Sound

What causes Sound? All sounds have one thing in common…. They are all created by VIBRATIONS! A vibration is the complete back and forth motion of an object.

Sound Waves Sound waves are LONGITUDINAL waves caused by vibrations and carried through a substance. Sound travels in all directions away from the source. Sound carries energy; NOT MATTER!

Detecting Sound How do we hear sounds? Watch this video to find out! How Humans Hear!

Review Questions! longitudinal Sound waves carry energy, not matter! Sound travels as a _____________________ wave. Why wouldn’t a person at a rock concert feel gusts of wind coming from the speakers? What do you call the area where particles are squeezed together here? What do you call the area where particles are spread out? 5. Which part of the ear increases the size of the vibrations entering the ear? Sound waves carry energy, not matter! compressions rarefactions Middle ear

Properties of Sound!

Speed of Sound in Different Media The speed of a sound wave depends ONLY on the medium through which it is traveling. You would think that sound would travel faster through air, but that is not correct! Watch this! And this! As always, sound CANNOT travel in a vacuum. Sound is a mechanical wave that must have a medium! Speed of Sound in Different Media Medium Speed (m/s) Vacuum Air (20°C) 343 Water (20°C) 1,482 Steel (20°C) 5,200

Pitch and Frequency Reminder: Frequency is the number of waves per second. Frequency is measured in Hertz (Hz) How high or low a sound seems to be is called the pitch. High frequency sounds have a high pitch. Low frequency sounds have a low pitch. Check it out here!

Table 2 Frequencies Heard by Different Animals Frequency and Hearing Humans cannot hear all frequencies of sound. The chart below compares human hearing to that of other animals. Sounds that have a frequency too high for people to hear are called ultrasonic. Table 2 Frequencies Heard by Different Animals Animal Frequency range (Hz) Bat 2,000 to 110,000 Porpoise 75 to 150,000 Cat 45 to 64,000 Beluga whale 1,000 to 123,000 Elephant 16 to 12,000 Human 20 to 20,000 Dog 67 to 45,000

Loudness and Amplitude Loudness is a measure of how well a sound can be heard. Basically, how loud a sound is  Loudness is different from pitch. The amplitude of a sound wave determines how loud it is. The higher the amplitude, the louder the sound. If you hit a drum harder, you apply more energy and make the vibration larger. Therefore, the sound is louder! Watch here!

How loud is too loud? Table 3 Decibel Levels of Common Sounds Decibel level Sound the softest sounds you can hear 20 whisper 25 purring cat 60 normal conversation 80 lawn mower, vacuum cleaner, truck traffic 100 chain saw, snowmobile 115 sandblaster, loud rock concert, automobile horn 120 threshold of pain 140 jet engine 30 m away 200 rocket engine 50 m away Now you will do a Gizmo and find out more about pitch and loudness of sounds!

The Doppler Effect!

What is the Doppler Effect? The Doppler Effect is an apparent change in pitch of sounds made by moving objects. To get a better idea of what the Doppler Effect is, watch this! Label the areas of high pitch and low pitch on your picture in your notes. To see how we use the Doppler Effect, watch this! Low Pitch High Pitch