Drawing first-class levers This line diagram shows how to represent a first-class lever.


Figure 5 Line drawing of a first-class lever Activity 1 Draw a first-class lever


1 Draw a neat freehand sketch of a pair of pliers. 2 Label the fulcrum and where the effort is applied. 3 Use pencil crayons to add colour and shading to your drawing.


Activity 2 Compare the mechanical advantage in scissors and secateurs


1 Using the information given on the drawing of the scissors, calculate the mechanical advantage.


2 Now think about when you cut paper. In most cases you will open the scissors wide and place the paper near the pivot position to start the cut. You are then likely to move the paper down when you get about halfway down the blade. The force resistance of the paper is 0,5 N. Calculate the mechanical advantage when the paper is halfway down the length of the blade.


Second-class levers


In first-class levers, the load and the effort is placed on either side of the fulcrum although their distance from the fulcrum does not have to be the same.


In second-class levers, the fulcrum is at one end of the lever and the effort is applied at the other end. The load to be lifted lies between the effort and the fulcrum. With this kind of lever, the effort is always further


102 Topic 5 Mechanical systems and control


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