5/1/2016

1

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

5/1/2016

2

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

5/1/2016

3

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?

5/1/2016

4

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

5/1/2016

5

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

5/1/2016

6

DAY 2

THE SPEED OF SOUND IN VARIOUS MEDIA

• Pg. 395

5/1/2016

7

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/

5/1/2016

8

TODAY’S TASKS

• Pg. 397 #2-10 (you’ll need to use your personal device for research purposes.