Did You Know

	Julius Caesar, a Roman emperor in the 1st century BC, tried to control noise pollution by banning chariots from driving through Rome after dark.
	In 1831, soldiers marching in rhythm across a bridge in England accidentally caused it to collapse. This led to "breaking step" when troops march across bridges.
	In 1876, Alexander Graham Bell, a Scottish inventor, invented the first telephone.
	In 1877, Thomas Edison made the first sound recording and invented the phonograph.
	The loudest sound ever recorded occurred in 1883 when a volcano named Krakatoa erupted off the coast of Sumatra. The island collapsed into the ocean and the explosion was heard 1,900 miles away in the Indian Ocean.
	Bats can hear higher sounds than any other animal, up to 210,000 Hz..
	Crickets have ears on their knees.
	Hummingbirds beat their wings so fast (over 80 times per second) they make a humming sound as they fly.
	Astronauts can communicate in space by putting their helmets together and then speaking. The sound travels through the helmets by vibrations.
	A humpback whale can make sounds louder than the Concorde on takeoff. These sounds can be heard underwater for thousands of miles.
	Supersonic flights that are restricted over land are allowed over the ocean. There is still sonic boom over the ocean. But there are far fewer people to be disturbed than on land.
	In 1976, the Concorde, the world's first supersonic aircraft, was the first commercial aircraft to break the sound barrier.
Mach 1	The speed of sound in aircraft is called Mach 1. Mach 2 is twice the speed of sound.
Sssshhhhhh...	Sound reflects extremely well in the Whispering Gallery of St. Paul's Cathedral, London. When you stand on one side of the dome, you can hear someone whisper against the opposite wall which is 36 meters away.
	The "Doppler Effect" is the strange distortion in sound when an ambulance with a loud siren goes past. We hear the siren as a high-pitched scream and then the sound rapidly drops in pitch as it mves away. In fact, there is no change in pitch; it only appears to change because the waves reach you faster as the vehicle gets closer.