Wheels and axles

Ask your friends what they think is humankind's greatest invention, and make a note of what they choose. They might say for example, the laser ,the spade rocket, the sili-con chip, the computer or the television. But arguably it is none of these. It is something much simpler- the wheel. The invention of the wheel is thought to have taken place about 5,500 years old. Today, wheels in one from or another are found is most vehicles and engines an in other machines and gadgets of all kinds, from wristwatch- es to locomotives.