This document discusses the basics of sound waves. It explains that sound waves are caused by vibrations, requiring a medium like air, liquid or solid to transfer energy. It describes how compression and rarefaction of molecules transfers sound waves. Frequency determines pitch, with higher frequencies being higher pitched. Amplitude determines loudness, with greater amplitude being louder. Graphs can show the displacement over time of sound waves to represent characteristics like frequency and amplitude. The speed of sound depends on the medium and temperature.

1. Sound
Physics Power Points
Physics I
Mr. Young
www.pedagogics.ca

2. Basic facts about sound waves:
Sound waves are caused by vibrations.
The source of all sound waves is a vibrating object.
For example: a speaker cone, a guitar string, a
drum skin, an air column in a trumpet.
Sound waves are longitudinal.
Sound waves are mechanical waves. They
require a medium to transfer energy. Sound can
travel through solids, liquids and gases.

3. Sound waves are caused by vibrations
When a tuning fork is struck, the tines vibrate back
and forth. Each vibration compresses the
surrounding air molecules together (high
pressure). Air is elastic. As the compression
expands, adjacent molecules are compressed. In
this way sound waves travel through the medium.
rarefaction
l
compression
Sound waves are
longitudinal
Molecules vibrate
parallel to energy
transfer.

4. Sound waves are mechanical waves

5. Sound waves are mechanical waves
Sound relies on the vibration of particles to
transfer the energy of the sound wave. If there
are no particles, there is no sound!
Bell in Jar Demo - Video

6. Frequency of Sound Waves
The frequency of a sound wave is described as the
pitch of a sound. The higher the frequency of the
vibrating source, the higher the pitch.
Humans can hear sounds in the
range of 20 Hz to 20 kHz. Dogs
and other animals can perceive
higher frequencies (why you
can’t hear a dog whistle.

7. Amplitude of Sound Waves
The amplitude of a sound wave is perceived as the
loudness of a sound. The greater the amplitude
of the vibrating source, the more energy the sound
wave has and your hear a louder noise.
Loudness is measured in decibels (dB). It is
a logarithmic scale. 10 times more energy
gives a +10 dB increase in loudness.

8. Graphical Representations of Sound Waves
A microphone can be used with a data logger to
create a graphical representation of a sound wave.
A displacement-time graph for a sound wave shows
the frequency and amplitude of vibration of the
wave.
Time is measured on the x-axis and the y-axis is
representative of displacement.

9. Graphical Representations of Sound Waves
Example 1 – Showing high pitch (frequency)
http://onlinetonegenerator.com/

10. Graphical Representations of Sound Waves
Example 2 – Showing low pitch (frequency)

11. Graphical Representations of Sound Waves
Showing
loudness

12. Graphical Representations of Sound Waves
Musical instruments do not produce pure tones.
The wave form is still distinguishable in this
recorder sound wave pattern.

13. Speed of Sound
The speed of sound depends on the medium that it
is traveling through. In general:
Vsolid > vliquid > vgas
Specific properties of the medium will also affect
the speed. For example, the speed of sound is
slower in cold air than in warm air. Why is this?

14. Speed of Sound
The speed of sound in still air can be determined by
the following equation:
v = 331 + 0.6T m/s
Where T is the temperature in Celsius.
When we discuss speed in Mach numbers (example
Mach 1.4) we are referring to how fast one is
traveling relative to the speed of sound. Mach 1.4
is slower on a cold day than on a warm one.