Maths, Physics Revision

HOME

Sound waves are longitudinal waves produced by mechanical vibrations.   

The amplitude of the wave determines the volume (loudness) of the sound

High pitch

Loud speaker

The loudspeaker vibrates the
air particles and the sound
energy is transferred

BUT REMEMBER IF YOU ARE TRYING MEASURE THE DISTANCE
BETWEEN YOU AND THE OBJECT CAUSING THE ECHO (eg THE
WALL IN THE ABOVE ANIMATION) YOU HAVE TO DIVIDE THE
ANSWER BY 2 BECAUSE THE SOUND TRAVELS TO THE WALL
AND BACK.
Therefore if the echo above was heard after 4 seconds the sound would
have travelled 4 x 330  = 1320 metres
The distance to the wall would therefore be 1320÷ 2 = 660 metres

This tequique is more often used with ULTRASOUND

Sound waves can be reflected, echoes are evidence of this.
        It is possible to calculate distance using echoes If you
rearrange the speed equation
Speed = distance
           time
You get    distance = speed x time
The speed of sound in air is 330 m/s, so if you measure
the time before you hear the echo and multiply
this by 330 you get the distance the sound
has travelled.

ECHOES

Uses of Ultrasound

Depth sounding

The pulse and echo are shown on the screen of an
oscilloscope. The time between the pulse and the echo
Is shown on the X axis. Sometimes  smaller echo pulses are
seen between the two larger pulses. This could occur when a
shoal of fish pass beneath the boat. Fishing boats use
ultrasound in this way as fish finders

Pre-natal scans

Ultrasonic waves are partially
reflected at the boundaries of
materials of differing densities
the amount of wave reflected
depends on the extent of the
difference in density

An image of an unborn baby can be built up using theses
reflections

Utrasound is also used in medicine to treat gall stones and
kidney stones

Ultrasound is used in industry to scan materials for internal
defects and for cleaning
Some tooth brushes use utrasonic waves \to clean between
teeth