The speed of sound depends on its medium.
Suppose you are in the baseball stands during an exciting game. A
pitch flies from the mound toward home plate, and you see the batter
draw back, swing, and hit the ball high. A split second later you hear
the crack of the bat meeting the ball. You notice that the sound of
the hit comes later than the sight. Just how fast does sound travel?
Sound travels more slowly than light, and it does not always travel
at the same speed. Two main factors affect the speed of sound: the
material that makes up the medium—such as air or water—and the
temperature. If we know the medium and the temperature, however,
we can predict the speed of sound.
Which two factors affect the speed of sound?
The Effect of the Material
You have probably heard sounds in more than one medium.
Think about the medium in which you most often hear sound—air.
You listen to a radio or a compact disk player. You hear the siren of a
fire truck. These sound waves travel through air, a mixture of gases.
Now think about going swimming. You dip below the water’s
surface briefly. Someone jumps into the water nearby and splashes water
against the pool wall. You hear strange underwater
sounds. These sound waves travel through water,
a liquid.
Sound travels faster through liquids than it
does through gases because liquids are denser than
gases. That means that the particles are packed
closer together. It takes less time for a water
particle to push on the water particles around it
because the particles are already closer together
than are the particles in air. As a result, divers
underwater would hear a sound sooner than
people above water would.
These divers can hear the
motor of a distant boat
before their friends above
water hear it.
Materials and Sound Speeds
Medium
State
Speed of Sound
Air (20°C)
Gas
344 m/s (769 mi/h)
Water (20°C)
Liquid
1,400 m/s (3,130 mi/h)
Steel (20°C)
Solid
5,000 m/s (11,200 mi/h)
474 Unit 4: Waves, Sound, and Light
Sound can also travel through solid materials
that are elastic, which means they can vibrate back
and forth. In solid materials, the particles are
packed even closer together than they are in liquids
or gases. Steel is an example of an elastic material
that is very dense. Sound travels very rapidly
through steel. Look at the chart on the left.
Compare the speed of sound in air with the speed
of sound in steel.