supersonic - an object moves faster than the speed of soundSupersonic Moving at the speed of sound is known as Mach 1 Exceeding Mach 1 (the sound barrier) causes a shock wave known as a sonic boom Used to determine the speed of an aircraft What is meant by Mach 2, or 3 etc. ?

What is a sound detector? Converts sound energy into other forms of energy. Allows humans to observe a sound wave Often converts a compression (longitudinal wave) into a electromagnetic wave (transverse wave) –Ex. Microphone, the ear, ultrasonic machine

How does the ear work as a sound detector? collects and directs sound vibrates and send to the middle ear Lever system that amplifies sound vibrations Vibration of tiny hairs, transmitted to brain by nerves

The three components of sound are: Pitch (how high or low) Loudness (volume) Timbre (tone color)

What is the relationship between the frequency and pitch of a sound? Pitch is the highness or lowness of a sound perceived by humans –The qualitative observation (how high or low) –derived from the frequency Frequency is the measurable quantity –The quantitative observation –Measured in Hertz The higher the frequency, the higher the pitch

When the frequency of a sound doubles we say that the pitch goes up an octave. We can hear a range of pitches of about ten octaves. Many animals can make sounds and hear frequencies that are beyond what we can hear.

What frequencies can humans hear? Human Range (audible) 20 Hz - 20,000 Hz We hear best between 200 and 2000 Hz Changes with age and damage to the ear Ultrasonic –Anything above 20,000 Hz Used for sonar and medical diagnosis Infrasonic Anything below 20 Hz Heavy machinery, lightning, elephants We might not hear it, but you may feel these

What are the audible frequencies of other organisms? Grasshopper 100 to 50,000 Moth1000 hz – 240,000 hz Dog40 hz – 46,000 hz Cat 100 hz –60,000 hz Mouse1,000 hz – 91,000 hz Bull frog 100 hz – 3000 hz Tree frog 50 hz – 4000 hz Chicken 125 hz – 2,000 hz Elephant 16 hz – 12,000 hz Canary250 hz – 8,000 hz Beluga whale 1000 hz – 123,000 hz Tuna 50 hz – 1,100 hz Owl 20 hz – 12,000 hz Bat 2,000 hz – 110,000 hz Gerbil 100 hz – 60,000 hz Hippo 30 hz – 64,000 hz Ferret 16 hz – 44,000 hz

What is the relationship between the amplitude and loudness of a sound? Loudness is the volume a sound perceived by humans –A qualitative measure of the power in a wave –Can be quantified using “decibels” –derived from the amplitude Amplitude is the measurable quantity –The quantitative observation –Measured in meters The larger the amplitude, the more energy in a wave and the more powerful it is.

Loudness vs. Decibel Source of SoundDecibels Boeing Civil Defense Siren130 Jack Hammer120 Rock Concert110 Lawn Mower100 Motorcycle90 Garbage Disposal80 Vacuum Cleaner70 Normal Conversation60 Light Traffic50 Background Noise40 Whisper30 For every increase in 10 Decibels, the loudness DOUBLES!

Timbre Harmonic Content of sound Attack and Decay of sound Vibrato –Periodic changes in the frequency/amplitude

The of sound….

Diffraction of Sound

Refraction of Sound

Daytime refraction of sound due to ground temperature being higher than air

Nighttime refraction of sound when ground cools off quickly but warm air from the day stay in the air.