The Effect of Temperature
Sound also travels faster through a medium
at higher temperatures than at lower ones.
Consider the medium of air, a mixture of
gases. Gas particles are not held tightly together
as are particles in solids. Instead, the gas
particles bounce all around. The higher the
temperature, the more the gas particles wiggle
and bounce. It takes less time for particles that
are already moving quickly to push against the
particles around them than it takes particles
that are moving slowly. Sound, therefore,
travels faster in hot air than in cold air.
These snowboarders’
shouts reach their
friends more slowly
in this cold air than
they would in hot air.
Look at the picture of the snowboarders.
The sound waves they make by yelling will
Temperature and Sound Speeds
travel more slowly through air than similar
Medium
Temperature
Speed of Sound
sounds made on a hot day. If you could bear
Air
0ºC (32ºF)
331 m/s (741 mi/h)
to stand in air at a temperature of 100°C
Air
100ºC (212ºF) 386 m/s (864 mi/h)
(212°F—the boiling point of water) and listen
to the same person yelling, you might notice
that the sound of the person’s voice reaches you faster.
The chart on the right shows the speed of sound in air at two
different temperatures. Compare the speed of sound at the temperature
at which water freezes with the speed of sound at the temperature
at which water boils. Sound travels about 17 percent faster in air at
100°C than in air at 0°C.
What is the difference between the speed of sound in air at 0ºC
and at 100ºC?
KEY CONCEPTS
CRITICAL THINKING
1. Describe how sound waves
are produced.
4. Predict Would the sound
from a distant train travel
faster through air or through
steel train tracks? Explain.
2. Describe how particles move as
energy is transferred through a
sound wave.
3. Explain how temperature
affects the speed of sound.
5. Evaluate Suppose an
audience watching a science
fiction movie hears a loud roar
as a spaceship explodes in
outer space. Why is this scene
unrealistic?
CHALLENGE
6. Evaluate A famous riddle
asks this question: If a tree falls
in the forest and there is no
one there to hear it, is there
any sound? What do you
think? Give reasons for your
answer.
Chapter 14: Sound 475