UNIT 1


Revise levers and gears


In this unit you will:


• calculate the mechanical advantage of a first-class lever • draw a first-class lever • compare the mechanical advantage in scissors and secateurs • sketch and draw levers.


Machines come in all shapes and sizes. Some are used in factories, some in our homes and, if you look around your school, you will find examples there too. All machines have one thing in common – they all do work. Machines make our work easier, because they give us a mechanical advantage (MA). Perhaps one of the simplest and earliest examples of a machine is the lever.


Levers


A lever is a bar that rests on a point called a fulcrum. The bar can tilt or pivot around the fulcrum. When effort is applied at one end of the lever, by pulling or pushing down on it, the lever will move up or down around the fulcrum. This movement can then be used to lift a weight or load at the other end.


Levers are divided into three groups: first-, second- and third-class levers. These names do not mean that one type of lever is better than another. The word class in this case is an abbreviation for the word classification. It is a means of categorising them according to the position of the load, effort and fulcrum.


First-class levers


In the simplest example of a first-class lever, the load and the effort are applied at an equal distance from the fulcrum. The mechanism is in balance. A good example of a first-class lever is a beam scale used for accurately weighing items (see Figure 1).


Figure 1 A beam scale 100 Topic 5 Mechanical systems and control


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38