It is thought that steam engines were invented at about 350 years ago but, the Greek mathematician and engineer Hero of Alexandria worked with air pressure and steam to create rotary motion. Heron (c. 10 – 70 AD) built the „Aeolipile‟ that consists of a sphere on top of a water kettle. A fire below thekettle turns the water into steam forcing the gas to pass through pipes to the sphere. Two L-shaped tubes on opposite sides of the sphere allow the gas to escape, causing a rotation movement. This engine was not used very much in ancient Greece due to economic reasons (slaves did the hard work, and they were cheaper than burning wood) and because there were no practical uses for this device during the Old Greek Times.
Describe with your own words, what is an engine?