The most common types of lever are Class 1
and Class2 because they give you a Mechanical Advantage. This means you can move a large
load using a small effort. The mechanical advantage of the Class 1 lever shown below is
found by comparing the weight of the load with the effort needed to move it.
Did you see! Yes I saw that.
Class 3 levers are used less often because
their mechanical advantage is less than 1. This means the force needed to use them is
greater than the force they can move.
Load 50N 5
MA = ---- = ---- = - = 5:1 or 5
Effort 10N 1
VELOCITY RATIO
With class one and class 2 levers it seems
that you are getting something for nothing but of course this is not true. You have to
move the effort a great distance to enable you to move the load a short distance and this
can be seen in the diagram above. A comparison of these distances gives the velocity
ratio.
Distance moved by EFFORT
500mm 5
VR = ------------------------ = ------ = -- = 5:1 or 5
Distance moved by LOAD
100mm 1
All this assumes that the efficiency of
the mechanism is 100% but of course it never is. Bending of parts, friction and twisting
cause mechanisms to be less efficient. Efficiency can be calculated by the formula:
MA
Efficiency = ---- X 100%
VR
4
So then if a mechanism has an MA of 4 and a VR of 5 the Efficiency = --- X 100% = 80%
5
