1Midterm exam: Tuesday, Oct. 5Location: Ramaley Biology (due east of Norlin Library), room C250.Time: 7-8:30 PM. Format: Multiple choice, a couple of essays.You can bring: * a 3X5 index card with handwritten information* a calculator* a number 2 pencilYou cannot have: and open text bookList of topics available online Special office hoursMegan O’Sadnick, 12-1:30 MondayIn the Help RoomUpdatesThis week and next: Homework #6 due Saturday noon Today: Sound Next Tuesday will be review for exam.Everyday Life Experience at the BallparkYou are at Coors Field sitting in the bleachers in the outfield (~325 ft from the batter). You see the bat hit the ball. About how long will it take before you hear the bat hit the ball? a. About 10 secondsb. About 2 secondsc. About 0.3 secondsd. About 0.03 secondse. There will be no delay between seeing ball hit and hearing ball hit.Question: You are at Coors Field sitting in the bleachers in the outfield (~325 ft from the batter). You see the bat hit the ball. About how long will it take before you hear the bat hit the ball?c. About 0.3 secondsSpeed of Sound in Air = 331 m/s at 0 degree C343 m/s at 20 degree C(Speed of Light = 3 X 108 m/s… much, much faster)About 0.3 second means ~ 325 ft away from batter.In 0.03 seconds, sound travels ~ 32 ft and in 2 sec, ~2,160 ftHow fast is that sound traveling? Speed = distance/time = 325 ft/0.3 s = 1083 ft/s or 330 m/s What causes the delay between seeing and hearing? A sound wave travels or propagates through the air and this takes a bit of time to get from the bat to your ear!Useful visual picture of the stuff air is made of: GO TO IDEAL GAS SIMULATIONAir is composed of a bunch of nitrogen and oxygen molecules bouncing around and colliding with each other, and with anything else they come across.2What is sound?When you hear the crack of the bat with your ear, what is it that your ear is detecting? a. Electromagnetic radiation that was produced when the bat hit the ball. b. A small change in the pressure of the air that is the result of the bat hitting the ball. c. A wave that travels through the air from the bat to your ear. d. a. and c. e. b. and c.When you hear the crack of the bat with your ear, what is it that your ear is detecting? Answer: e… both b and c.It’s like clapping your hands. When you clap, you push the air causing a slight increase in the pressure of the air followed by a slight decrease in pressure air.This pressure fluctuation travels out in all directions as a wave. As the pressure wave reaches your ear, you hear sound. Just after clapLaterAIR MOLECULESMore densely packed air molecule… Slight increase in pressureSlight decreaseCreating Musical TonesTo create a pure sustained tone (like concert A), the speaker pushes on the air at regular intervals and this pushes on the air creating a series of pressure waves. Higher PLower PIn a speaker the cone vibrates: All musical instruments work on this same principle. They push on the air at regular intervals.Look at sound: Microphone detects changes in pressure. Higher PLower PSound waves traveling outSound waves hit microphone,It flexes, creates electrical signaltimepressureIf the speaker vibrates back and forth 200 times each second, how much time passes between each time it produces a maximum in pressure? a. 0.2 seconds b. 200 seconds c. 0.005 secondsd. 0.02 seconds e. 0.05 secondsHigher PLower PSound waves traveling outAnswer is c. 0.005 seconds. Period = 1 second/ 200 cycles = 0.005 seconds/cycleWhat if we wanted to change the pitch of the tone produced by the speaker? To get a higher pitch sound, we need to adjust the speaker so that: a. It vibrates back and forth more rapidly, taking a smaller amount of time for each cycleb. It vibrates back and forth at the same rate as before, but the range of it’s back and forth motion is larger. c. It receives more powerd. It vibrates back and forth more slowly, taking a longer amount of time for each cyclee. It vibrates back and forth at the same rate as before, but the range of it’s back and forth motion is smaller. Correct answer is a .… It vibrates back and forth more rapidly, taking a smaller amount of time for each cycle … this is adjusting the frequency3The pitch of the sound is determined by the frequency of the vibration:Frequency:The number of times per second that the speaker goes through one complete pushing motionor The number of times per second that the pressure in my ear goes through rise-fall cycle. The frequency of Concert A is 440 Hz, or 440 cycles/secondFGAB | CDEFGAB | CDEFGAB |Octave below Concert A middle C Concert A Octave above Concert A(220 Hz) (256 Hz) (440 Hz) (880 Hz)Range of Human Hearing: 20 Hz to 20,000 Hz How does the wave travel? a. The air molecules I push when I clap travel through air between me and you, and then change the pressure at your ear drum.b. The air molecules I push when I clap will in turn push on the air molecules near them and these will push on the air molecules near them, etc, etc. And this is how the pressure fluctuation travels between me and you. c. I still think sound is electromagnetic radiation.Just after clapLaterAIR MOLECULESWhat happens in the wave? Answer is b. The air molecules I push when I clap will in turn push on the air molecules near them and these will push on the air molecules near them, etc, etc. And this is how the pressure fluctuation travels between me and you. Just after clapLaterAIR MOLECULESI push molecules and they push on molecules near them. The molecules remain pretty much where they started!Like a slinky…. A sound wave is a longitudinal wave … like a slinky: Basically, this means that the motion of the air molecules is towards and away from the source of the sound. This is in contrast to a typical wave, like the wave that forms when I throw a stone in water. In this wave the water is moving up and down, not towards and away from the source of the wave. Motion of air molecule – after sound wave passes, molecule returns to original positionMovement of air: 10-5m for loudest tolerable sound10-11m for faintest of sound we can hearHigher PLower PWavelengthAmplitudeQuestion: If the speaker oscillates at 200 Hz (remember that is completing one cycle in 0.005 seconds), what is the distance between the pressure maximums Recall: the speed of sound = 330 m/sa. 0.6 m b. 1.65 m c. 66,000 m d. 3.3 mb. 1.65 m…. Sound will