Main parts of a machine
Cars, aircraft, tractors, ships and machine tools are all machines; they make human work easier. Every machine is built of separate parts – units and components: the more complex the machine, the more parts it has. Parts found in many machines are called standard parts; those used only in some machines are special parts. A bolt is a rod with a head and a thread on one end; a nut is a part with a threaded hole that is screwed onto the bolt. A screw is a threaded rod whose threaded part goes into a thread inside a part. A shaft transmits turning force, a pulley is the wheel-like part of a belt drive, and a bearing lets shafts and axles turn freely. A gear moves another part with its teeth.
Paper “dismantling”: the pupil draws a bicycle and marks bolts, nuts, the gear (sprocket) and bearings. Taking a real machine or a bicycle apart at home is done only by adults.