Page 133 - Science Class 08

The speed varies with the medium employed Name of the Speed in Metres
(for example, sound waves move faster Medium Per Second
through water than through air), as well as
Air 343
with the proper es of the medium, especially
temperature. Air (saturated) 400
Water 1500
The term is commonly used to refer specifically
Copper 4500
to the speed of sound in air.
Glass 5000
At sea level, at a temperature of 21 degrees
Steel 5000+
Celsius (70 degrees Fahrenheit) and under
Wood 4000+
normal atmospheric condi ons, the speed of
Mercury 1450
sound is 344 m/s (1238 km/h or 770 miles/h).
Cork 550
The speed varies depending on atmospheric
Rubber 30-70
condi ons; the most important factor is the
temperature. We can find the speed of sound using this

Humidity has li le effect on the speed of formula:
sound. Air pressure has almost no effect on Distance travelled by sound
Speed of sound =
speed of sound. It has no effect at all in an ideal Time taken
gas approxima on.
Lightening and thunder : We have read about
This is because pressure and density both the speed of light in the previous chapter. It is
contribute to sound velocity equally and in an about 300,000 kilometers per second. And we
ideal gas the two effects cancel out, leaving can compare the speed of sound with it from
only the effect of temperature. the above table. Clearly, sound travels at a

Sound usually travels more slowly with greater speed much slower than that of light.
al tude, due to reduced temperature. This fact explains why we see a flash of ligh ng
We can know the speed of sound if we divide earlier than we hear the thunder of the clouds
the distance covered by it in a certain me by when they are produced together.
that me. As sound travels at different speeds

in different mediums, its speed differs in
different mediums.
Observe the following table to know about
speeds of sound through different mediums.

Vibration : To-and-fro motion of a clock-pendulam
Tuning fork : An instrument in experiments regarding sound

Sensation : Knowledge obtained by the use of one sense organ or more than one
Audible : A sound that can be clearly heard

Oscillation : One complete (back-and-forth) round of vibration of a body

Science-8 133