Sound Sound is a longitudinal wave Sound like all waves is generated by something vibrating What is its medium?

Sound Without a medium, there is no sound

Sound Sound waves behave as all mechanical waves do Human ears are capable of hearing 20-20,000Hz roughly All sorts of things can create sound

How the Human Ear Works

Sound You loose your hearing as you age, it’s called presbycusis, what? I can’t here you! Speak up! You can also damage your ears by being exposed to loud sounds. Whenever you have “ringing” in your ears, you have sustained permanent hearing loss!

I Can’t Hear You Animals hear things differently than us!

How big is a sound wave? Sound travels at roughly 346 m/s (761 mph) in air We can hear frequencies between 20-20,000Hz (this is a generally accepted value) How long are the longest and shortest wavelengths we can hear? Do the math! Longest 17.3 meters Shortest =1.7cm

Directional Hearing Humans can tell what way a sound came from by the difference in time between when it gets from one ear to the next We can’t tell if a sound is directly in front or directly in back of us (with no reflection) We also can’t tell were a sound is coming from if the frequency is much longer than the distance between our ears That’s why subwoofers don’t need to be placed where the sound is coming from

Constructive and destructive interference Interference applet When setting up a sound stage, engineers have to worry about “dead spots” where the sound is destructive interference is taking place

Beats Beats-Periodic variation in the amplitude of a wave that is due to the destructive interference due to multiple sources with slightly different frequencies. Beats applet (visual) in phase/out of phase Second applet

Resonance Natural frequency-frequency at which something naturally vibrates Resonance- The effect of when a vibrating object forces another object with the same natural frequency to vibrate Tacoma Narrow bridge

Doppler Effect Doppler Effect- observed change in frequency when an there is relative motion between the source of sound and the observer Applet 1 Applet 2 Doppler Rocket

Sound barrier When an object exceeds the speed of sound for that medium, it creates a sonic boom The sonic boom happens anytime an object goes faster than the speed of sound. Applet 1

Decibel Scale Decibels (dB)- A measure of the Intensity of a sound wave, not necessarily the perceived loudness. Decibel scale is an exponential scale Each 10 decibels makes the noise 10 times loud. For example, a 80 dB sound it 1000 times as intense as a 50 dB sound