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Dr. Martin Cooper of Motorola, made the first US analogue mobile phone call on a larger prototype model in 1973. This is a reenactment in 2007
Signal sampling representation. The continuous signal is represented with a green color whereas the discrete samples are in blue.
A full size model of the Earth observation satellite ERS 2
A satellite is an object that orbits another object. With sufficient tangential velocity, the object does not collide with the primary object it orbits, but maintains a distance from that object as the rate at which it falls towards that object is similar to the rate that it travels away, thus the object orbits the primary object and becomes a satellite. In other words: gravitational force serves as the centripetal force needed to make the object circle the primary object. The motion of the satellite around its primary gravitational source is known as freefall.
Radio is a technology that allows for the transmission of signals by modulation of electromagnetic waves. These waves travel (propagate) through the air and the vacuum of space equally well, not requiring a medium of transport.
The telephone or phone is a telecommunications device designed to transmit speech by means of electric signals. It was invented around 1860 by Antonio Meucci who called it teletrophone. The first recorded public demonstration of Meucci's invention took place in 1860, and had a description of it published in New York's Italian language newspaper. In 1861 Philipp Reis presented a machine for electronic voice transmission. Elisha Gray independently invented it and demonstrated it in 1874, but two hours before he submitted his patent announcement, Alexander Graham Bell submitted a patent (although his proposed design did not work). As a result, Alexander Graham Bell is usually credited with the invention.
