IPC12/05/03B day We will start today with a QUIZ over Chapter 12… …ya know, all that wave stuff! Look over your Ch 12 Vocabulary!

IPC12/05/03B day A Point to Ponder… –If a tree falls in the middle of the forest with no one around to hear the crash, does it make a sound?

IPC12/05/03B day Today’s Agenda: –Chapter 13 Notes on Sound –Some Sound Demonstrations –Secrets of Sound Video & Quiz

Chapter 13 SOUND

What is Sound? Sound is a pressure wave. The back and forth motion of the speaker creates alternating layers of high and low pressure. The pressure waves travel away from the speakers as sound.

Sound waves are longitudinal or compression waves because the air is compressed in the same direction the wave is traveling.

For most sounds, the amplitude of the pressure wave is very small, so it is hard to actually feel the pressure. But, you can feel sound at lower frequencies, if the amplitude is large enough. Examples: Sub-woofer, loud bass guitar If Sound is made of pressure waves, can we feel Sound?

Sound cannot travel in space! Sound requires a medium to carry it.

How do we measure the Loudness of Sound? It’s measured in decibels (dB) which is related to amplitude.

Anybody in the choir? How do we refer to the Frequency of Sound? We hear the different frequencies of sound as having different pitch. A low frequency sound has a low pitch. A high frequency sound has a high pitch.

High frequency sounds seem louder than low frequency sounds. This is because our ears are more sensitive to sounds between 100Hz and 2,000Hz. Humans can hear from ~20Hz to 20,000Hz. Which seems louder, High pitch or Low pitch?

Real Life Connections…. Adults: usually cannot hear above 15,000 Hz Children: can often hear up to 20,000 Hz We lose HIGH frequency hearing with age Loud sounds for extended time can cause the tiny hairs in the inner ear to weaken or even break off! (Musicians use earplugs when they play!!)

More Real Life Connections…. Ultrasound: 100,000 Hz… cannot hear this sound, but they pass through our bodies to make images (due to refraction and reflection) Used to find cracks in metal such as wings of planes

Have you ever heard of WHITE NOISE? More Real Life Connections….

WHITE NOISE contains an equal mixture of all frequencies. Because all frequencies are at the same level there is no pattern the brain can recognize. This lack of pattern is helpful for relaxing because it can drown out more distracting noises. More Real Life Connections….

What is the Speed of Sound? Sound is fast! The speed of sound is 343 m/s. That is the same as 660 mph. In comparison, ordinary passenger jets fly ~ mph.

What is Supersonic? Supersonic means traveling faster than the speed of sound.

Soundproofing More Real Life Connections….

How can Interference affect Sound Quality? Two waves can interfere to make the sound louder or softer. Destructive interference can cause Dead Spots in concert halls in areas where some of the sound cancels itself out. What could produce very loud spots?

Review This is what everyone needs to write down!

Review 1. While the range of human hearing is about 20 Hz to 20,000 Hz, humans hear best in the range from 100 to 2000 Hz

Review 2. Ultrasound is VERY high frequency sound that we cannot hear that is used to make internal images of materials, including the human body!

Review 3. White noise is sound containing an equal mixture of ALL frequencies of sound that can be soothing to listen to.

Review 4. Dead spots sometimes occur in a concert hall because destructive interference causes some of the sound to cancel out with its own reflections.

Review 5. The word supersonic describes motion that is traveling faster than the speed of sound.

Review 6. The decibel is a unit used to measure the loudness of sound.

Review 7. Standing Wave – a wave where both ends of the wave are fixed. - Nodes are points where the string doesn’t move. - Antinodes are points of the greatest amplitude.

Secrets of Sound Video Time!

Waves that “in phase” produce constructive interference and make loud sound Waves that are “out of phase” produce destructive interference and make soft sound