machine

Today we live in a world that is dominated by machines. in the home,machines vacuum the carpet,wash the dishes and launder the clothes. On the farm, machines plow the land ,sow the seeds, and reap the harvest. In industry, machines spin cloth, hammer metal in to shape, hoist up heavy loads and dig minerals out  the ground. In transportation, vehicles of every kind-- from bikes and cars to trucks and locomotives- transport us and our goods from place to place. Exactly what is a machine ? Scientists tell us that a machine is a device that  performs work. In a more popular sanse ,a machine is a device that help us carry out a particular task more easily and usually much faster. For example, it is difficult for us to till the soil with only our hands . It is much easier if we use a spade,A spade is a simple machine. It is even easier to till the soil if we use powered digging machine, like a rototiller, which has an engine that drives rotating blades. Usually, when we use in the book , we investigate some of the pernici- ples behind the machines we use. We also look at engines- the machines that drive other machines, and some typical machines at work . You can checks answers to the questions features throughout this book on pages 60-61.