Sound waves are mechanical longitudinal waves that cause changes in air pressure as they propagate. The speed of sound waves depends on the medium and properties like temperature, with colder air slowing sound waves more. When sound waves move between media with different speeds, they refract or change direction toward the medium where they travel faster. For example, sound bending downward toward a lake surface due to cooler air near the water amplifying the sound intensity over distance.

1. Sound Waves and Their
Refraction in Air

2. ● Particular type of mechanical wave.
● Longitudinal waves (molecules are
displaced parallel to the direction of
propagation of the wave, and create
regions of higher and lower pressure).
Sound Waves: The Basics

4. ● The speed of a sound wave depends heavily
on the characteristics of the medium in it is
which is travelling through.
● It is not determined by the frequency nor
amplitude of the sound wave.
Speed of Sound

5. ● Refraction refers to a wave that bends when entering a medium
because of a change in its speed.
● This phenomenon also occurs with light, in cameras, for example.
● To visualize this better, let’s think of a toy car. When it rolls on a
smooth floor, its velocity tends to be fast, but as soon as it
reaches a carpeted floor, its velocity changes and its direction
changes as well.
● Similarly, as the particles of a sound wave move from one
medium to another, its speed, as well as their direction, changes.
Refraction of Sound: What is it?

7. ● The direction of propagation of the wave is
deflected.
● The wavelength of the wave decreases
because, since velocity changes but
frequency does not, wavelength changes as
well, according to v=fƛ.
What does refraction imply?

8. ● Sound waves are not refracted as
abruptly as light, but the sound wave
speed changes gradually over a given
distance, because of the difference in
temperature of the medium, in this case,
air.
How does refraction in air work?

9. ● Temperature decreases with height, and
thus speed of sound also decreases with
height. Temperature and speed of sound
are directly proportional.
● If the air above the earth is warmer than at
the surface, sound will be bent back
downward toward the surface by refraction!
How does refraction in air work?

11. What are some examples?
Natural Amplifiers

12. ● On a large lake, it is possible to hear sounds clearly
over a long distance.
● This is due to the difference in temperature in the air
near the surface of the water, which is much cooler
than the air well above the water.
● Sound waves are refracted down to the surface of the
lake, making the intensity of the sound not radiated
uniformly in all directions (isotropically).
Natural Amplifiers

14. ● Hawkes, Robert. Physics for Scientists and Engineers: An
Interactive Approach. Ch. 15, section 15.6. Toronto: Nelson
Education, 2014. 437-440. Print.
● “Refraction of Sound.” Refraction of Sound. N.p.,n.d. Web 20
Feb. 2015. http://hyperphysics.phy-
astr.gsu.edu/hbase/sound/refrac.html#c1
● Russell, Daniel. A. Refraction of Sound Waves. Pennsylvania State
University. 2011. Web. 20 Feb. 2015.
http://www.acs.psu.edu/drussell/Demos/refract/refract.html
Works Cited