Mechanical Devices

Pick up a pair of nail clippers. Your thumb pushes down with a force you could apply all day, and at the other end two blades cut through a material that would blunt a kitchen knife. Nothing in the clippers generates any force at all. Every newton at the blades came from your thumb, and the clippers simply rearranged it, trading a long movement for a short one and a small force for a large one.

That trade is what mechanical devices do, and it is the whole of this lesson. You will learn the functions of mechanical devices that produce linear, rotary, reciprocating and oscillating movements, and how they change the magnitude and direction of force. You will meet levers of the first, second and third classes, linkages including bell cranks and push and pull arrangements, and rotary systems: cams and followers, simple gear trains, and pulleys and belts. You will calculate mechanical advantage, gear ratios and output speeds, and you will choose between three ways of doing the same job on a real product. This is core technical principles content, examined in Section A of Paper 1, where it supplied question 8 of the specimen paper.