Download - Lesson 3 Properties of Sound Waves - PBworks
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PROPERTIES OF SOUND WAVESLearning Goals:
I will be able to describe the different types of “sound” based on their wavelengths.
I will be able to calculate the speed of sound at various temperatures.
I will be able to determine Mach Numbers.
I will be able to calculate sound intensity.
I will learn about safe levels of sound.
DAY 1
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CATEGORIES OF SOUND WAVES• Audible sound waves – sound waves that humans can hear (20 Hz to 20kHz)
• Infrasonic waves – sound waves with a frequency below 20 hz
• Ultrasonic waves – sound waves with a frequency above 20 kHz
THE SPEED OF SOUND
• The speed of sound depends on the density of the air and its temperature.
• The speed of sound in air is 331.4 m/s and increases by 0.606 m/s for every increase in temp by 1°C
• Formula:
v = 331.4 m/s + (0.606 m/s/°C)T
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EXAMPLE 1
Determine the speed of sound in air if the temperature outside is 30°C.
EXAMPLE 2
If the speed of sound in air is measured to be 316 m/s, what is the outside temperature?
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MACH NUMBER
• Mach is used to describe air speeds in terms of the speed of sound.
• There are no units so we would say Mach 1, Mach 0.75, etc.
• Formula:
M �airspeedofobject
localspeedofsound
SUPERSONIC SPEED
• Supersonic speed is a rate of travel of an object that exceeds the speed of sound (Mach 1). For objects traveling in dry air of a temperature of 20 °C (68 °F) at sea level, this speed is approximately 343 m/s, 1,125 ft/s, 768 mph, 667 knots, or 1,235 km/h.
• https://www.youtube.com/watch?v=gWGLAAYdbbc
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EXAMPLE 3
An aircraft is flying at 905 km/h in air at the temperature of -35 °C. Calculate the Mach Number associated with this speed.
TODAY’S TASKS
•Pg. 393 #1-3
•Pg 394 #1-3
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SOUND INTENSITY
• Loudness describes how humans perceive sound energy. It is dependent on a quality called sound intensity.
• Sound intensity is the amount of sound energy being transferred per unit area.
• It is measured in decibels (dB).
SOUND SAFETY
• Any sound levels over 100 dB for more than a few minutes can harm your hearing.
• http://www.noiseaddicts.com/2011/06/mosquito-ringtones/