1. Sound! Speed of Sound: in air at 0°C, sound travels at 331.5 m/s (~760 mi/hr). When air is _____, the molecules move faster, and so sound travels more ______. When air is _____, the molecules move more slowly, so sound travels more ______. Sound travels 4 times faster in water and 10 times faster in steel than in air, b/c molecules in ______ and ______ are closer together. 1) How fast does sound travel when it is 40 ° C outside? 2) A baseball player hits a ball in 30 ° C weather. You hear the crack of the ball on the bat 0.5 seconds later. How far away is the batter? Sound Waves: are __________, __________ waves. We usually think of them as vibrations of the air that travel to our ears, but sound can travel in _______ and ______ too. (ex: dolphins, bass speakers.) Can sound travel in a vacuum, (which is an area with no molecules – no air, no nothing) like space? Why or why not? Doppler Effect: A __________ change in frequency when a sound source moves. Ex: Train whistle: when it is - coming toward you: seems higher pitched that reality going away from you: seems lower pitched than reality Hearing: Young, undamaged humans can hear frequencies between __ Hz (low pitch) and ______ Hz (high pitch). Below 20 Hz is called “______sonic” and above 20,000Hz is called “______sonic.” Bats squeak in ultrasonic range and listen to the echoes as sound waves bounce back off their surroundings. Elephants communicate with each other in infrasonic. Noise cancellation: (remember constructive and destructive interference) If 2 sound waves hit each other as compression + compression (“in phase”), it gets louder, but compression + rarefaction (“out of phase”) it gets quieter. Noise cancelling headphones have a computer chip listen to the noises you are hearing, and then tells a speaker in the headphones to make sound waves out of phase, so it cancels and you hear nothing! Natural resonance: musical instruments make use of natural resonance frequency – the pitch an objects naturally makes. Small objects vibrate faster, which is a higher pitch. (b/c they require less energy to vibrate) Large objects vibrate slower, which is a lower pitch. (more energy to vibrate) Ex: thick vs thin string on instruments, flute vs. trombone. Energy is carried by sound waves when molecules in the medium hit other molecules and knock them into the next molecules and so on, like a series of pool balls..

2. 3) The wavelength of a sound wave is 0.8 m and the frequency is 413.75 Hz. What is the speed of this wave? 1)Draw and label a transverse wave with 3 crests. Include amplitude, wavelength, crest trough and equilibrium point. 2)Draw a longitudinal wave using lots of dots. Label compression, rarefaction and wavelength. 4) The musical note of pitch A has a frequency of 440 Hz.What is the period of this pitch? At 0°C, what is the speed of this pitch in air? What is the wavelength of this pitch? 5) You stand 100 m from a sheer rock wall in the early morning, when the air temperature is 20°C. You shout “Physics!!!” at the wall. How long will it take the sound to travel to the wall and back as an echo?