The speed of sound
Is about 330m/s in air, which is slower than the Concorde (a supersonic turbo passenger jet) but about four times faster than a racing car.
Variables affect the speed of sound
The speed of sound depends on temperature of the air for example the speed of sound when traveling through dry air at 0º will travel at 330 m/s whereas sound waves traveling through dry air at 30° will travel at 350 m/s.
Sound wave travel faster through liquids or gases, but sound travels fastest in solids for example sound travels through: air at 330 m/s, pure water (0º) at 1400 m/s and concrete at 5000 m/s
Variables that don’t affect sound
The speed of sound doesn’t depend on the pressure of the air if atmospheric pressure changes the speed of sound doesn’t change.
Refraction of sound
Distant noise often sound louder at night this is because the air near the ground cool faster than those above, layers nearer to the ground become colder than the layers above it, and because sound waves travel more slowly in colder air. As a result sound waves leaving the ground tend to bend back toward the ground, instead of spreading upwards. A bending effect like this is caused by a change in speed, this is called refraction
The human ear can only hear sounds from about 20Hz to about 20,000Hz any sound above that range is called ultrasonic sound or ultrasound.
Uses of ultra sound
Cleaning
Using ultrasound, delicate machinery can be cleaned without being dismantled. The machinery is immersed in a tank of liquid; vibrations of high power ultrasound are used to dislodge bits of grease and dirt
Breaking
In hospitals, concentrated beams of ultrasound are used to break up kidney stones and gall stones without patients needing surgery
Echo sounding
Ships use echo sounders to measure the depth of the water beneath them. An echo sounder sends pulses of ultrasound downwards towards the sea floor then measures the time taken for each echo (reflected sound) to come back, the longer the time the deeper the water.
Echo-location
Bats use echo location to locate insects and other objects in front of it. It sends out a series of ultrasound pulses and uses it’s specially shaped ears to pick up the echo.
metal testing
Ultra sound can be used to detect flaws in metals. A pulse of ultrasound is sent through the metal. If there is a flaw (a tiny gap) in the metal, two reflected pulses are picked up by the detector. The pulse that is reflected by the flaw returns first followed by the pulse from the far end of the metal, the pulses can be displayed by a machine called an oscilloscope, the picture on the oscilloscope is a graph showing how the amplitude (strength) of the ultra sound varies with time
scanning the womb
Ultrasound can be used to see inside the womb. A transmitter sends out pulses of ultrasound in to the mothers’ body, the transmitter also acts as a detector and picks up pulses reflected by the baby and different layers of the body. The signals are processed by a computer and turned into an image on a screen.
Ultrasound is a better and safer way of scanning the womb because x-rays can cause cell damage inside a developing baby Also ultrasound can distinguish between different layers of tissue which an ordinary x-ray machine cannot.
