Introduction

Abstract

A mechanical system, or machine, generally consists of a power source and a mechanism for the controlled use of this power. The power may originate as the flow of water or the expansion of steam that drives a turbine and rotates an input shaft to the mechanism. It may be that instead the turbine rotates a generator and the resulting electricity is used to actuate a distant electric motor connected to the mechanism input. Another power source is the expansion of pressurized fluid or burning air–fuel mixture against a piston in order to drive its linear movement inside a cylinder. The purpose of the mechanism is to transform this input power into a useful application of forces combined with a desired movement. For this reason, machines are often defined abstractly as devices that transform energy from one form, such as heat or chemical energy, into another form, usually work.