The radio is pretty amazing, even today. We turn it on, and out comes sound, sound sent from miles and miles away. The radio is over a hundred years old and we were sitting around it listening to music and news long before the television was even dreamed up. After a hundred years of progress the radio hasn't changed much--it's still providing us with music nearly anywhere we go, just about 24/7, and it's still using good old radio waves.
Definition of Radio
Radio is "wireless telegraphy or telephony: speeches broadcast by radio." However "radio" describes the tool with which we receive this wireless transmission. Radio means anything associated with radio waves.
History of Radio
In 1906 some folks aboard a ship who where used to hearing the blips and bleeps of Morse code all day and transcribing it down were treated to a special surprise. They heard over their transmissions the sound of a violin--it was Christmas Eve so the violin was playing "Silent Night." It was magical then, but the idea of creating a public medium out of the ingenious invention came a whole decade later with Frank Conrad who began playing records for his friends over the air, thus radio as we know it was born.
How It Works
Radio waves can bounce around all they want, but no one is going to hear or "intercept" them without a receiver. A radio wave is transmitted from a station's giant transmitter, and these waves go out into the air, in all directions. Your radio antenna, whether external or built into your AM/FM radio, picks up pieces of this wave. The waves don't actually transmit sounds--they carry electronic pulses, and your radio translates these pulses into sound, but all before you can blink your eyes a few times.
FM Radio Vs. AM
Radio
AM (amplitude modulation) and FM (frequency modulation) radio are the same kind of radio wave. They originate as the exact same radio wave, and are encrypted or "modulated" differently. FM radio has a strong advantage over AM radio because it is less likely to have static from fluctuations in signal due to changes in amplitude. FM radio ignores these fluctuations, producing less static, which provides for a better listening experience.
The Physics
When you listen to your radio you are hearing the movement of atoms. When a radio signal is sent it is made up of lots of atoms that have dispersed from the transmitter antenna to the air. These atoms then travel at light speed in all directions until they reach a radio antenna. Radio transmission may seem like sound just bouncing around in the air, but it's actually a transfer of physical matter.
http://www.ehow.com/about_6655125_definition-am-fm-radio.html
