Hearing

How hearing works First, the ear gathers the compressional waves. Next, the ear amplifies the waves. In the ear, the amplified waves are converted to nerve impulses that travel to the brain. Finally, the brain decodes and interprets the nerve impulses.

I’m all ears Outer Ear -- where sound waves are gathered. Middle Ear -- where waves are amplified Inner Ear -- converts waves to nerve impulses

I’m all ears Eardrum -- a tough membrane about 0.1 mm thick Cochlea –spiral-shaped structure –Filled with liquid and tiny hairs –Convert waves to impulses

How does it sound? Amplitude → Intensity → Volume (Loudness) –Intensity is the amount of energy that flows through a wave Intensity decreases with distance –The sound covers more area –Some of the sound energy is converted to other forms Decibels –Adding decibels is the same as multiplying intensity –A 50 dB sound is ten times louder than a 40 dB sound

How does it sound? Frequency → Pitch → Note –Remember, frequency is a measure of how many waves pass by in a second –Pitch is how high or low a note sounds Octaves -- If you go “up” an octave, you double the frequency Ultrasonic and Infrasonic –Ultrasound → f > 20,000 Hz –Infrasound → f < 20 Hz

Doppler The Doppler Effect -- change in frequency due to a moving wave source –Ambulance –Ice Cream Truck –Race Car It also works for a moving observer and a stationary source

Doppler The Doppler Effect also works for electromagnetic waves –Doppler Radar –Radar Detection (police) –Used in astronomy to find if objects are moving towards or away from us