Sound Ch

Review What’s a wave? What does it transport? Wave is a disturbance traveling through a medium transporting energy from one location to another. Remember the slinky? How is its wave similar to sound waves? Any guesses?

Listen... Listen, quietly, for a few minutes, writing down the name of each sound you hear, and where it is coming from Sound is the only thing that our ears can hear. The source of sound or any wave motion is a vibrating object

Quick Demo 1.Strike the prongs of a tuning fork with a pencil and then hold the fork close to your ear. What happens? Touch the prongs of the fork. What happens? 2.Strike the prongs of the tuning fork and place the ends of the prongs in a glass of water. What happens?

Objectives 1.Relate the pitch of sound to its frequency 2.Describe the movement of sound through air 3.Describe how bats and dolphins use sound 4.Compare the transmission of sound through air with that through solids, liquids, and a vacuum

Origin of Sound All sound produced by vibrating source –Strings on a guitar --> sound board (demo?) –Reed in a saxophone -->air column in sax

Quick Physiology Lesson Creating Sound: –Put your hand on your throat when you talk Windpipe blows air across your chords in your throat causing them to vibrate and make a sound Rubber band and cup demo Listening...

Determining Pitch Let’s review frequency. What is it? Frequency: # of vibrations per second Hz) Pitch of a note determined by frequency –High frequency --> high pitch

Wind instruments have a long, thin column of air Sound wave travels down tube, reflects off of the top and bottom, until it can escape Longer the tube, lower the f, lower the pitch Shorter the tube, higher the f, higher the pitch Opening/closing holes changes tube length which changes pitch Demo with recorder Pitch of Wind Instrument

Remember… Sound waves are mechanical waves –require a medium in order to transport their energy What’s the medium used to get this sound to your ears?

What pitches can we hear? 20 to 20,000 Hz Sound waves –below 20Hz Infrasonic –above 20,000Hz Ultrasonic

Elephants and Bats

Dolphins Send sound to the sea floor --> creates image Send sound to other dolphin --> put image in their head Receive and send info with the same “sense.” Do humans?

Checkpoint 1.The higher the frequency of a wave, the _________ the pitch. higher 2.Which chamber in a trumpet would produce a lower frequency: a short chamber or a long chamber? Why?  Longer chamber --> longer wavelength --> lower frequency

Compressed Air Vibrations produce pulses of compressed air, remember?remember? Do sound waves move like the slinky or the spring? (show both) What type of waves are sound waves? Longitudinal!

Compressions vs. Rarefactions These pulses push into their neighbors, who push their neighbors, etc. Compressions: –pulse of compressed air i.e., door/curtain Rarefaction: –a disturbance in air when pressure is lowered Candle Demo

Sound needs a medium

What are the best conductors of sound? Put these in order: liquid, air, solid. Why is one a better conductor than the other? –Depends on object’s elasticity--more on this next lecture Can you hear voices in outer space? Tin can activity